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--===========================================================================-- -- -- -- Synthesizable 6809 instruction compatible VHDL CPU core -- -- -- --===========================================================================-- -- -- File name : cpu09.vhd -- -- Entity name : cpu09 -- -- Purpose : 6809 instruction compatible CPU core written in VHDL -- Not cycle compatible with the original 6809 CPU -- -- Dependencies : ieee.std_logic_1164 -- ieee.std_logic_unsigned -- -- Author : John E. Kent -- -- Email : dilbert57@opencores.org -- -- Web : http://opencores.org/project,system09 -- -- -- Copyright (C) 2003 - 2010 John Kent -- -- This program is free software: you can redistribute it and/or modify -- it under the terms of the GNU General Public License as published by -- the Free Software Foundation, either version 3 of the License, or -- (at your option) any later version. -- -- This program is distributed in the hope that it will be useful, -- but WITHOUT ANY WARRANTY; without even the implied warranty of -- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the -- GNU General Public License for more details. -- -- You should have received a copy of the GNU General Public License -- along with this program. If not, see <http://www.gnu.org/licenses/>. -- --===========================================================================-- -- -- -- Revision History -- -- -- --===========================================================================-- -- -- Version 0.1 - 26 June 2003 - John Kent -- Added extra level in state stack -- fixed some calls to the extended addressing state -- -- Version 0.2 - 5 Sept 2003 - John Kent -- Fixed 16 bit indexed offset (was doing read rather than fetch) -- Added/Fixed STY and STS instructions. -- ORCC_STATE ANDed CC state rather than ORed it - Now fixed -- CMPX Loaded ACCA and ACCB - Now fixed -- -- Version 1.0 - 6 Sep 2003 - John Kent -- Initial release to Open Cores -- reversed clock edge -- -- Version 1.1 - 29 November 2003 John kent -- ACCA and ACCB indexed offsets are 2's complement. -- ALU Right Mux now sign extends ACCA & ACCB offsets -- Absolute Indirect addressing performed a read on the -- second byte of the address rather than a fetch -- so it formed an incorrect address. Now fixed. -- -- Version 1.2 - 29 November 2003 John Kent -- LEAX and LEAY affect the Z bit only -- LEAS and LEAU do not affect any condition codes -- added an extra ALU control for LEA. -- -- Version 1.3 - 12 December 2003 John Kent -- CWAI did not work, was missed a PUSH_ST on calling -- the ANDCC_STATE. Thanks go to Ghassan Kraidy for -- finding this fault. -- -- Version 1.4 - 12 December 2003 John Kent -- Missing cc_ctrl assignment in otherwise case of -- lea_state resulted in cc_ctrl being latched in -- that state. -- The otherwise statement should never be reached, -- and has been fixed simply to resolve synthesis warnings. -- -- Version 1.5 - 17 january 2004 John kent -- The clear instruction used "alu_ld8" to control the ALU -- rather than "alu_clr". This mean the Carry was not being -- cleared correctly. -- -- Version 1.6 - 24 January 2004 John Kent -- Fixed problems in PSHU instruction -- -- Version 1.7 - 25 January 2004 John Kent -- removed redundant "alu_inx" and "alu_dex' -- Removed "test_alu" and "test_cc" -- STD instruction did not set condition codes -- JMP direct was not decoded properly -- CLR direct performed an unwanted read cycle -- Bogus "latch_md" in Page2 indexed addressing -- -- Version 1.8 - 27 January 2004 John Kent -- CWAI in decode1_state should increment the PC. -- ABX is supposed to be an unsigned addition. -- Added extra ALU function -- ASR8 slightly changed in the ALU. -- -- Version 1.9 - 20 August 2005 -- LSR8 is now handled in ASR8 and ROR8 case in the ALU, -- rather than LSR16. There was a problem with single -- operand instructions using the MD register which is -- sign extended on the first 8 bit fetch. -- -- Version 1.10 - 13 September 2005 -- TFR & EXG instructions did not work for the Condition Code Register -- An extra case has been added to the ALU for the alu_tfr control -- to assign the left ALU input (alu_left) to the condition code -- outputs (cc_out). -- -- Version 1.11 - 16 September 2005 -- JSR ,X should not predecrement S before calculating the jump address. -- The reason is that JSR [0,S] needs S to point to the top of the stack -- to fetch a valid vector address. The solution is to have the addressing -- mode microcode called before decrementing S and then decrementing S in -- JSR_STATE. JSR_STATE in turn calls PUSH_RETURN_LO_STATE rather than -- PUSH_RETURN_HI_STATE so that both the High & Low halves of the PC are -- pushed on the stack. This adds one extra bus cycle, but resolves the -- addressing conflict. I've also removed the pre-decement S in -- JSR EXTENDED as it also calls JSR_STATE. -- -- Version 1.12 - 6th June 2006 -- 6809 Programming reference manual says V is not affected by ASR, LSR and ROR -- This is different to the 6800. CLR should reset the V bit. -- -- Version 1.13 - 7th July 2006 -- Disable NMI on reset until S Stack pointer has been loaded. -- Added nmi_enable signal in sp_reg process and nmi_handler process. -- -- Version 1.14 - 11th July 2006 -- 1. Added new state to RTI called rti_entire_state. -- This state tests the CC register after it has been loaded -- from the stack. Previously the current CC was tested which -- was incorrect. The Entire Flag should be set before the -- interrupt stacks the CC. -- 2. On bogus Interrupts, int_cc_state went to rti_state, -- which was an enumerated state, but not defined anywhere. -- rti_state has been changed to rti_cc_state so that bogus interrupt -- will perform an RTI after entering that state. -- 3. Sync should generate an interrupt if the interrupt masks -- are cleared. If the interrupt masks are set, then an interrupt -- will cause the the PC to advance to the next instruction. -- Note that I don't wait for an interrupt to be asserted for -- three clock cycles. -- 4. Added new ALU control state "alu_mul". "alu_mul" is used in -- the Multiply instruction replacing "alu_add16". This is similar -- to "alu_add16" except it sets the Carry bit to B7 of the result -- in ACCB, sets the Zero bit if the 16 bit result is zero, but -- does not affect The Half carry (H), Negative (N) or Overflow (V) -- flags. The logic was re-arranged so that it adds md or zero so -- that the Carry condition code is set on zero multiplicands. -- 5. DAA (Decimal Adjust Accumulator) should set the Negative (N) -- and Zero Flags. It will also affect the Overflow (V) flag although -- the operation is undefined. It's anyones guess what DAA does to V. -- -- Version 1.15 - 25th Feb 2007 - John Kent -- line 9672 changed "if Halt <= '1' then" to "if Halt = '1' then" -- Changed sensitivity lists. -- -- Version 1.16 - 5th February 2008 - John Kent -- FIRQ interrupts should take priority over IRQ Interrupts. -- This presumably means they should be tested for before IRQ -- when they happen concurrently. -- -- Version 1.17 - 18th February 2008 - John Kent -- NMI in CWAI should mask IRQ and FIRQ interrupts -- -- Version 1.18 - 21st February 2008 - John Kent -- Removed default register settings in each case statement -- and placed them at the beginning of the state sequencer. -- Modified the SYNC instruction so that the interrupt vector(iv) -- is not set unless an unmasked FIRQ or IRQ is received. -- -- Version 1.19 - 25th February 2008 - John Kent -- Enumerated separate states for FIRQ/FAST and NMIIRQ/ENTIRE -- Enumerated separate states for MASKI and MASKIF states -- Removed code on BSR/JSR in fetch cycle -- library ieee; use ieee.std_logic_1164.all; use ieee.std_logic_unsigned.all; entity cpu09 is port ( clk : in std_logic; rst : in std_logic; vma : out std_logic; addr : out std_logic_vector(15 downto 0); rw : out std_logic; data_out : out std_logic_vector(7 downto 0); data_in : in std_logic_vector(7 downto 0); irq : in std_logic; firq : in std_logic; nmi : in std_logic; halt : in std_logic; hold : in std_logic ); end cpu09; architecture rtl of cpu09 is constant EBIT : integer := 7; constant FBIT : integer := 6; constant HBIT : integer := 5; constant IBIT : integer := 4; constant NBIT : integer := 3; constant ZBIT : integer := 2; constant VBIT : integer := 1; constant CBIT : integer := 0; -- -- Interrupt vector modifiers -- constant RST_VEC : std_logic_vector(2 downto 0) := "111"; constant NMI_VEC : std_logic_vector(2 downto 0) := "110"; constant SWI_VEC : std_logic_vector(2 downto 0) := "101"; constant IRQ_VEC : std_logic_vector(2 downto 0) := "100"; constant FIRQ_VEC : std_logic_vector(2 downto 0) := "011"; constant SWI2_VEC : std_logic_vector(2 downto 0) := "010"; constant SWI3_VEC : std_logic_vector(2 downto 0) := "001"; constant RESV_VEC : std_logic_vector(2 downto 0) := "000"; type state_type is (-- Start off in Reset reset_state, -- Fetch Interrupt Vectors (including reset) vect_lo_state, vect_hi_state, -- Fetch Instruction Cycle fetch_state, -- Decode Instruction Cycles decode1_state, decode2_state, decode3_state, -- Calculate Effective Address imm16_state, indexed_state, index8_state, index16_state, index16_2_state, pcrel8_state, pcrel16_state, pcrel16_2_state, indexaddr_state, indexaddr2_state, postincr1_state, postincr2_state, indirect_state, indirect2_state, indirect3_state, extended_state, -- single ops single_op_read_state, single_op_exec_state, single_op_write_state, -- Dual op states dual_op_read8_state, dual_op_read16_state, dual_op_read16_2_state, dual_op_write8_state, dual_op_write16_state, -- sync_state, halt_state, error_state, -- andcc_state, orcc_state, tfr_state, exg_state, exg1_state, lea_state, -- Multiplication mul_state, mulea_state, muld_state, mul0_state, mul1_state, mul2_state, mul3_state, mul4_state, mul5_state, mul6_state, mul7_state, -- Branches lbranch_state, sbranch_state, -- Jumps, Subroutine Calls and Returns jsr_state, jmp_state, push_return_hi_state, push_return_lo_state, pull_return_hi_state, pull_return_lo_state, -- Interrupt cycles int_nmiirq_state, int_firq_state, int_entire_state, int_fast_state, int_pcl_state, int_pch_state, int_upl_state, int_uph_state, int_iyl_state, int_iyh_state, int_ixl_state, int_ixh_state, int_dp_state, int_accb_state, int_acca_state, int_cc_state, int_cwai_state, int_maski_state, int_maskif_state, -- Return From Interrupt rti_cc_state, rti_entire_state, rti_acca_state, rti_accb_state, rti_dp_state, rti_ixl_state, rti_ixh_state, rti_iyl_state, rti_iyh_state, rti_upl_state, rti_uph_state, rti_pcl_state, rti_pch_state, -- Push Registers using SP pshs_state, pshs_pcl_state, pshs_pch_state, pshs_upl_state, pshs_uph_state, pshs_iyl_state, pshs_iyh_state, pshs_ixl_state, pshs_ixh_state, pshs_dp_state, pshs_acca_state, pshs_accb_state, pshs_cc_state, -- Pull Registers using SP puls_state, puls_cc_state, puls_acca_state, puls_accb_state, puls_dp_state, puls_ixl_state, puls_ixh_state, puls_iyl_state, puls_iyh_state, puls_upl_state, puls_uph_state, puls_pcl_state, puls_pch_state, -- Push Registers using UP pshu_state, pshu_pcl_state, pshu_pch_state, pshu_spl_state, pshu_sph_state, pshu_iyl_state, pshu_iyh_state, pshu_ixl_state, pshu_ixh_state, pshu_dp_state, pshu_acca_state, pshu_accb_state, pshu_cc_state, -- Pull Registers using UP pulu_state, pulu_cc_state, pulu_acca_state, pulu_accb_state, pulu_dp_state, pulu_ixl_state, pulu_ixh_state, pulu_iyl_state, pulu_iyh_state, pulu_spl_state, pulu_sph_state, pulu_pcl_state, pulu_pch_state ); type stack_type is array(2 downto 0) of state_type; type st_type is (idle_st, push_st, pull_st ); type addr_type is (idle_ad, fetch_ad, read_ad, write_ad, pushu_ad, pullu_ad, pushs_ad, pulls_ad, int_hi_ad, int_lo_ad ); type dout_type is (cc_dout, acca_dout, accb_dout, dp_dout, ix_lo_dout, ix_hi_dout, iy_lo_dout, iy_hi_dout, up_lo_dout, up_hi_dout, sp_lo_dout, sp_hi_dout, pc_lo_dout, pc_hi_dout, md_lo_dout, md_hi_dout ); type op_type is (reset_op, fetch_op, latch_op ); type pre_type is (reset_pre, fetch_pre, latch_pre ); type cc_type is (reset_cc, load_cc, pull_cc, latch_cc ); type acca_type is (reset_acca, load_acca, load_hi_acca, pull_acca, latch_acca ); type accb_type is (reset_accb, load_accb, pull_accb, latch_accb ); type dp_type is (reset_dp, load_dp, pull_dp, latch_dp ); type ix_type is (reset_ix, load_ix, pull_lo_ix, pull_hi_ix, latch_ix ); type iy_type is (reset_iy, load_iy, pull_lo_iy, pull_hi_iy, latch_iy ); type sp_type is (reset_sp, latch_sp, load_sp, pull_hi_sp, pull_lo_sp ); type up_type is (reset_up, latch_up, load_up, pull_hi_up, pull_lo_up ); type pc_type is (reset_pc, latch_pc, load_pc, pull_lo_pc, pull_hi_pc, incr_pc ); type md_type is (reset_md, latch_md, load_md, fetch_first_md, fetch_next_md, shiftl_md ); type ea_type is (reset_ea, latch_ea, load_ea, fetch_first_ea, fetch_next_ea ); type iv_type is (latch_iv, reset_iv, nmi_iv, irq_iv, firq_iv, swi_iv, swi2_iv, swi3_iv, resv_iv); type nmi_type is (reset_nmi, set_nmi, latch_nmi ); type left_type is (cc_left, acca_left, accb_left, dp_left, ix_left, iy_left, up_left, sp_left, accd_left, md_left, pc_left, ea_left ); type right_type is (ea_right, zero_right, one_right, two_right, acca_right, accb_right, accd_right, md_right, md_sign5_right, md_sign8_right ); type alu_type is (alu_add8, alu_sub8, alu_add16, alu_sub16, alu_adc, alu_sbc, alu_and, alu_ora, alu_eor, alu_tst, alu_inc, alu_dec, alu_clr, alu_neg, alu_com, alu_lsr16, alu_lsl16, alu_ror8, alu_rol8, alu_mul, alu_asr8, alu_asl8, alu_lsr8, alu_andcc, alu_orcc, alu_sex, alu_tfr, alu_abx, alu_seif, alu_sei, alu_see, alu_cle, alu_ld8, alu_st8, alu_ld16, alu_st16, alu_lea, alu_nop, alu_daa ); signal op_code: std_logic_vector(7 downto 0); signal pre_code: std_logic_vector(7 downto 0); signal acca: std_logic_vector(7 downto 0); signal accb: std_logic_vector(7 downto 0); signal cc: std_logic_vector(7 downto 0); signal cc_out: std_logic_vector(7 downto 0); signal dp: std_logic_vector(7 downto 0); signal xreg: std_logic_vector(15 downto 0); signal yreg: std_logic_vector(15 downto 0); signal sp: std_logic_vector(15 downto 0); signal up: std_logic_vector(15 downto 0); signal ea: std_logic_vector(15 downto 0); signal pc: std_logic_vector(15 downto 0); signal md: std_logic_vector(15 downto 0); signal left: std_logic_vector(15 downto 0); signal right: std_logic_vector(15 downto 0); signal out_alu: std_logic_vector(15 downto 0); signal iv: std_logic_vector(2 downto 0); signal nmi_req: std_logic; signal nmi_ack: std_logic; signal nmi_enable: std_logic; signal state: state_type; signal next_state: state_type; signal saved_state: state_type; signal return_state: state_type; signal state_stack: stack_type; signal st_ctrl: st_type; signal pc_ctrl: pc_type; signal ea_ctrl: ea_type; signal op_ctrl: op_type; signal pre_ctrl: pre_type; signal md_ctrl: md_type; signal acca_ctrl: acca_type; signal accb_ctrl: accb_type; signal ix_ctrl: ix_type; signal iy_ctrl: iy_type; signal cc_ctrl: cc_type; signal dp_ctrl: dp_type; signal sp_ctrl: sp_type; signal up_ctrl: up_type; signal iv_ctrl: iv_type; signal left_ctrl: left_type; signal right_ctrl: right_type; signal alu_ctrl: alu_type; signal addr_ctrl: addr_type; signal dout_ctrl: dout_type; signal nmi_ctrl: nmi_type; begin ---------------------------------- -- -- State machine stack -- ---------------------------------- --state_stack_proc: process( clk, hold, state_stack, st_ctrl, -- return_state, fetch_state ) state_stack_proc: process( clk, state_stack ) begin if clk'event and clk = '0' then if hold= '1' then state_stack(0) <= state_stack(0); state_stack(1) <= state_stack(1); state_stack(2) <= state_stack(2); else case st_ctrl is when idle_st => state_stack(0) <= state_stack(0); state_stack(1) <= state_stack(1); state_stack(2) <= state_stack(2); when push_st => state_stack(0) <= return_state; state_stack(1) <= state_stack(0); state_stack(2) <= state_stack(1); when pull_st => state_stack(0) <= state_stack(1); state_stack(1) <= state_stack(2); state_stack(2) <= fetch_state; when others => state_stack(0) <= state_stack(0); state_stack(1) <= state_stack(1); state_stack(2) <= state_stack(2); end case; end if; end if; saved_state <= state_stack(0); end process; ---------------------------------- -- -- Program Counter Control -- ---------------------------------- --pc_reg: process( clk, pc_ctrl, hold, pc, out_alu, data_in ) pc_reg: process( clk ) begin if clk'event and clk = '0' then if hold= '1' then pc <= pc; else case pc_ctrl is when reset_pc => pc <= "0000000000000000"; when load_pc => pc <= out_alu(15 downto 0); when pull_lo_pc => pc(7 downto 0) <= data_in; when pull_hi_pc => pc(15 downto 8) <= data_in; when incr_pc => pc <= pc + 1; when others => -- when latch_pc => pc <= pc; end case; end if; end if; end process; ---------------------------------- -- -- Effective Address Control -- ---------------------------------- --ea_reg: process( clk, ea_ctrl, hold, ea, out_alu, data_in, dp ) ea_reg: process( clk ) begin if clk'event and clk = '0' then if hold= '1' then ea <= ea; else case ea_ctrl is when reset_ea => ea <= "0000000000000000"; when fetch_first_ea => ea(7 downto 0) <= data_in; ea(15 downto 8) <= dp; when fetch_next_ea => ea(15 downto 8) <= ea(7 downto 0); ea(7 downto 0) <= data_in; when load_ea => ea <= out_alu(15 downto 0); when others => -- when latch_ea => ea <= ea; end case; end if; end if; end process; -------------------------------- -- -- Accumulator A -- -------------------------------- --acca_reg : process( clk, acca_ctrl, hold, out_alu, acca, data_in ) acca_reg : process( clk ) begin if clk'event and clk = '0' then if hold= '1' then acca <= acca; else case acca_ctrl is when reset_acca => acca <= "00000000"; when load_acca => acca <= out_alu(7 downto 0); when load_hi_acca => acca <= out_alu(15 downto 8); when pull_acca => acca <= data_in; when others => -- when latch_acca => acca <= acca; end case; end if; end if; end process; -------------------------------- -- -- Accumulator B -- -------------------------------- --accb_reg : process( clk, accb_ctrl, hold, out_alu, accb, data_in ) accb_reg : process( clk ) begin if clk'event and clk = '0' then if hold= '1' then accb <= accb; else case accb_ctrl is when reset_accb => accb <= "00000000"; when load_accb => accb <= out_alu(7 downto 0); when pull_accb => accb <= data_in; when others => -- when latch_accb => accb <= accb; end case; end if; end if; end process; -------------------------------- -- -- X Index register -- -------------------------------- --ix_reg : process( clk, ix_ctrl, hold, out_alu, xreg, data_in ) ix_reg : process( clk ) begin if clk'event and clk = '0' then if hold= '1' then xreg <= xreg; else case ix_ctrl is when reset_ix => xreg <= "0000000000000000"; when load_ix => xreg <= out_alu(15 downto 0); when pull_hi_ix => xreg(15 downto 8) <= data_in; when pull_lo_ix => xreg(7 downto 0) <= data_in; when others => -- when latch_ix => xreg <= xreg; end case; end if; end if; end process; -------------------------------- -- -- Y Index register -- -------------------------------- --iy_reg : process( clk, iy_ctrl, hold, out_alu, yreg, data_in ) iy_reg : process( clk ) begin if clk'event and clk = '0' then if hold= '1' then yreg <= yreg; else case iy_ctrl is when reset_iy => yreg <= "0000000000000000"; when load_iy => yreg <= out_alu(15 downto 0); when pull_hi_iy => yreg(15 downto 8) <= data_in; when pull_lo_iy => yreg(7 downto 0) <= data_in; when others => -- when latch_iy => yreg <= yreg; end case; end if; end if; end process; -------------------------------- -- -- S stack pointer -- -------------------------------- --sp_reg : process( clk, sp_ctrl, hold, sp, out_alu, data_in, nmi_enable ) sp_reg : process( clk ) begin if clk'event and clk = '0' then if hold= '1' then sp <= sp; nmi_enable <= nmi_enable; else case sp_ctrl is when reset_sp => sp <= "0000000000000000"; nmi_enable <= '0'; when load_sp => sp <= out_alu(15 downto 0); nmi_enable <= '1'; when pull_hi_sp => sp(15 downto 8) <= data_in; nmi_enable <= nmi_enable; when pull_lo_sp => sp(7 downto 0) <= data_in; nmi_enable <= '1'; when others => -- when latch_sp => sp <= sp; nmi_enable <= nmi_enable; end case; end if; end if; end process; -------------------------------- -- -- U stack pointer -- -------------------------------- --up_reg : process( clk, up_ctrl, hold, up, out_alu, data_in ) up_reg : process( clk ) begin if clk'event and clk = '0' then if hold= '1' then up <= up; else case up_ctrl is when reset_up => up <= "0000000000000000"; when load_up => up <= out_alu(15 downto 0); when pull_hi_up => up(15 downto 8) <= data_in; when pull_lo_up => up(7 downto 0) <= data_in; when others => -- when latch_up => up <= up; end case; end if; end if; end process; -------------------------------- -- -- Memory Data -- -------------------------------- --md_reg : process( clk, md_ctrl, hold, out_alu, data_in, md ) md_reg : process( clk ) begin if clk'event and clk = '0' then if hold= '1' then md <= md; else case md_ctrl is when reset_md => md <= "0000000000000000"; when load_md => md <= out_alu(15 downto 0); when fetch_first_md => -- sign extend md for branches md(15 downto 8) <= data_in(7) & data_in(7) & data_in(7) & data_in(7) & data_in(7) & data_in(7) & data_in(7) & data_in(7) ; md(7 downto 0) <= data_in; when fetch_next_md => md(15 downto 8) <= md(7 downto 0); md(7 downto 0) <= data_in; when shiftl_md => md(15 downto 1) <= md(14 downto 0); md(0) <= '0'; when others => -- when latch_md => md <= md; end case; end if; end if; end process; ---------------------------------- -- -- Condition Codes -- ---------------------------------- --cc_reg: process( clk, cc_ctrl, hold, cc_out, cc, data_in ) cc_reg: process( clk ) begin if clk'event and clk = '0' then if hold= '1' then cc <= cc; else case cc_ctrl is when reset_cc => cc <= "11010000"; -- set EBIT, FBIT & IBIT when load_cc => cc <= cc_out; when pull_cc => cc <= data_in; when others => -- when latch_cc => cc <= cc; end case; end if; end if; end process; ---------------------------------- -- -- Direct Page register -- ---------------------------------- --dp_reg: process( clk, dp_ctrl, hold, out_alu, dp, data_in ) dp_reg: process( clk ) begin if clk'event and clk = '0' then if hold= '1' then dp <= dp; else case dp_ctrl is when reset_dp => dp <= "00000000"; when load_dp => dp <= out_alu(7 downto 0); when pull_dp => dp <= data_in; when others => -- when latch_dp => dp <= dp; end case; end if; end if; end process; ---------------------------------- -- -- interrupt vector -- ---------------------------------- --iv_mux: process( clk, iv_ctrl, hold, iv ) iv_mux: process( clk ) begin if clk'event and clk = '0' then if hold= '1' then iv <= iv; else case iv_ctrl is when reset_iv => iv <= RST_VEC; when nmi_iv => iv <= NMI_VEC; when swi_iv => iv <= SWI_VEC; when irq_iv => iv <= IRQ_VEC; when firq_iv => iv <= FIRQ_VEC; when swi2_iv => iv <= SWI2_VEC; when swi3_iv => iv <= SWI3_VEC; when resv_iv => iv <= RESV_VEC; when others => iv <= iv; end case; end if; end if; end process; ---------------------------------- -- -- op code register -- ---------------------------------- --op_reg: process( clk, op_ctrl, hold, op_code, data_in ) op_reg: process( clk ) begin if clk'event and clk = '0' then if hold= '1' then op_code <= op_code; else case op_ctrl is when reset_op => op_code <= "00010010"; when fetch_op => op_code <= data_in; when others => -- when latch_op => op_code <= op_code; end case; end if; end if; end process; ---------------------------------- -- -- pre byte op code register -- ---------------------------------- --pre_reg: process( clk, pre_ctrl, hold, pre_code, data_in ) pre_reg: process( clk ) begin if clk'event and clk = '0' then if hold= '1' then pre_code <= pre_code; else case pre_ctrl is when reset_pre => pre_code <= "00000000"; when fetch_pre => pre_code <= data_in; when others => -- when latch_pre => pre_code <= pre_code; end case; end if; end if; end process; -------------------------------- -- -- state machine -- -------------------------------- --change_state: process( clk, rst, state, hold, next_state ) change_state: process( clk ) begin if clk'event and clk = '0' then if rst = '1' then state <= reset_state; else if hold = '1' then state <= state; else state <= next_state; end if; end if; end if; end process; -- output ------------------------------------ -- -- Nmi register -- ------------------------------------ --nmi_reg: process( clk, nmi_ctrl, hold, nmi_ack ) nmi_reg: process( clk ) begin if clk'event and clk='0' then if hold = '1' then nmi_ack <= nmi_ack; else case nmi_ctrl is when set_nmi => nmi_ack <= '1'; when reset_nmi => nmi_ack <= '0'; when others => -- when latch_nmi => nmi_ack <= nmi_ack; end case; end if; end if; end process; ------------------------------------ -- -- Detect Edge of NMI interrupt -- ------------------------------------ --nmi_handler : process( clk, rst, nmi, nmi_ack, nmi_req, nmi_enable ) nmi_handler : process( rst, clk ) begin if rst='1' then nmi_req <= '0'; elsif clk'event and clk='0' then if (nmi='1') and (nmi_ack='0') and (nmi_enable='1') then nmi_req <= '1'; else if (nmi='0') and (nmi_ack='1') then nmi_req <= '0'; end if; end if; end if; end process; ---------------------------------- -- -- Address output multiplexer -- ---------------------------------- addr_mux: process( addr_ctrl, pc, ea, up, sp, iv ) begin case addr_ctrl is when idle_ad => vma <= '0'; addr <= "1111111111111111"; rw <= '1'; when fetch_ad => vma <= '1'; addr <= pc; rw <= '1'; when read_ad => vma <= '1'; addr <= ea; rw <= '1'; when write_ad => vma <= '1'; addr <= ea; rw <= '0'; when pushs_ad => vma <= '1'; addr <= sp; rw <= '0'; when pulls_ad => vma <= '1'; addr <= sp; rw <= '1'; when pushu_ad => vma <= '1'; addr <= up; rw <= '0'; when pullu_ad => vma <= '1'; addr <= up; rw <= '1'; when int_hi_ad => vma <= '1'; addr <= "111111111111" & iv & "0"; rw <= '1'; when int_lo_ad => vma <= '1'; addr <= "111111111111" & iv & "1"; rw <= '1'; when others => vma <= '0'; addr <= "1111111111111111"; rw <= '1'; end case; end process; -------------------------------- -- -- Data Bus output -- -------------------------------- dout_mux : process( dout_ctrl, md, acca, accb, dp, xreg, yreg, sp, up, pc, cc ) begin case dout_ctrl is when cc_dout => -- condition code register data_out <= cc; when acca_dout => -- accumulator a data_out <= acca; when accb_dout => -- accumulator b data_out <= accb; when dp_dout => -- direct page register data_out <= dp; when ix_lo_dout => -- X index reg data_out <= xreg(7 downto 0); when ix_hi_dout => -- X index reg data_out <= xreg(15 downto 8); when iy_lo_dout => -- Y index reg data_out <= yreg(7 downto 0); when iy_hi_dout => -- Y index reg data_out <= yreg(15 downto 8); when up_lo_dout => -- U stack pointer data_out <= up(7 downto 0); when up_hi_dout => -- U stack pointer data_out <= up(15 downto 8); when sp_lo_dout => -- S stack pointer data_out <= sp(7 downto 0); when sp_hi_dout => -- S stack pointer data_out <= sp(15 downto 8); when md_lo_dout => -- alu output data_out <= md(7 downto 0); when md_hi_dout => -- alu output data_out <= md(15 downto 8); when pc_lo_dout => -- low order pc data_out <= pc(7 downto 0); when pc_hi_dout => -- high order pc data_out <= pc(15 downto 8); when others => data_out <= "00000000"; end case; end process; ---------------------------------- -- -- Left Mux -- ---------------------------------- left_mux: process( left_ctrl, acca, accb, cc, dp, xreg, yreg, up, sp, pc, ea, md ) begin case left_ctrl is when cc_left => left(15 downto 8) <= "00000000"; left(7 downto 0) <= cc; when acca_left => left(15 downto 8) <= "00000000"; left(7 downto 0) <= acca; when accb_left => left(15 downto 8) <= "00000000"; left(7 downto 0) <= accb; when dp_left => left(15 downto 8) <= "00000000"; left(7 downto 0) <= dp; when accd_left => left(15 downto 8) <= acca; left(7 downto 0) <= accb; when md_left => left <= md; when ix_left => left <= xreg; when iy_left => left <= yreg; when sp_left => left <= sp; when up_left => left <= up; when pc_left => left <= pc; when others => -- when ea_left => left <= ea; end case; end process; ---------------------------------- -- -- Right Mux -- ---------------------------------- right_mux: process( right_ctrl, md, acca, accb, ea ) begin case right_ctrl is when ea_right => right <= ea; when zero_right => right <= "0000000000000000"; when one_right => right <= "0000000000000001"; when two_right => right <= "0000000000000010"; when acca_right => if acca(7) = '0' then right <= "00000000" & acca(7 downto 0); else right <= "11111111" & acca(7 downto 0); end if; when accb_right => if accb(7) = '0' then right <= "00000000" & accb(7 downto 0); else right <= "11111111" & accb(7 downto 0); end if; when accd_right => right <= acca & accb; when md_sign5_right => if md(4) = '0' then right <= "00000000000" & md(4 downto 0); else right <= "11111111111" & md(4 downto 0); end if; when md_sign8_right => if md(7) = '0' then right <= "00000000" & md(7 downto 0); else right <= "11111111" & md(7 downto 0); end if; when others => -- when md_right => right <= md; end case; end process; ---------------------------------- -- -- Arithmetic Logic Unit -- ---------------------------------- alu: process( alu_ctrl, cc, left, right, out_alu, cc_out ) variable valid_lo, valid_hi : boolean; variable carry_in : std_logic; variable daa_reg : std_logic_vector(7 downto 0); begin case alu_ctrl is when alu_adc | alu_sbc | alu_rol8 | alu_ror8 => carry_in := cc(CBIT); when alu_asr8 => carry_in := left(7); when others => carry_in := '0'; end case; valid_lo := left(3 downto 0) <= 9; valid_hi := left(7 downto 4) <= 9; if (cc(CBIT) = '0') then if( cc(HBIT) = '1' ) then if valid_hi then daa_reg := "00000110"; else daa_reg := "01100110"; end if; else if valid_lo then if valid_hi then daa_reg := "00000000"; else daa_reg := "01100000"; end if; else if( left(7 downto 4) <= 8 ) then daa_reg := "00000110"; else daa_reg := "01100110"; end if; end if; end if; else if ( cc(HBIT) = '1' )then daa_reg := "01100110"; else if valid_lo then daa_reg := "01100000"; else daa_reg := "01100110"; end if; end if; end if; case alu_ctrl is when alu_add8 | alu_inc | alu_add16 | alu_adc | alu_mul => out_alu <= left + right + ("000000000000000" & carry_in); when alu_sub8 | alu_dec | alu_sub16 | alu_sbc => out_alu <= left - right - ("000000000000000" & carry_in); when alu_abx => out_alu <= left + ("00000000" & right(7 downto 0)) ; when alu_and => out_alu <= left and right; -- and/bit when alu_ora => out_alu <= left or right; -- or when alu_eor => out_alu <= left xor right; -- eor/xor when alu_lsl16 | alu_asl8 | alu_rol8 => out_alu <= left(14 downto 0) & carry_in; -- rol8/asl8/lsl16 when alu_lsr16 => out_alu <= carry_in & left(15 downto 1); -- lsr16 when alu_lsr8 | alu_asr8 | alu_ror8 => out_alu <= "00000000" & carry_in & left(7 downto 1); -- ror8/asr8/lsr8 when alu_neg => out_alu <= right - left; -- neg (right=0) when alu_com => out_alu <= not left; when alu_clr | alu_ld8 | alu_ld16 | alu_lea => out_alu <= right; -- clr, ld when alu_st8 | alu_st16 | alu_andcc | alu_orcc | alu_tfr => out_alu <= left; when alu_daa => out_alu <= left + ("00000000" & daa_reg); when alu_sex => if left(7) = '0' then out_alu <= "00000000" & left(7 downto 0); else out_alu <= "11111111" & left(7 downto 0); end if; when others => out_alu <= left; -- nop end case; -- -- carry bit -- case alu_ctrl is when alu_add8 | alu_adc => cc_out(CBIT) <= (left(7) and right(7)) or (left(7) and not out_alu(7)) or (right(7) and not out_alu(7)); when alu_sub8 | alu_sbc => cc_out(CBIT) <= ((not left(7)) and right(7)) or ((not left(7)) and out_alu(7)) or (right(7) and out_alu(7)); when alu_add16 => cc_out(CBIT) <= (left(15) and right(15)) or (left(15) and not out_alu(15)) or (right(15) and not out_alu(15)); when alu_sub16 => cc_out(CBIT) <= ((not left(15)) and right(15)) or ((not left(15)) and out_alu(15)) or (right(15) and out_alu(15)); when alu_ror8 | alu_lsr16 | alu_lsr8 | alu_asr8 => cc_out(CBIT) <= left(0); when alu_rol8 | alu_asl8 => cc_out(CBIT) <= left(7); when alu_lsl16 => cc_out(CBIT) <= left(15); when alu_com => cc_out(CBIT) <= '1'; when alu_neg | alu_clr => cc_out(CBIT) <= out_alu(7) or out_alu(6) or out_alu(5) or out_alu(4) or out_alu(3) or out_alu(2) or out_alu(1) or out_alu(0); when alu_mul => cc_out(CBIT) <= out_alu(7); when alu_daa => if ( daa_reg(7 downto 4) = "0110" ) then cc_out(CBIT) <= '1'; else cc_out(CBIT) <= '0'; end if; when alu_andcc => cc_out(CBIT) <= left(CBIT) and cc(CBIT); when alu_orcc => cc_out(CBIT) <= left(CBIT) or cc(CBIT); when alu_tfr => cc_out(CBIT) <= left(CBIT); when others => cc_out(CBIT) <= cc(CBIT); end case; -- -- Zero flag -- case alu_ctrl is when alu_add8 | alu_sub8 | alu_adc | alu_sbc | alu_and | alu_ora | alu_eor | alu_inc | alu_dec | alu_neg | alu_com | alu_clr | alu_rol8 | alu_ror8 | alu_asr8 | alu_asl8 | alu_lsr8 | alu_ld8 | alu_st8 | alu_sex | alu_daa => cc_out(ZBIT) <= not( out_alu(7) or out_alu(6) or out_alu(5) or out_alu(4) or out_alu(3) or out_alu(2) or out_alu(1) or out_alu(0) ); when alu_add16 | alu_sub16 | alu_mul | alu_lsl16 | alu_lsr16 | alu_ld16 | alu_st16 | alu_lea => cc_out(ZBIT) <= not( out_alu(15) or out_alu(14) or out_alu(13) or out_alu(12) or out_alu(11) or out_alu(10) or out_alu(9) or out_alu(8) or out_alu(7) or out_alu(6) or out_alu(5) or out_alu(4) or out_alu(3) or out_alu(2) or out_alu(1) or out_alu(0) ); when alu_andcc => cc_out(ZBIT) <= left(ZBIT) and cc(ZBIT); when alu_orcc => cc_out(ZBIT) <= left(ZBIT) or cc(ZBIT); when alu_tfr => cc_out(ZBIT) <= left(ZBIT); when others => cc_out(ZBIT) <= cc(ZBIT); end case; -- -- negative flag -- case alu_ctrl is when alu_add8 | alu_sub8 | alu_adc | alu_sbc | alu_and | alu_ora | alu_eor | alu_rol8 | alu_ror8 | alu_asr8 | alu_asl8 | alu_lsr8 | alu_inc | alu_dec | alu_neg | alu_com | alu_clr | alu_ld8 | alu_st8 | alu_sex | alu_daa => cc_out(NBIT) <= out_alu(7); when alu_add16 | alu_sub16 | alu_lsl16 | alu_lsr16 | alu_ld16 | alu_st16 => cc_out(NBIT) <= out_alu(15); when alu_andcc => cc_out(NBIT) <= left(NBIT) and cc(NBIT); when alu_orcc => cc_out(NBIT) <= left(NBIT) or cc(NBIT); when alu_tfr => cc_out(NBIT) <= left(NBIT); when others => cc_out(NBIT) <= cc(NBIT); end case; -- -- Interrupt mask flag -- case alu_ctrl is when alu_andcc => cc_out(IBIT) <= left(IBIT) and cc(IBIT); when alu_orcc => cc_out(IBIT) <= left(IBIT) or cc(IBIT); when alu_tfr => cc_out(IBIT) <= left(IBIT); when alu_seif | alu_sei => cc_out(IBIT) <= '1'; when others => cc_out(IBIT) <= cc(IBIT); -- interrupt mask end case; -- -- Half Carry flag -- case alu_ctrl is when alu_add8 | alu_adc => cc_out(HBIT) <= (left(3) and right(3)) or (right(3) and not out_alu(3)) or (left(3) and not out_alu(3)); when alu_andcc => cc_out(HBIT) <= left(HBIT) and cc(HBIT); when alu_orcc => cc_out(HBIT) <= left(HBIT) or cc(HBIT); when alu_tfr => cc_out(HBIT) <= left(HBIT); when others => cc_out(HBIT) <= cc(HBIT); end case; -- -- Overflow flag -- case alu_ctrl is when alu_add8 | alu_adc => cc_out(VBIT) <= (left(7) and right(7) and (not out_alu(7))) or ((not left(7)) and (not right(7)) and out_alu(7)); when alu_sub8 | alu_sbc => cc_out(VBIT) <= (left(7) and (not right(7)) and (not out_alu(7))) or ((not left(7)) and right(7) and out_alu(7)); when alu_add16 => cc_out(VBIT) <= (left(15) and right(15) and (not out_alu(15))) or ((not left(15)) and (not right(15)) and out_alu(15)); when alu_sub16 => cc_out(VBIT) <= (left(15) and (not right(15)) and (not out_alu(15))) or ((not left(15)) and right(15) and out_alu(15)); when alu_inc => cc_out(VBIT) <= ((not left(7)) and left(6) and left(5) and left(4) and left(3) and left(2) and left(1) and left(0)); when alu_dec | alu_neg => cc_out(VBIT) <= (left(7) and (not left(6)) and (not left(5)) and (not left(4)) and (not left(3)) and (not left(2)) and (not left(1)) and (not left(0))); -- 6809 Programming reference manual says -- V not affected by ASR, LSR and ROR -- This is different to the 6800 -- John Kent 6th June 2006 -- when alu_asr8 => -- cc_out(VBIT) <= left(0) xor left(7); -- when alu_lsr8 | alu_lsr16 => -- cc_out(VBIT) <= left(0); -- when alu_ror8 => -- cc_out(VBIT) <= left(0) xor cc(CBIT); when alu_lsl16 => cc_out(VBIT) <= left(15) xor left(14); when alu_rol8 | alu_asl8 => cc_out(VBIT) <= left(7) xor left(6); -- -- 11th July 2006 - John Kent -- What DAA does with V is anyones guess -- It is undefined in the 6809 programming manual -- when alu_daa => cc_out(VBIT) <= left(7) xor out_alu(7) xor cc(CBIT); -- CLR resets V Bit -- John Kent 6th June 2006 when alu_and | alu_ora | alu_eor | alu_com | alu_clr | alu_st8 | alu_st16 | alu_ld8 | alu_ld16 | alu_sex => cc_out(VBIT) <= '0'; when alu_andcc => cc_out(VBIT) <= left(VBIT) and cc(VBIT); when alu_orcc => cc_out(VBIT) <= left(VBIT) or cc(VBIT); when alu_tfr => cc_out(VBIT) <= left(VBIT); when others => cc_out(VBIT) <= cc(VBIT); end case; case alu_ctrl is when alu_andcc => cc_out(FBIT) <= left(FBIT) and cc(FBIT); when alu_orcc => cc_out(FBIT) <= left(FBIT) or cc(FBIT); when alu_tfr => cc_out(FBIT) <= left(FBIT); when alu_seif => cc_out(FBIT) <= '1'; when others => cc_out(FBIT) <= cc(FBIT); end case; case alu_ctrl is when alu_andcc => cc_out(EBIT) <= left(EBIT) and cc(EBIT); when alu_orcc => cc_out(EBIT) <= left(EBIT) or cc(EBIT); when alu_tfr => cc_out(EBIT) <= left(EBIT); when alu_see => cc_out(EBIT) <= '1'; when alu_cle => cc_out(EBIT) <= '0'; when others => cc_out(EBIT) <= cc(EBIT); end case; end process; ------------------------------------ -- -- state sequencer -- ------------------------------------ process( state, saved_state, op_code, pre_code, cc, ea, md, iv, irq, firq, nmi_req, nmi_ack, halt ) variable cond_true : boolean; -- variable used to evaluate coditional branches begin -- Registers preserved cc_ctrl <= latch_cc; acca_ctrl <= latch_acca; accb_ctrl <= latch_accb; dp_ctrl <= latch_dp; ix_ctrl <= latch_ix; iy_ctrl <= latch_iy; up_ctrl <= latch_up; sp_ctrl <= latch_sp; pc_ctrl <= latch_pc; md_ctrl <= latch_md; ea_ctrl <= latch_ea; iv_ctrl <= latch_iv; op_ctrl <= latch_op; pre_ctrl <= latch_pre; nmi_ctrl <= latch_nmi; -- ALU Idle left_ctrl <= pc_left; right_ctrl <= zero_right; alu_ctrl <= alu_nop; -- Bus idle addr_ctrl <= idle_ad; dout_ctrl <= cc_dout; -- Next State Fetch st_ctrl <= idle_st; return_state <= fetch_state; next_state <= fetch_state; case state is when reset_state => -- released from reset -- reset the registers op_ctrl <= reset_op; pre_ctrl <= reset_pre; cc_ctrl <= reset_cc; acca_ctrl <= reset_acca; accb_ctrl <= reset_accb; dp_ctrl <= reset_dp; ix_ctrl <= reset_ix; iy_ctrl <= reset_iy; up_ctrl <= reset_up; sp_ctrl <= reset_sp; pc_ctrl <= reset_pc; ea_ctrl <= reset_ea; md_ctrl <= reset_md; iv_ctrl <= reset_iv; nmi_ctrl <= reset_nmi; next_state <= vect_hi_state; -- -- Jump via interrupt vector -- iv holds interrupt type -- fetch PC hi from vector location -- when vect_hi_state => -- fetch pc low interrupt vector pc_ctrl <= pull_hi_pc; addr_ctrl <= int_hi_ad; next_state <= vect_lo_state; -- -- jump via interrupt vector -- iv holds vector type -- fetch PC lo from vector location -- when vect_lo_state => -- fetch the vector low byte pc_ctrl <= pull_lo_pc; addr_ctrl <= int_lo_ad; next_state <= fetch_state; -- -- Here to fetch an instruction -- PC points to opcode -- Should service interrupt requests at this point -- either from the timer -- or from the external input. -- when fetch_state => -- fetch the op code op_ctrl <= fetch_op; pre_ctrl <= fetch_pre; ea_ctrl <= reset_ea; -- Fetch op code addr_ctrl <= fetch_ad; -- case op_code(7 downto 6) is when "10" => -- acca case op_code(3 downto 0) is when "0000" => -- suba left_ctrl <= acca_left; right_ctrl <= md_right; alu_ctrl <= alu_sub8; cc_ctrl <= load_cc; acca_ctrl <= load_acca; when "0001" => -- cmpa left_ctrl <= acca_left; right_ctrl <= md_right; alu_ctrl <= alu_sub8; cc_ctrl <= load_cc; when "0010" => -- sbca left_ctrl <= acca_left; right_ctrl <= md_right; alu_ctrl <= alu_sbc; cc_ctrl <= load_cc; acca_ctrl <= load_acca; when "0011" => case pre_code is when "00010000" => -- page 2 -- cmpd left_ctrl <= accd_left; right_ctrl <= md_right; alu_ctrl <= alu_sub16; cc_ctrl <= load_cc; when "00010001" => -- page 3 -- cmpu left_ctrl <= up_left; right_ctrl <= md_right; alu_ctrl <= alu_sub16; cc_ctrl <= load_cc; when others => -- page 1 -- subd left_ctrl <= accd_left; right_ctrl <= md_right; alu_ctrl <= alu_sub16; cc_ctrl <= load_cc; acca_ctrl <= load_hi_acca; accb_ctrl <= load_accb; end case; when "0100" => -- anda left_ctrl <= acca_left; right_ctrl <= md_right; alu_ctrl <= alu_and; cc_ctrl <= load_cc; acca_ctrl <= load_acca; when "0101" => -- bita left_ctrl <= acca_left; right_ctrl <= md_right; alu_ctrl <= alu_and; cc_ctrl <= load_cc; when "0110" => -- ldaa left_ctrl <= acca_left; right_ctrl <= md_right; alu_ctrl <= alu_ld8; cc_ctrl <= load_cc; acca_ctrl <= load_acca; when "0111" => -- staa left_ctrl <= acca_left; right_ctrl <= md_right; alu_ctrl <= alu_st8; cc_ctrl <= load_cc; when "1000" => -- eora left_ctrl <= acca_left; right_ctrl <= md_right; alu_ctrl <= alu_eor; cc_ctrl <= load_cc; acca_ctrl <= load_acca; when "1001" => -- adca left_ctrl <= acca_left; right_ctrl <= md_right; alu_ctrl <= alu_adc; cc_ctrl <= load_cc; acca_ctrl <= load_acca; when "1010" => -- oraa left_ctrl <= acca_left; right_ctrl <= md_right; alu_ctrl <= alu_ora; cc_ctrl <= load_cc; acca_ctrl <= load_acca; when "1011" => -- adda left_ctrl <= acca_left; right_ctrl <= md_right; alu_ctrl <= alu_add8; cc_ctrl <= load_cc; acca_ctrl <= load_acca; when "1100" => case pre_code is when "00010000" => -- page 2 -- cmpy left_ctrl <= iy_left; right_ctrl <= md_right; alu_ctrl <= alu_sub16; cc_ctrl <= load_cc; when "00010001" => -- page 3 -- cmps left_ctrl <= sp_left; right_ctrl <= md_right; alu_ctrl <= alu_sub16; cc_ctrl <= load_cc; when others => -- page 1 -- cmpx left_ctrl <= ix_left; right_ctrl <= md_right; alu_ctrl <= alu_sub16; cc_ctrl <= load_cc; end case; when "1101" => -- bsr / jsr null; when "1110" => -- ldx case pre_code is when "00010000" => -- page 2 -- ldy left_ctrl <= iy_left; right_ctrl <= md_right; alu_ctrl <= alu_ld16; cc_ctrl <= load_cc; iy_ctrl <= load_iy; when others => -- page 1 -- ldx left_ctrl <= ix_left; right_ctrl <= md_right; alu_ctrl <= alu_ld16; cc_ctrl <= load_cc; ix_ctrl <= load_ix; end case; when "1111" => -- stx case pre_code is when "00010000" => -- page 2 -- sty left_ctrl <= iy_left; right_ctrl <= md_right; alu_ctrl <= alu_st16; cc_ctrl <= load_cc; when others => -- page 1 -- stx left_ctrl <= ix_left; right_ctrl <= md_right; alu_ctrl <= alu_st16; cc_ctrl <= load_cc; end case; when others => null; end case; when "11" => -- accb dual op case op_code(3 downto 0) is when "0000" => -- subb left_ctrl <= accb_left; right_ctrl <= md_right; alu_ctrl <= alu_sub8; cc_ctrl <= load_cc; accb_ctrl <= load_accb; when "0001" => -- cmpb left_ctrl <= accb_left; right_ctrl <= md_right; alu_ctrl <= alu_sub8; cc_ctrl <= load_cc; when "0010" => -- sbcb left_ctrl <= accb_left; right_ctrl <= md_right; alu_ctrl <= alu_sbc; cc_ctrl <= load_cc; accb_ctrl <= load_accb; when "0011" => -- addd left_ctrl <= accd_left; right_ctrl <= md_right; alu_ctrl <= alu_add16; cc_ctrl <= load_cc; acca_ctrl <= load_hi_acca; accb_ctrl <= load_accb; when "0100" => -- andb left_ctrl <= accb_left; right_ctrl <= md_right; alu_ctrl <= alu_and; cc_ctrl <= load_cc; accb_ctrl <= load_accb; when "0101" => -- bitb left_ctrl <= accb_left; right_ctrl <= md_right; alu_ctrl <= alu_and; cc_ctrl <= load_cc; when "0110" => -- ldab left_ctrl <= accb_left; right_ctrl <= md_right; alu_ctrl <= alu_ld8; cc_ctrl <= load_cc; accb_ctrl <= load_accb; when "0111" => -- stab left_ctrl <= accb_left; right_ctrl <= md_right; alu_ctrl <= alu_st8; cc_ctrl <= load_cc; when "1000" => -- eorb left_ctrl <= accb_left; right_ctrl <= md_right; alu_ctrl <= alu_eor; cc_ctrl <= load_cc; accb_ctrl <= load_accb; when "1001" => -- adcb left_ctrl <= accb_left; right_ctrl <= md_right; alu_ctrl <= alu_adc; cc_ctrl <= load_cc; accb_ctrl <= load_accb; when "1010" => -- orab left_ctrl <= accb_left; right_ctrl <= md_right; alu_ctrl <= alu_ora; cc_ctrl <= load_cc; accb_ctrl <= load_accb; when "1011" => -- addb left_ctrl <= accb_left; right_ctrl <= md_right; alu_ctrl <= alu_add8; cc_ctrl <= load_cc; accb_ctrl <= load_accb; when "1100" => -- ldd left_ctrl <= accd_left; right_ctrl <= md_right; alu_ctrl <= alu_ld16; cc_ctrl <= load_cc; acca_ctrl <= load_hi_acca; accb_ctrl <= load_accb; when "1101" => -- std left_ctrl <= accd_left; right_ctrl <= md_right; alu_ctrl <= alu_st16; cc_ctrl <= load_cc; when "1110" => -- ldu case pre_code is when "00010000" => -- page 2 -- lds left_ctrl <= sp_left; right_ctrl <= md_right; alu_ctrl <= alu_ld16; cc_ctrl <= load_cc; sp_ctrl <= load_sp; when others => -- page 1 -- ldu left_ctrl <= up_left; right_ctrl <= md_right; alu_ctrl <= alu_ld16; cc_ctrl <= load_cc; up_ctrl <= load_up; end case; when "1111" => case pre_code is when "00010000" => -- page 2 -- sts left_ctrl <= sp_left; right_ctrl <= md_right; alu_ctrl <= alu_st16; cc_ctrl <= load_cc; when others => -- page 1 -- stu left_ctrl <= up_left; right_ctrl <= md_right; alu_ctrl <= alu_st16; cc_ctrl <= load_cc; end case; when others => null; end case; when others => null; end case; if halt = '1' then iv_ctrl <= reset_iv; next_state <= halt_state; -- service non maskable interrupts elsif (nmi_req = '1') and (nmi_ack = '0') then iv_ctrl <= nmi_iv; nmi_ctrl <= set_nmi; next_state <= int_nmiirq_state; -- service maskable interrupts else -- -- nmi request is not cleared until nmi input goes low -- if(nmi_req = '0') and (nmi_ack='1') then nmi_ctrl <= reset_nmi; end if; -- -- FIRQ & IRQ are level sensitive -- if (firq = '1') and (cc(FBIT) = '0') then iv_ctrl <= firq_iv; next_state <= int_firq_state; elsif (irq = '1') and (cc(IBIT) = '0') then iv_ctrl <= irq_iv; next_state <= int_nmiirq_state; else -- Advance the PC to fetch next instruction byte iv_ctrl <= reset_iv; -- default to reset pc_ctrl <= incr_pc; next_state <= decode1_state; end if; end if; -- -- Here to decode instruction -- and fetch next byte of intruction -- whether it be necessary or not -- when decode1_state => -- fetch first byte of address or immediate data ea_ctrl <= fetch_first_ea; md_ctrl <= fetch_first_md; addr_ctrl <= fetch_ad; case op_code(7 downto 4) is -- -- direct single op (2 bytes) -- 6809 => 6 cycles -- cpu09 => 5 cycles -- 1 op=(pc) / pc=pc+1 -- 2 ea_hi=dp / ea_lo=(pc) / pc=pc+1 -- 3 md_lo=(ea) / pc=pc -- 4 alu_left=md / md=alu_out / pc=pc -- 5 (ea)=md_lo / pc=pc -- -- Exception is JMP -- 6809 => 3 cycles -- cpu09 => 3 cycles -- 1 op=(pc) / pc=pc+1 -- 2 ea_hi=dp / ea_lo=(pc) / pc=pc+1 -- 3 pc=ea -- when "0000" => -- advance the PC pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "1110" => -- jmp next_state <= jmp_state; when "1111" => -- clr next_state <= single_op_exec_state; when others => next_state <= single_op_read_state; end case; -- acca / accb inherent instructions when "0001" => case op_code(3 downto 0) is -- -- Page2 pre byte -- pre=(pc) / pc=pc+1 -- op=(pc) / pc=pc+1 -- when "0000" => -- page2 op_ctrl <= fetch_op; -- advance pc pc_ctrl <= incr_pc; next_state <= decode2_state; -- -- Page3 pre byte -- pre=(pc) / pc=pc+1 -- op=(pc) / pc=pc+1 -- when "0001" => -- page3 op_ctrl <= fetch_op; -- advance pc pc_ctrl <= incr_pc; next_state <= decode3_state; -- -- nop - No operation ( 1 byte ) -- 6809 => 2 cycles -- cpu09 => 2 cycles -- 1 op=(pc) / pc=pc+1 -- 2 decode -- when "0010" => -- nop next_state <= fetch_state; -- -- sync - halt execution until an interrupt is received -- interrupt may be NMI, IRQ or FIRQ -- program execution continues if the -- interrupt is asserted for 3 clock cycles -- note that registers are not pushed onto the stack -- CPU09 => Interrupts need only be asserted for one clock cycle -- when "0011" => -- sync next_state <= sync_state; -- -- lbra -- long branch (3 bytes) -- 6809 => 5 cycles -- cpu09 => 4 cycles -- 1 op=(pc) / pc=pc+1 -- 2 md_hi=sign(pc) / md_lo=(pc) / pc=pc+1 -- 3 md_hi=md_lo / md_lo=(pc) / pc=pc+1 -- 4 pc=pc+md -- when "0110" => -- increment the pc pc_ctrl <= incr_pc; next_state <= lbranch_state; -- -- lbsr - long branch to subroutine (3 bytes) -- 6809 => 9 cycles -- cpu09 => 6 cycles -- 1 op=(pc) /pc=pc+1 -- 2 md_hi=sign(pc) / md_lo=(pc) / pc=pc+1 / sp=sp-1 -- 3 md_hi=md_lo / md_lo=(pc) / pc=pc+1 -- 4 (sp)= pc_lo / sp=sp-1 / pc=pc -- 5 (sp)=pc_hi / pc=pc -- 6 pc=pc+md -- when "0111" => -- pre decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; -- increment the pc pc_ctrl <= incr_pc; next_state <= lbranch_state; when "1001" => -- daa left_ctrl <= acca_left; right_ctrl <= accb_right; alu_ctrl <= alu_daa; cc_ctrl <= load_cc; acca_ctrl <= load_acca; next_state <= fetch_state; when "1010" => -- orcc -- increment the pc pc_ctrl <= incr_pc; st_ctrl <= push_st; return_state <= fetch_state; next_state <= orcc_state; when "1100" => -- andcc -- increment the pc pc_ctrl <= incr_pc; st_ctrl <= push_st; return_state <= fetch_state; next_state <= andcc_state; when "1101" => -- sex -- have sex left_ctrl <= accb_left; right_ctrl <= zero_right; alu_ctrl <= alu_sex; cc_ctrl <= load_cc; acca_ctrl <= load_hi_acca; next_state <= fetch_state; when "1110" => -- exg -- increment the pc pc_ctrl <= incr_pc; next_state <= exg_state; when "1111" => -- tfr -- increment the pc pc_ctrl <= incr_pc; -- call transfer as a subroutine st_ctrl <= push_st; return_state <= fetch_state; next_state <= tfr_state; when others => -- increment the pc pc_ctrl <= incr_pc; next_state <= fetch_state; end case; -- -- Short branch conditional -- 6809 => always 3 cycles -- cpu09 => always = 3 cycles -- 1 op=(pc) / pc=pc+1 -- 2 md_hi=sign(pc) / md_lo=(pc) / pc=pc+1 / test cc -- 3 if cc tru pc=pc+md else pc=pc -- when "0010" => -- branch conditional -- increment the pc pc_ctrl <= incr_pc; next_state <= sbranch_state; -- -- Single byte stack operators -- Do not advance PC -- when "0011" => -- -- lea - load effective address (2+ bytes) -- 6809 => 4 cycles + addressing mode -- cpu09 => 4 cycles + addressing mode -- 1 op=(pc) / pc=pc+1 -- 2 md_lo=(pc) / pc=pc+1 -- 3 calculate ea -- 4 ix/iy/sp/up = ea -- case op_code(3 downto 0) is when "0000" | -- leax "0001" | -- leay "0010" | -- leas "0011" => -- leau -- advance PC pc_ctrl <= incr_pc; st_ctrl <= push_st; return_state <= lea_state; next_state <= indexed_state; -- -- pshs - push registers onto sp stack -- 6809 => 5 cycles + registers -- cpu09 => 3 cycles + registers -- 1 op=(pc) / pc=pc+1 -- 2 ea_lo=(pc) / pc=pc+1 -- 3 if ea(7 downto 0) != "00000000" then sp=sp-1 -- 4 if ea(7) = 1 (sp)=pcl, sp=sp-1 -- 5 if ea(7) = 1 (sp)=pch -- if ea(6 downto 0) != "0000000" then sp=sp-1 -- 6 if ea(6) = 1 (sp)=upl, sp=sp-1 -- 7 if ea(6) = 1 (sp)=uph -- if ea(5 downto 0) != "000000" then sp=sp-1 -- 8 if ea(5) = 1 (sp)=iyl, sp=sp-1 -- 9 if ea(5) = 1 (sp)=iyh -- if ea(4 downto 0) != "00000" then sp=sp-1 -- 10 if ea(4) = 1 (sp)=ixl, sp=sp-1 -- 11 if ea(4) = 1 (sp)=ixh -- if ea(3 downto 0) != "0000" then sp=sp-1 -- 12 if ea(3) = 1 (sp)=dp -- if ea(2 downto 0) != "000" then sp=sp-1 -- 13 if ea(2) = 1 (sp)=accb -- if ea(1 downto 0) != "00" then sp=sp-1 -- 14 if ea(1) = 1 (sp)=acca -- if ea(0 downto 0) != "0" then sp=sp-1 -- 15 if ea(0) = 1 (sp)=cc -- when "0100" => -- pshs -- advance PC pc_ctrl <= incr_pc; next_state <= pshs_state; -- -- puls - pull registers of sp stack -- 6809 => 5 cycles + registers -- cpu09 => 3 cycles + registers -- when "0101" => -- puls -- advance PC pc_ctrl <= incr_pc; next_state <= puls_state; -- -- pshu - push registers onto up stack -- 6809 => 5 cycles + registers -- cpu09 => 3 cycles + registers -- when "0110" => -- pshu -- advance PC pc_ctrl <= incr_pc; next_state <= pshu_state; -- -- pulu - pull registers of up stack -- 6809 => 5 cycles + registers -- cpu09 => 3 cycles + registers -- when "0111" => -- pulu -- advance PC pc_ctrl <= incr_pc; next_state <= pulu_state; -- -- rts - return from subroutine -- 6809 => 5 cycles -- cpu09 => 4 cycles -- 1 op=(pc) / pc=pc+1 -- 2 decode op -- 3 pc_hi = (sp) / sp=sp+1 -- 4 pc_lo = (sp) / sp=sp+1 -- when "1001" => st_ctrl <= push_st; return_state <= fetch_state; next_state <= pull_return_hi_state; -- -- add accb to index register -- *** Note: this is an unsigned addition. -- does not affect any condition codes -- 6809 => 3 cycles -- cpu09 => 2 cycles -- 1 op=(pc) / pc=pc+1 -- 2 alu_left=ix / alu_right=accb / ix=alu_out / pc=pc -- when "1010" => -- abx left_ctrl <= ix_left; right_ctrl <= accb_right; alu_ctrl <= alu_abx; ix_ctrl <= load_ix; next_state <= fetch_state; when "1011" => -- rti next_state <= rti_cc_state; when "1100" => -- cwai #$<cc_mask> -- pre decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; iv_ctrl <= reset_iv; -- increment pc pc_ctrl <= incr_pc; st_ctrl <= push_st; return_state <= int_entire_state; -- set entire flag next_state <= andcc_state; when "1101" => -- mul next_state <= mul_state; when "1111" => -- swi -- predecrement SP left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; iv_ctrl <= swi_iv; next_state <= int_entire_state; when others => next_state <= fetch_state; end case; -- -- Accumulator A Single operand -- source = acca, dest = acca -- Do not advance PC -- Typically 2 cycles 1 bytes -- 1 opcode fetch -- 2 post byte fetch / instruction decode -- Note that there is no post byte -- so do not advance PC in decode cycle -- Re-run opcode fetch cycle after decode -- when "0100" => -- acca single op left_ctrl <= acca_left; case op_code(3 downto 0) is when "0000" => -- neg right_ctrl <= zero_right; alu_ctrl <= alu_neg; acca_ctrl <= load_acca; cc_ctrl <= load_cc; when "0011" => -- com right_ctrl <= zero_right; alu_ctrl <= alu_com; acca_ctrl <= load_acca; cc_ctrl <= load_cc; when "0100" => -- lsr right_ctrl <= zero_right; alu_ctrl <= alu_lsr8; acca_ctrl <= load_acca; cc_ctrl <= load_cc; when "0110" => -- ror right_ctrl <= zero_right; alu_ctrl <= alu_ror8; acca_ctrl <= load_acca; cc_ctrl <= load_cc; when "0111" => -- asr right_ctrl <= zero_right; alu_ctrl <= alu_asr8; acca_ctrl <= load_acca; cc_ctrl <= load_cc; when "1000" => -- asl right_ctrl <= zero_right; alu_ctrl <= alu_asl8; acca_ctrl <= load_acca; cc_ctrl <= load_cc; when "1001" => -- rol right_ctrl <= zero_right; alu_ctrl <= alu_rol8; acca_ctrl <= load_acca; cc_ctrl <= load_cc; when "1010" => -- dec right_ctrl <= one_right; alu_ctrl <= alu_dec; acca_ctrl <= load_acca; cc_ctrl <= load_cc; when "1011" => -- undefined right_ctrl <= zero_right; alu_ctrl <= alu_nop; acca_ctrl <= latch_acca; cc_ctrl <= latch_cc; when "1100" => -- inc right_ctrl <= one_right; alu_ctrl <= alu_inc; acca_ctrl <= load_acca; cc_ctrl <= load_cc; when "1101" => -- tst right_ctrl <= zero_right; alu_ctrl <= alu_st8; acca_ctrl <= latch_acca; cc_ctrl <= load_cc; when "1110" => -- jmp (not defined) right_ctrl <= zero_right; alu_ctrl <= alu_nop; acca_ctrl <= latch_acca; cc_ctrl <= latch_cc; when "1111" => -- clr right_ctrl <= zero_right; alu_ctrl <= alu_clr; acca_ctrl <= load_acca; cc_ctrl <= load_cc; when others => right_ctrl <= zero_right; alu_ctrl <= alu_nop; acca_ctrl <= latch_acca; cc_ctrl <= latch_cc; end case; next_state <= fetch_state; -- -- Single Operand accb -- source = accb, dest = accb -- Typically 2 cycles 1 bytes -- 1 opcode fetch -- 2 post byte fetch / instruction decode -- Note that there is no post byte -- so do not advance PC in decode cycle -- Re-run opcode fetch cycle after decode -- when "0101" => left_ctrl <= accb_left; case op_code(3 downto 0) is when "0000" => -- neg right_ctrl <= zero_right; alu_ctrl <= alu_neg; accb_ctrl <= load_accb; cc_ctrl <= load_cc; when "0011" => -- com right_ctrl <= zero_right; alu_ctrl <= alu_com; accb_ctrl <= load_accb; cc_ctrl <= load_cc; when "0100" => -- lsr right_ctrl <= zero_right; alu_ctrl <= alu_lsr8; accb_ctrl <= load_accb; cc_ctrl <= load_cc; when "0110" => -- ror right_ctrl <= zero_right; alu_ctrl <= alu_ror8; accb_ctrl <= load_accb; cc_ctrl <= load_cc; when "0111" => -- asr right_ctrl <= zero_right; alu_ctrl <= alu_asr8; accb_ctrl <= load_accb; cc_ctrl <= load_cc; when "1000" => -- asl right_ctrl <= zero_right; alu_ctrl <= alu_asl8; accb_ctrl <= load_accb; cc_ctrl <= load_cc; when "1001" => -- rol right_ctrl <= zero_right; alu_ctrl <= alu_rol8; accb_ctrl <= load_accb; cc_ctrl <= load_cc; when "1010" => -- dec right_ctrl <= one_right; alu_ctrl <= alu_dec; accb_ctrl <= load_accb; cc_ctrl <= load_cc; when "1011" => -- undefined right_ctrl <= zero_right; alu_ctrl <= alu_nop; accb_ctrl <= latch_accb; cc_ctrl <= latch_cc; when "1100" => -- inc right_ctrl <= one_right; alu_ctrl <= alu_inc; accb_ctrl <= load_accb; cc_ctrl <= load_cc; when "1101" => -- tst right_ctrl <= zero_right; alu_ctrl <= alu_st8; accb_ctrl <= latch_accb; cc_ctrl <= load_cc; when "1110" => -- jmp (undefined) right_ctrl <= zero_right; alu_ctrl <= alu_nop; accb_ctrl <= latch_accb; cc_ctrl <= latch_cc; when "1111" => -- clr right_ctrl <= zero_right; alu_ctrl <= alu_clr; accb_ctrl <= load_accb; cc_ctrl <= load_cc; when others => right_ctrl <= zero_right; alu_ctrl <= alu_nop; accb_ctrl <= latch_accb; cc_ctrl <= latch_cc; end case; next_state <= fetch_state; -- -- Single operand indexed -- Two byte instruction so advance PC -- EA should hold index offset -- when "0110" => -- indexed single op -- increment the pc pc_ctrl <= incr_pc; st_ctrl <= push_st; case op_code(3 downto 0) is when "1110" => -- jmp return_state <= jmp_state; when "1111" => -- clr return_state <= single_op_exec_state; when others => return_state <= single_op_read_state; end case; next_state <= indexed_state; -- -- Single operand extended addressing -- three byte instruction so advance the PC -- Low order EA holds high order address -- when "0111" => -- extended single op -- increment PC pc_ctrl <= incr_pc; st_ctrl <= push_st; case op_code(3 downto 0) is when "1110" => -- jmp return_state <= jmp_state; when "1111" => -- clr return_state <= single_op_exec_state; when others => return_state <= single_op_read_state; end case; next_state <= extended_state; when "1000" => -- acca immediate -- increment the pc pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "0011" | -- subd # "1100" | -- cmpx # "1110" => -- ldx # st_ctrl <= push_st; return_state <= fetch_state; next_state <= imm16_state; -- -- bsr offset - Branch to subroutine (2 bytes) -- 6809 => 7 cycles -- cpu09 => 5 cycles -- 1 op=(pc) / pc=pc+1 -- 2 md_hi=sign(pc) / md_lo=(pc) / sp=sp-1 / pc=pc+1 -- 3 (sp)=pc_lo / sp=sp-1 -- 4 (sp)=pc_hi -- 5 pc=pc+md -- when "1101" => -- bsr -- pre decrement SP left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; -- st_ctrl <= push_st; return_state <= sbranch_state; next_state <= push_return_lo_state; when others => next_state <= fetch_state; end case; when "1001" => -- acca direct -- increment the pc pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "0011" | -- subd "1100" | -- cmpx "1110" => -- ldx next_state <= dual_op_read16_state; when "0111" => -- sta direct next_state <= dual_op_write8_state; when "1111" => -- stx direct -- idle ALU left_ctrl <= ix_left; right_ctrl <= zero_right; alu_ctrl <= alu_nop; cc_ctrl <= latch_cc; sp_ctrl <= latch_sp; next_state <= dual_op_write16_state; -- -- jsr direct - Jump to subroutine in direct page (2 bytes) -- 6809 => 7 cycles -- cpu09 => 5 cycles -- 1 op=(pc) / pc=pc+1 -- 2 ea_hi=0 / ea_lo=(pc) / sp=sp-1 / pc=pc+1 -- 3 (sp)=pc_lo / sp=sp-1 -- 4 (sp)=pc_hi -- 5 pc=ea -- when "1101" => -- jsr direct -- pre decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; -- st_ctrl <= push_st; return_state <= jmp_state; next_state <= push_return_lo_state; when others => next_state <= dual_op_read8_state; end case; when "1010" => -- acca indexed -- increment the pc pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "0011" | -- subd "1100" | -- cmpx "1110" => -- ldx st_ctrl <= push_st; return_state <= dual_op_read16_state; next_state <= indexed_state; when "0111" => -- staa ,x st_ctrl <= push_st; return_state <= dual_op_write8_state; next_state <= indexed_state; when "1111" => -- stx ,x st_ctrl <= push_st; return_state <= dual_op_write16_state; next_state <= indexed_state; when "1101" => -- jsr ,x -- DO NOT pre decrement SP st_ctrl <= push_st; return_state <= jsr_state; next_state <= indexed_state; when others => st_ctrl <= push_st; return_state <= dual_op_read8_state; next_state <= indexed_state; end case; when "1011" => -- acca extended -- increment the pc pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "0011" | -- subd "1100" | -- cmpx "1110" => -- ldx st_ctrl <= push_st; return_state <= dual_op_read16_state; next_state <= extended_state; when "0111" => -- staa > st_ctrl <= push_st; return_state <= dual_op_write8_state; next_state <= extended_state; when "1111" => -- stx > st_ctrl <= push_st; return_state <= dual_op_write16_state; next_state <= extended_state; when "1101" => -- jsr >extended -- DO NOT pre decrement sp st_ctrl <= push_st; return_state <= jsr_state; next_state <= extended_state; when others => st_ctrl <= push_st; return_state <= dual_op_read8_state; next_state <= extended_state; end case; when "1100" => -- accb immediate -- increment the pc pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "0011" | -- addd # "1100" | -- ldd # "1110" => -- ldu # st_ctrl <= push_st; return_state <= fetch_state; next_state <= imm16_state; when others => next_state <= fetch_state; end case; when "1101" => -- accb direct -- increment the pc pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "0011" | -- addd "1100" | -- ldd "1110" => -- ldu next_state <= dual_op_read16_state; when "0111" => -- stab direct next_state <= dual_op_write8_state; when "1101" => -- std direct next_state <= dual_op_write16_state; when "1111" => -- stu direct next_state <= dual_op_write16_state; when others => next_state <= dual_op_read8_state; end case; when "1110" => -- accb indexed -- increment the pc pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "0011" | -- addd "1100" | -- ldd "1110" => -- ldu st_ctrl <= push_st; return_state <= dual_op_read16_state; next_state <= indexed_state; when "0111" => -- stab indexed st_ctrl <= push_st; return_state <= dual_op_write8_state; next_state <= indexed_state; when "1101" => -- std indexed st_ctrl <= push_st; return_state <= dual_op_write16_state; next_state <= indexed_state; when "1111" => -- stu indexed st_ctrl <= push_st; return_state <= dual_op_write16_state; next_state <= indexed_state; when others => st_ctrl <= push_st; return_state <= dual_op_read8_state; next_state <= indexed_state; end case; when "1111" => -- accb extended -- increment the pc pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "0011" | -- addd "1100" | -- ldd "1110" => -- ldu st_ctrl <= push_st; return_state <= dual_op_read16_state; next_state <= extended_state; when "0111" => -- stab extended st_ctrl <= push_st; return_state <= dual_op_write8_state; next_state <= extended_state; when "1101" => -- std extended st_ctrl <= push_st; return_state <= dual_op_write16_state; next_state <= extended_state; when "1111" => -- stu extended st_ctrl <= push_st; return_state <= dual_op_write16_state; next_state <= extended_state; when others => st_ctrl <= push_st; return_state <= dual_op_read8_state; next_state <= extended_state; end case; when others => null; end case; -- -- Here to decode prefix 2 instruction -- and fetch next byte of intruction -- whether it be necessary or not -- when decode2_state => -- fetch first byte of address or immediate data ea_ctrl <= fetch_first_ea; md_ctrl <= fetch_first_md; addr_ctrl <= fetch_ad; case op_code(7 downto 4) is -- -- lbcc -- long branch conditional -- 6809 => branch 6 cycles, no branch 5 cycles -- cpu09 => always 5 cycles -- 1 pre=(pc) / pc=pc+1 -- 2 op=(pc) / pc=pc+1 -- 3 md_hi=sign(pc) / md_lo=(pc) / pc=pc+1 -- 4 md_hi=md_lo / md_lo=(pc) / pc=pc+1 -- 5 if cond pc=pc+md else pc=pc -- when "0010" => -- increment the pc pc_ctrl <= incr_pc; next_state <= lbranch_state; -- -- Single byte stack operators -- Do not advance PC -- when "0011" => case op_code(3 downto 0) is when "1111" => -- swi 2 -- predecrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; iv_ctrl <= swi2_iv; next_state <= int_entire_state; when others => next_state <= fetch_state; end case; when "1000" => -- acca immediate -- increment the pc pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "0011" | -- cmpd # "1100" | -- cmpy # "1110" => -- ldy # st_ctrl <= push_st; return_state <= fetch_state; next_state <= imm16_state; when others => next_state <= fetch_state; end case; when "1001" => -- acca direct -- increment the pc pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "0011" | -- cmpd < "1100" | -- cmpy < "1110" => -- ldy < next_state <= dual_op_read16_state; when "1111" => -- sty < next_state <= dual_op_write16_state; when others => next_state <= fetch_state; end case; when "1010" => -- acca indexed -- increment the pc pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "0011" | -- cmpd ,ind "1100" | -- cmpy ,ind "1110" => -- ldy ,ind st_ctrl <= push_st; return_state <= dual_op_read16_state; next_state <= indexed_state; when "1111" => -- sty ,ind st_ctrl <= push_st; return_state <= dual_op_write16_state; next_state <= indexed_state; when others => next_state <= fetch_state; end case; when "1011" => -- acca extended -- increment the pc pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "0011" | -- cmpd < "1100" | -- cmpy < "1110" => -- ldy < st_ctrl <= push_st; return_state <= dual_op_read16_state; next_state <= extended_state; when "1111" => -- sty > st_ctrl <= push_st; return_state <= dual_op_write16_state; next_state <= extended_state; when others => next_state <= fetch_state; end case; when "1100" => -- accb immediate -- increment the pc pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "0011" | -- undef # "1100" | -- undef # "1110" => -- lds # st_ctrl <= push_st; return_state <= fetch_state; next_state <= imm16_state; when others => next_state <= fetch_state; end case; when "1101" => -- accb direct -- increment the pc pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "0011" | -- undef < "1100" | -- undef < "1110" => -- lds < next_state <= dual_op_read16_state; when "1111" => -- sts < next_state <= dual_op_write16_state; when others => next_state <= fetch_state; end case; when "1110" => -- accb indexed -- increment the pc pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "0011" | -- undef ,ind "1100" | -- undef ,ind "1110" => -- lds ,ind st_ctrl <= push_st; return_state <= dual_op_read16_state; next_state <= indexed_state; when "1111" => -- sts ,ind st_ctrl <= push_st; return_state <= dual_op_write16_state; next_state <= indexed_state; when others => next_state <= fetch_state; end case; when "1111" => -- accb extended -- increment the pc pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "0011" | -- undef > "1100" | -- undef > "1110" => -- lds > st_ctrl <= push_st; return_state <= dual_op_read16_state; next_state <= extended_state; when "1111" => -- sts > st_ctrl <= push_st; return_state <= dual_op_write16_state; next_state <= extended_state; when others => next_state <= fetch_state; end case; when others => next_state <= fetch_state; end case; -- -- Here to decode instruction -- and fetch next byte of intruction -- whether it be necessary or not -- when decode3_state => ea_ctrl <= fetch_first_ea; md_ctrl <= fetch_first_md; addr_ctrl <= fetch_ad; dout_ctrl <= md_lo_dout; case op_code(7 downto 4) is -- -- Single byte stack operators -- Do not advance PC -- when "0011" => case op_code(3 downto 0) is when "1111" => -- swi3 -- predecrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; iv_ctrl <= swi3_iv; next_state <= int_entire_state; when others => next_state <= fetch_state; end case; when "1000" => -- acca immediate -- increment the pc pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "0011" | -- cmpu # "1100" | -- cmps # "1110" => -- undef # st_ctrl <= push_st; return_state <= fetch_state; next_state <= imm16_state; when others => next_state <= fetch_state; end case; when "1001" => -- acca direct -- increment the pc pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "0011" | -- cmpu < "1100" | -- cmps < "1110" => -- undef < st_ctrl <= idle_st; return_state <= fetch_state; next_state <= dual_op_read16_state; when others => next_state <= fetch_state; end case; when "1010" => -- acca indexed -- increment the pc pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "0011" | -- cmpu ,X "1100" | -- cmps ,X "1110" => -- undef ,X st_ctrl <= push_st; return_state <= dual_op_read16_state; next_state <= indexed_state; when others => next_state <= fetch_state; end case; when "1011" => -- acca extended -- increment the pc pc_ctrl <= incr_pc; case op_code(3 downto 0) is when "0011" | -- cmpu > "1100" | -- cmps > "1110" => -- undef > st_ctrl <= push_st; return_state <= dual_op_read16_state; next_state <= extended_state; when others => next_state <= fetch_state; end case; when others => next_state <= fetch_state; end case; -- -- here if ea holds low byte -- Direct -- Extended -- Indexed -- read memory location -- when single_op_read_state => -- read memory into md md_ctrl <= fetch_first_md; addr_ctrl <= read_ad; dout_ctrl <= md_lo_dout; next_state <= single_op_exec_state; when single_op_exec_state => case op_code(3 downto 0) is when "0000" => -- neg left_ctrl <= md_left; right_ctrl <= zero_right; alu_ctrl <= alu_neg; cc_ctrl <= load_cc; md_ctrl <= load_md; next_state <= single_op_write_state; when "0011" => -- com left_ctrl <= md_left; right_ctrl <= zero_right; alu_ctrl <= alu_com; cc_ctrl <= load_cc; md_ctrl <= load_md; next_state <= single_op_write_state; when "0100" => -- lsr left_ctrl <= md_left; right_ctrl <= zero_right; alu_ctrl <= alu_lsr8; cc_ctrl <= load_cc; md_ctrl <= load_md; next_state <= single_op_write_state; when "0110" => -- ror left_ctrl <= md_left; right_ctrl <= zero_right; alu_ctrl <= alu_ror8; cc_ctrl <= load_cc; md_ctrl <= load_md; next_state <= single_op_write_state; when "0111" => -- asr left_ctrl <= md_left; right_ctrl <= zero_right; alu_ctrl <= alu_asr8; cc_ctrl <= load_cc; md_ctrl <= load_md; next_state <= single_op_write_state; when "1000" => -- asl left_ctrl <= md_left; right_ctrl <= zero_right; alu_ctrl <= alu_asl8; cc_ctrl <= load_cc; md_ctrl <= load_md; next_state <= single_op_write_state; when "1001" => -- rol left_ctrl <= md_left; right_ctrl <= zero_right; alu_ctrl <= alu_rol8; cc_ctrl <= load_cc; md_ctrl <= load_md; next_state <= single_op_write_state; when "1010" => -- dec left_ctrl <= md_left; right_ctrl <= one_right; alu_ctrl <= alu_dec; cc_ctrl <= load_cc; md_ctrl <= load_md; next_state <= single_op_write_state; when "1011" => -- undefined next_state <= fetch_state; when "1100" => -- inc left_ctrl <= md_left; right_ctrl <= one_right; alu_ctrl <= alu_inc; cc_ctrl <= load_cc; md_ctrl <= load_md; next_state <= single_op_write_state; when "1101" => -- tst left_ctrl <= md_left; right_ctrl <= zero_right; alu_ctrl <= alu_st8; cc_ctrl <= load_cc; next_state <= fetch_state; when "1110" => -- jmp left_ctrl <= md_left; right_ctrl <= zero_right; alu_ctrl <= alu_ld16; pc_ctrl <= load_pc; next_state <= fetch_state; when "1111" => -- clr left_ctrl <= md_left; right_ctrl <= zero_right; alu_ctrl <= alu_clr; cc_ctrl <= load_cc; md_ctrl <= load_md; next_state <= single_op_write_state; when others => next_state <= fetch_state; end case; -- -- single operand 8 bit write -- Write low 8 bits of ALU output -- EA holds address -- MD holds data -- when single_op_write_state => -- write ALU low byte output addr_ctrl <= write_ad; dout_ctrl <= md_lo_dout; next_state <= fetch_state; -- -- here if ea holds address of low byte -- read memory location -- when dual_op_read8_state => -- read first data byte from ea md_ctrl <= fetch_first_md; addr_ctrl <= read_ad; next_state <= fetch_state; -- -- Here to read a 16 bit value into MD -- pointed to by the EA register -- The first byte is read -- and the EA is incremented -- when dual_op_read16_state => -- increment the effective address left_ctrl <= ea_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; ea_ctrl <= load_ea; -- read the high byte of the 16 bit data md_ctrl <= fetch_first_md; addr_ctrl <= read_ad; next_state <= dual_op_read16_2_state; -- -- here to read the second byte -- pointed to by EA into MD -- when dual_op_read16_2_state => -- read the low byte of the 16 bit data md_ctrl <= fetch_next_md; addr_ctrl <= read_ad; next_state <= fetch_state; -- -- 16 bit Write state -- EA hold address of memory to write to -- Advance the effective address in ALU -- decode op_code to determine which -- register to write -- when dual_op_write16_state => -- increment the effective address left_ctrl <= ea_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; ea_ctrl <= load_ea; -- write the ALU hi byte at ea addr_ctrl <= write_ad; if op_code(6) = '0' then case op_code(3 downto 0) is when "1111" => -- stx / sty case pre_code is when "00010000" => -- page 2 -- sty dout_ctrl <= iy_hi_dout; when others => -- page 1 -- stx dout_ctrl <= ix_hi_dout; end case; when others => dout_ctrl <= md_hi_dout; end case; else case op_code(3 downto 0) is when "1101" => -- std dout_ctrl <= acca_dout; -- acca is high byte of ACCD when "1111" => -- stu / sts case pre_code is when "00010000" => -- page 2 -- sts dout_ctrl <= sp_hi_dout; when others => -- page 1 -- stu dout_ctrl <= up_hi_dout; end case; when others => dout_ctrl <= md_hi_dout; end case; end if; next_state <= dual_op_write8_state; -- -- Dual operand 8 bit write -- Write 8 bit accumulator -- or low byte of 16 bit register -- EA holds address -- decode opcode to determine -- which register to apply to the bus -- Also set the condition codes here -- when dual_op_write8_state => if op_code(6) = '0' then case op_code(3 downto 0) is when "0111" => -- sta dout_ctrl <= acca_dout; when "1111" => -- stx / sty case pre_code is when "00010000" => -- page 2 -- sty dout_ctrl <= iy_lo_dout; when others => -- page 1 -- stx dout_ctrl <= ix_lo_dout; end case; when others => dout_ctrl <= md_lo_dout; end case; else case op_code(3 downto 0) is when "0111" => -- stb dout_ctrl <= accb_dout; when "1101" => -- std dout_ctrl <= accb_dout; -- accb is low byte of accd when "1111" => -- stu / sts case pre_code is when "00010000" => -- page 2 -- sts dout_ctrl <= sp_lo_dout; when others => -- page 1 -- stu dout_ctrl <= up_lo_dout; end case; when others => dout_ctrl <= md_lo_dout; end case; end if; -- write ALU low byte output addr_ctrl <= write_ad; next_state <= fetch_state; -- -- 16 bit immediate addressing mode -- when imm16_state => -- increment pc pc_ctrl <= incr_pc; -- fetch next immediate byte md_ctrl <= fetch_next_md; addr_ctrl <= fetch_ad; st_ctrl <= pull_st; next_state <= saved_state; -- -- md & ea holds 8 bit index offset -- calculate the effective memory address -- using the alu -- when indexed_state => -- -- decode indexing mode -- if md(7) = '0' then case md(6 downto 5) is when "00" => left_ctrl <= ix_left; when "01" => left_ctrl <= iy_left; when "10" => left_ctrl <= up_left; when others => -- when "11" => left_ctrl <= sp_left; end case; right_ctrl <= md_sign5_right; alu_ctrl <= alu_add16; ea_ctrl <= load_ea; st_ctrl <= pull_st; next_state <= saved_state; else case md(3 downto 0) is when "0000" => -- ,R+ case md(6 downto 5) is when "00" => left_ctrl <= ix_left; when "01" => left_ctrl <= iy_left; when "10" => left_ctrl <= up_left; when others => left_ctrl <= sp_left; end case; -- right_ctrl <= zero_right; alu_ctrl <= alu_add16; ea_ctrl <= load_ea; next_state <= postincr1_state; when "0001" => -- ,R++ case md(6 downto 5) is when "00" => left_ctrl <= ix_left; when "01" => left_ctrl <= iy_left; when "10" => left_ctrl <= up_left; when others => -- when "11" => left_ctrl <= sp_left; end case; right_ctrl <= zero_right; alu_ctrl <= alu_add16; ea_ctrl <= load_ea; next_state <= postincr2_state; when "0010" => -- ,-R case md(6 downto 5) is when "00" => left_ctrl <= ix_left; ix_ctrl <= load_ix; when "01" => left_ctrl <= iy_left; iy_ctrl <= load_iy; when "10" => left_ctrl <= up_left; up_ctrl <= load_up; when others => -- when "11" => left_ctrl <= sp_left; sp_ctrl <= load_sp; end case; right_ctrl <= one_right; alu_ctrl <= alu_sub16; ea_ctrl <= load_ea; st_ctrl <= pull_st; next_state <= saved_state; when "0011" => -- ,--R case md(6 downto 5) is when "00" => left_ctrl <= ix_left; ix_ctrl <= load_ix; when "01" => left_ctrl <= iy_left; iy_ctrl <= load_iy; when "10" => left_ctrl <= up_left; up_ctrl <= load_up; when others => -- when "11" => left_ctrl <= sp_left; sp_ctrl <= load_sp; end case; right_ctrl <= two_right; alu_ctrl <= alu_sub16; ea_ctrl <= load_ea; if md(4) = '0' then st_ctrl <= pull_st; next_state <= saved_state; else next_state <= indirect_state; end if; when "0100" => -- ,R (zero offset) case md(6 downto 5) is when "00" => left_ctrl <= ix_left; when "01" => left_ctrl <= iy_left; when "10" => left_ctrl <= up_left; when others => -- when "11" => left_ctrl <= sp_left; end case; right_ctrl <= zero_right; alu_ctrl <= alu_add16; ea_ctrl <= load_ea; if md(4) = '0' then st_ctrl <= pull_st; next_state <= saved_state; else next_state <= indirect_state; end if; when "0101" => -- ACCB,R case md(6 downto 5) is when "00" => left_ctrl <= ix_left; when "01" => left_ctrl <= iy_left; when "10" => left_ctrl <= up_left; when others => -- when "11" => left_ctrl <= sp_left; end case; right_ctrl <= accb_right; alu_ctrl <= alu_add16; ea_ctrl <= load_ea; if md(4) = '0' then st_ctrl <= pull_st; next_state <= saved_state; else next_state <= indirect_state; end if; when "0110" => -- ACCA,R case md(6 downto 5) is when "00" => left_ctrl <= ix_left; when "01" => left_ctrl <= iy_left; when "10" => left_ctrl <= up_left; when others => -- when "11" => left_ctrl <= sp_left; end case; right_ctrl <= acca_right; alu_ctrl <= alu_add16; ea_ctrl <= load_ea; if md(4) = '0' then st_ctrl <= pull_st; next_state <= saved_state; else next_state <= indirect_state; end if; when "0111" => -- undefined case md(6 downto 5) is when "00" => left_ctrl <= ix_left; when "01" => left_ctrl <= iy_left; when "10" => left_ctrl <= up_left; when others => -- when "11" => left_ctrl <= sp_left; end case; right_ctrl <= zero_right; alu_ctrl <= alu_add16; ea_ctrl <= load_ea; if md(4) = '0' then st_ctrl <= pull_st; next_state <= saved_state; else next_state <= indirect_state; end if; when "1000" => -- offset8,R md_ctrl <= fetch_first_md; -- pick up 8 bit offset addr_ctrl <= fetch_ad; pc_ctrl <= incr_pc; next_state <= index8_state; when "1001" => -- offset16,R md_ctrl <= fetch_first_md; -- pick up first byte of 16 bit offset addr_ctrl <= fetch_ad; pc_ctrl <= incr_pc; next_state <= index16_state; when "1010" => -- undefined case md(6 downto 5) is when "00" => left_ctrl <= ix_left; when "01" => left_ctrl <= iy_left; when "10" => left_ctrl <= up_left; when others => -- when "11" => left_ctrl <= sp_left; end case; right_ctrl <= zero_right; alu_ctrl <= alu_add16; ea_ctrl <= load_ea; -- if md(4) = '0' then st_ctrl <= pull_st; next_state <= saved_state; else next_state <= indirect_state; end if; when "1011" => -- ACCD,R case md(6 downto 5) is when "00" => left_ctrl <= ix_left; when "01" => left_ctrl <= iy_left; when "10" => left_ctrl <= up_left; when others => -- when "11" => left_ctrl <= sp_left; end case; right_ctrl <= accd_right; alu_ctrl <= alu_add16; ea_ctrl <= load_ea; if md(4) = '0' then st_ctrl <= pull_st; next_state <= saved_state; else next_state <= indirect_state; end if; when "1100" => -- offset8,PC -- fetch 8 bit offset md_ctrl <= fetch_first_md; addr_ctrl <= fetch_ad; pc_ctrl <= incr_pc; next_state <= pcrel8_state; when "1101" => -- offset16,PC -- fetch offset md_ctrl <= fetch_first_md; addr_ctrl <= fetch_ad; pc_ctrl <= incr_pc; next_state <= pcrel16_state; when "1110" => -- undefined case md(6 downto 5) is when "00" => left_ctrl <= ix_left; when "01" => left_ctrl <= iy_left; when "10" => left_ctrl <= up_left; when others => -- when "11" => left_ctrl <= sp_left; end case; right_ctrl <= zero_right; alu_ctrl <= alu_add16; ea_ctrl <= load_ea; if md(4) = '0' then st_ctrl <= pull_st; next_state <= saved_state; else next_state <= indirect_state; end if; when others => -- when "1111" => -- [,address] -- advance PC to pick up address md_ctrl <= fetch_first_md; addr_ctrl <= fetch_ad; pc_ctrl <= incr_pc; next_state <= indexaddr_state; end case; end if; -- load index register with ea plus one when postincr1_state => left_ctrl <= ea_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; case md(6 downto 5) is when "00" => ix_ctrl <= load_ix; when "01" => iy_ctrl <= load_iy; when "10" => up_ctrl <= load_up; when others => -- when "11" => sp_ctrl <= load_sp; end case; -- return to previous state if md(4) = '0' then st_ctrl <= pull_st; next_state <= saved_state; else next_state <= indirect_state; end if; -- load index register with ea plus two when postincr2_state => -- increment register by two (address) left_ctrl <= ea_left; right_ctrl <= two_right; alu_ctrl <= alu_add16; case md(6 downto 5) is when "00" => ix_ctrl <= load_ix; when "01" => iy_ctrl <= load_iy; when "10" => up_ctrl <= load_up; when others => -- when "11" => sp_ctrl <= load_sp; end case; -- return to previous state if md(4) = '0' then st_ctrl <= pull_st; next_state <= saved_state; else next_state <= indirect_state; end if; -- -- ea = index register + md (8 bit signed offset) -- ea holds post byte -- when index8_state => case ea(6 downto 5) is when "00" => left_ctrl <= ix_left; when "01" => left_ctrl <= iy_left; when "10" => left_ctrl <= up_left; when others => -- when "11" => left_ctrl <= sp_left; end case; -- ea = index reg + md right_ctrl <= md_sign8_right; alu_ctrl <= alu_add16; ea_ctrl <= load_ea; -- return to previous state if ea(4) = '0' then st_ctrl <= pull_st; next_state <= saved_state; else next_state <= indirect_state; end if; -- fetch low byte of 16 bit indexed offset when index16_state => -- advance pc pc_ctrl <= incr_pc; -- fetch low byte md_ctrl <= fetch_next_md; addr_ctrl <= fetch_ad; next_state <= index16_2_state; -- ea = index register + md (16 bit offset) -- ea holds post byte when index16_2_state => case ea(6 downto 5) is when "00" => left_ctrl <= ix_left; when "01" => left_ctrl <= iy_left; when "10" => left_ctrl <= up_left; when others => -- when "11" => left_ctrl <= sp_left; end case; -- ea = index reg + md right_ctrl <= md_right; alu_ctrl <= alu_add16; ea_ctrl <= load_ea; -- return to previous state if ea(4) = '0' then st_ctrl <= pull_st; next_state <= saved_state; else next_state <= indirect_state; end if; -- -- pc relative with 8 bit signed offest -- md holds signed offset -- when pcrel8_state => -- ea = pc + signed md left_ctrl <= pc_left; right_ctrl <= md_sign8_right; alu_ctrl <= alu_add16; ea_ctrl <= load_ea; -- return to previous state if ea(4) = '0' then st_ctrl <= pull_st; next_state <= saved_state; else next_state <= indirect_state; end if; -- pc relative addressing with 16 bit offset -- pick up the low byte of the offset in md -- advance the pc when pcrel16_state => -- advance pc pc_ctrl <= incr_pc; -- fetch low byte md_ctrl <= fetch_next_md; addr_ctrl <= fetch_ad; next_state <= pcrel16_2_state; -- pc relative with16 bit signed offest -- md holds signed offset when pcrel16_2_state => -- ea = pc + md left_ctrl <= pc_left; right_ctrl <= md_right; alu_ctrl <= alu_add16; ea_ctrl <= load_ea; -- return to previous state if ea(4) = '0' then st_ctrl <= pull_st; next_state <= saved_state; else next_state <= indirect_state; end if; -- indexed to address -- pick up the low byte of the address -- advance the pc when indexaddr_state => -- advance pc pc_ctrl <= incr_pc; -- fetch low byte md_ctrl <= fetch_next_md; addr_ctrl <= fetch_ad; next_state <= indexaddr2_state; -- indexed to absolute address -- md holds address -- ea hold indexing mode byte when indexaddr2_state => -- ea = md left_ctrl <= pc_left; right_ctrl <= md_right; alu_ctrl <= alu_ld16; ea_ctrl <= load_ea; -- return to previous state if ea(4) = '0' then st_ctrl <= pull_st; next_state <= saved_state; else next_state <= indirect_state; end if; -- -- load md with high byte of indirect address -- pointed to by ea -- increment ea -- when indirect_state => -- increment ea left_ctrl <= ea_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; ea_ctrl <= load_ea; -- fetch high byte md_ctrl <= fetch_first_md; addr_ctrl <= read_ad; next_state <= indirect2_state; -- -- load md with low byte of indirect address -- pointed to by ea -- ea has previously been incremented -- when indirect2_state => -- fetch high byte md_ctrl <= fetch_next_md; addr_ctrl <= read_ad; dout_ctrl <= md_lo_dout; next_state <= indirect3_state; -- -- complete idirect addressing -- by loading ea with md -- when indirect3_state => -- load ea with md left_ctrl <= ea_left; right_ctrl <= md_right; alu_ctrl <= alu_ld16; ea_ctrl <= load_ea; -- return to previous state st_ctrl <= pull_st; next_state <= saved_state; -- -- ea holds the low byte of the absolute address -- Move ea low byte into ea high byte -- load new ea low byte to for absolute 16 bit address -- advance the program counter -- when extended_state => -- fetch ea low byte -- increment pc pc_ctrl <= incr_pc; -- fetch next effective address bytes ea_ctrl <= fetch_next_ea; addr_ctrl <= fetch_ad; -- return to previous state st_ctrl <= pull_st; next_state <= saved_state; when lea_state => -- here on load effective address -- load index register with effective address left_ctrl <= pc_left; right_ctrl <= ea_right; alu_ctrl <= alu_lea; case op_code(3 downto 0) is when "0000" => -- leax cc_ctrl <= load_cc; ix_ctrl <= load_ix; when "0001" => -- leay cc_ctrl <= load_cc; iy_ctrl <= load_iy; when "0010" => -- leas sp_ctrl <= load_sp; when "0011" => -- leau up_ctrl <= load_up; when others => null; end case; next_state <= fetch_state; -- -- jump to subroutine -- sp=sp-1 -- call push_return_lo_state to save pc -- return to jmp_state -- when jsr_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; -- call push_return_state st_ctrl <= push_st; return_state <= jmp_state; next_state <= push_return_lo_state; -- -- Load pc with ea -- (JMP) -- when jmp_state => -- load PC with effective address left_ctrl <= pc_left; right_ctrl <= ea_right; alu_ctrl <= alu_ld16; pc_ctrl <= load_pc; next_state <= fetch_state; -- -- long branch or branch to subroutine -- pick up next md byte -- md_hi = md_lo -- md_lo = (pc) -- pc=pc+1 -- if a lbsr push return address -- continue to sbranch_state -- to evaluate conditional branches -- when lbranch_state => pc_ctrl <= incr_pc; -- fetch the next byte into md_lo md_ctrl <= fetch_next_md; addr_ctrl <= fetch_ad; -- if lbsr - push return address -- then continue on to short branch if op_code = "00010111" then st_ctrl <= push_st; return_state <= sbranch_state; next_state <= push_return_lo_state; else next_state <= sbranch_state; end if; -- -- here to execute conditional branch -- short conditional branch md = signed 8 bit offset -- long branch md = 16 bit offset -- when sbranch_state => left_ctrl <= pc_left; right_ctrl <= md_right; alu_ctrl <= alu_add16; -- Test condition for branch if op_code(7 downto 4) = "0010" then -- conditional branch case op_code(3 downto 0) is when "0000" => -- bra cond_true := (1 = 1); when "0001" => -- brn cond_true := (1 = 0); when "0010" => -- bhi cond_true := ((cc(CBIT) or cc(ZBIT)) = '0'); when "0011" => -- bls cond_true := ((cc(CBIT) or cc(ZBIT)) = '1'); when "0100" => -- bcc/bhs cond_true := (cc(CBIT) = '0'); when "0101" => -- bcs/blo cond_true := (cc(CBIT) = '1'); when "0110" => -- bne cond_true := (cc(ZBIT) = '0'); when "0111" => -- beq cond_true := (cc(ZBIT) = '1'); when "1000" => -- bvc cond_true := (cc(VBIT) = '0'); when "1001" => -- bvs cond_true := (cc(VBIT) = '1'); when "1010" => -- bpl cond_true := (cc(NBIT) = '0'); when "1011" => -- bmi cond_true := (cc(NBIT) = '1'); when "1100" => -- bge cond_true := ((cc(NBIT) xor cc(VBIT)) = '0'); when "1101" => -- blt cond_true := ((cc(NBIT) xor cc(VBIT)) = '1'); when "1110" => -- bgt cond_true := ((cc(ZBIT) or (cc(NBIT) xor cc(VBIT))) = '0'); when "1111" => -- ble cond_true := ((cc(ZBIT) or (cc(NBIT) xor cc(VBIT))) = '1'); when others => null; end case; else cond_true := (1 = 1); -- lbra, lbsr, bsr end if; if cond_true then pc_ctrl <= load_pc; end if; next_state <= fetch_state; -- -- push return address onto the S stack -- -- (sp) = pc_lo -- sp = sp - 1 -- when push_return_lo_state => -- decrement the sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; -- write PC low addr_ctrl <= pushs_ad; dout_ctrl <= pc_lo_dout; next_state <= push_return_hi_state; -- -- push program counter hi byte onto the stack -- (sp) = pc_hi -- sp = sp -- return to originating state -- when push_return_hi_state => -- write pc hi bytes addr_ctrl <= pushs_ad; dout_ctrl <= pc_hi_dout; st_ctrl <= pull_st; next_state <= saved_state; when pull_return_hi_state => -- increment the sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- read pc hi pc_ctrl <= pull_hi_pc; addr_ctrl <= pulls_ad; next_state <= pull_return_lo_state; when pull_return_lo_state => -- increment the SP left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- read pc low pc_ctrl <= pull_lo_pc; addr_ctrl <= pulls_ad; dout_ctrl <= pc_lo_dout; -- st_ctrl <= pull_st; next_state <= saved_state; when andcc_state => -- AND CC with md left_ctrl <= md_left; right_ctrl <= zero_right; alu_ctrl <= alu_andcc; cc_ctrl <= load_cc; -- st_ctrl <= pull_st; next_state <= saved_state; when orcc_state => -- OR CC with md left_ctrl <= md_left; right_ctrl <= zero_right; alu_ctrl <= alu_orcc; cc_ctrl <= load_cc; -- st_ctrl <= pull_st; next_state <= saved_state; when tfr_state => -- select source register case md(7 downto 4) is when "0000" => left_ctrl <= accd_left; when "0001" => left_ctrl <= ix_left; when "0010" => left_ctrl <= iy_left; when "0011" => left_ctrl <= up_left; when "0100" => left_ctrl <= sp_left; when "0101" => left_ctrl <= pc_left; when "1000" => left_ctrl <= acca_left; when "1001" => left_ctrl <= accb_left; when "1010" => left_ctrl <= cc_left; when "1011" => left_ctrl <= dp_left; when others => left_ctrl <= md_left; end case; right_ctrl <= zero_right; alu_ctrl <= alu_tfr; -- select destination register case md(3 downto 0) is when "0000" => -- accd acca_ctrl <= load_hi_acca; accb_ctrl <= load_accb; when "0001" => -- ix ix_ctrl <= load_ix; when "0010" => -- iy iy_ctrl <= load_iy; when "0011" => -- up up_ctrl <= load_up; when "0100" => -- sp sp_ctrl <= load_sp; when "0101" => -- pc pc_ctrl <= load_pc; when "1000" => -- acca acca_ctrl <= load_acca; when "1001" => -- accb accb_ctrl <= load_accb; when "1010" => -- cc cc_ctrl <= load_cc; when "1011" => --dp dp_ctrl <= load_dp; when others => null; end case; -- st_ctrl <= pull_st; next_state <= saved_state; when exg_state => -- save destination register case md(3 downto 0) is when "0000" => left_ctrl <= accd_left; when "0001" => left_ctrl <= ix_left; when "0010" => left_ctrl <= iy_left; when "0011" => left_ctrl <= up_left; when "0100" => left_ctrl <= sp_left; when "0101" => left_ctrl <= pc_left; when "1000" => left_ctrl <= acca_left; when "1001" => left_ctrl <= accb_left; when "1010" => left_ctrl <= cc_left; when "1011" => left_ctrl <= dp_left; when others => left_ctrl <= md_left; end case; right_ctrl <= zero_right; alu_ctrl <= alu_tfr; ea_ctrl <= load_ea; -- call tranfer microcode st_ctrl <= push_st; return_state <= exg1_state; next_state <= tfr_state; when exg1_state => -- restore destination left_ctrl <= ea_left; right_ctrl <= zero_right; alu_ctrl <= alu_tfr; -- save as source register case md(7 downto 4) is when "0000" => -- accd acca_ctrl <= load_hi_acca; accb_ctrl <= load_accb; when "0001" => -- ix ix_ctrl <= load_ix; when "0010" => -- iy iy_ctrl <= load_iy; when "0011" => -- up up_ctrl <= load_up; when "0100" => -- sp sp_ctrl <= load_sp; when "0101" => -- pc pc_ctrl <= load_pc; when "1000" => -- acca acca_ctrl <= load_acca; when "1001" => -- accb accb_ctrl <= load_accb; when "1010" => -- cc cc_ctrl <= load_cc; when "1011" => --dp dp_ctrl <= load_dp; when others => null; end case; next_state <= fetch_state; when mul_state => -- move acca to md left_ctrl <= acca_left; right_ctrl <= zero_right; alu_ctrl <= alu_st16; md_ctrl <= load_md; next_state <= mulea_state; when mulea_state => -- move accb to ea left_ctrl <= accb_left; right_ctrl <= zero_right; alu_ctrl <= alu_st16; ea_ctrl <= load_ea; next_state <= muld_state; when muld_state => -- clear accd left_ctrl <= acca_left; right_ctrl <= zero_right; alu_ctrl <= alu_ld8; acca_ctrl <= load_hi_acca; accb_ctrl <= load_accb; next_state <= mul0_state; when mul0_state => -- if bit 0 of ea set, add accd to md left_ctrl <= accd_left; if ea(0) = '1' then right_ctrl <= md_right; else right_ctrl <= zero_right; end if; alu_ctrl <= alu_mul; cc_ctrl <= load_cc; acca_ctrl <= load_hi_acca; accb_ctrl <= load_accb; md_ctrl <= shiftl_md; next_state <= mul1_state; when mul1_state => -- if bit 1 of ea set, add accd to md left_ctrl <= accd_left; if ea(1) = '1' then right_ctrl <= md_right; else right_ctrl <= zero_right; end if; alu_ctrl <= alu_mul; cc_ctrl <= load_cc; acca_ctrl <= load_hi_acca; accb_ctrl <= load_accb; md_ctrl <= shiftl_md; next_state <= mul2_state; when mul2_state => -- if bit 2 of ea set, add accd to md left_ctrl <= accd_left; if ea(2) = '1' then right_ctrl <= md_right; else right_ctrl <= zero_right; end if; alu_ctrl <= alu_mul; cc_ctrl <= load_cc; acca_ctrl <= load_hi_acca; accb_ctrl <= load_accb; md_ctrl <= shiftl_md; next_state <= mul3_state; when mul3_state => -- if bit 3 of ea set, add accd to md left_ctrl <= accd_left; if ea(3) = '1' then right_ctrl <= md_right; else right_ctrl <= zero_right; end if; alu_ctrl <= alu_mul; cc_ctrl <= load_cc; acca_ctrl <= load_hi_acca; accb_ctrl <= load_accb; md_ctrl <= shiftl_md; next_state <= mul4_state; when mul4_state => -- if bit 4 of ea set, add accd to md left_ctrl <= accd_left; if ea(4) = '1' then right_ctrl <= md_right; else right_ctrl <= zero_right; end if; alu_ctrl <= alu_mul; cc_ctrl <= load_cc; acca_ctrl <= load_hi_acca; accb_ctrl <= load_accb; md_ctrl <= shiftl_md; next_state <= mul5_state; when mul5_state => -- if bit 5 of ea set, add accd to md left_ctrl <= accd_left; if ea(5) = '1' then right_ctrl <= md_right; else right_ctrl <= zero_right; end if; alu_ctrl <= alu_mul; cc_ctrl <= load_cc; acca_ctrl <= load_hi_acca; accb_ctrl <= load_accb; md_ctrl <= shiftl_md; next_state <= mul6_state; when mul6_state => -- if bit 6 of ea set, add accd to md left_ctrl <= accd_left; if ea(6) = '1' then right_ctrl <= md_right; else right_ctrl <= zero_right; end if; alu_ctrl <= alu_mul; cc_ctrl <= load_cc; acca_ctrl <= load_hi_acca; accb_ctrl <= load_accb; md_ctrl <= shiftl_md; next_state <= mul7_state; when mul7_state => -- if bit 7 of ea set, add accd to md left_ctrl <= accd_left; if ea(7) = '1' then right_ctrl <= md_right; else right_ctrl <= zero_right; end if; alu_ctrl <= alu_mul; cc_ctrl <= load_cc; acca_ctrl <= load_hi_acca; accb_ctrl <= load_accb; md_ctrl <= shiftl_md; next_state <= fetch_state; -- -- Enter here on pushs -- ea holds post byte -- when pshs_state => -- decrement sp if any registers to be pushed left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; -- idle address addr_ctrl <= idle_ad; dout_ctrl <= cc_dout; if ea(7 downto 0) = "00000000" then sp_ctrl <= latch_sp; else sp_ctrl <= load_sp; end if; if ea(7) = '1' then next_state <= pshs_pcl_state; elsif ea(6) = '1' then next_state <= pshs_upl_state; elsif ea(5) = '1' then next_state <= pshs_iyl_state; elsif ea(4) = '1' then next_state <= pshs_ixl_state; elsif ea(3) = '1' then next_state <= pshs_dp_state; elsif ea(2) = '1' then next_state <= pshs_accb_state; elsif ea(1) = '1' then next_state <= pshs_acca_state; elsif ea(0) = '1' then next_state <= pshs_cc_state; else next_state <= fetch_state; end if; when pshs_pcl_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; -- write pc low addr_ctrl <= pushs_ad; dout_ctrl <= pc_lo_dout; next_state <= pshs_pch_state; when pshs_pch_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; if ea(6 downto 0) = "0000000" then sp_ctrl <= latch_sp; else sp_ctrl <= load_sp; end if; -- write pc hi addr_ctrl <= pushs_ad; dout_ctrl <= pc_hi_dout; if ea(6) = '1' then next_state <= pshs_upl_state; elsif ea(5) = '1' then next_state <= pshs_iyl_state; elsif ea(4) = '1' then next_state <= pshs_ixl_state; elsif ea(3) = '1' then next_state <= pshs_dp_state; elsif ea(2) = '1' then next_state <= pshs_accb_state; elsif ea(1) = '1' then next_state <= pshs_acca_state; elsif ea(0) = '1' then next_state <= pshs_cc_state; else next_state <= fetch_state; end if; when pshs_upl_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; -- write pc low addr_ctrl <= pushs_ad; dout_ctrl <= up_lo_dout; next_state <= pshs_uph_state; when pshs_uph_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; if ea(5 downto 0) = "000000" then sp_ctrl <= latch_sp; else sp_ctrl <= load_sp; end if; -- write pc hi addr_ctrl <= pushs_ad; dout_ctrl <= up_hi_dout; if ea(5) = '1' then next_state <= pshs_iyl_state; elsif ea(4) = '1' then next_state <= pshs_ixl_state; elsif ea(3) = '1' then next_state <= pshs_dp_state; elsif ea(2) = '1' then next_state <= pshs_accb_state; elsif ea(1) = '1' then next_state <= pshs_acca_state; elsif ea(0) = '1' then next_state <= pshs_cc_state; else next_state <= fetch_state; end if; when pshs_iyl_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; -- write iy low addr_ctrl <= pushs_ad; dout_ctrl <= iy_lo_dout; next_state <= pshs_iyh_state; when pshs_iyh_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; if ea(4 downto 0) = "00000" then sp_ctrl <= latch_sp; else sp_ctrl <= load_sp; end if; -- write iy hi addr_ctrl <= pushs_ad; dout_ctrl <= iy_hi_dout; if ea(4) = '1' then next_state <= pshs_ixl_state; elsif ea(3) = '1' then next_state <= pshs_dp_state; elsif ea(2) = '1' then next_state <= pshs_accb_state; elsif ea(1) = '1' then next_state <= pshs_acca_state; elsif ea(0) = '1' then next_state <= pshs_cc_state; else next_state <= fetch_state; end if; when pshs_ixl_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; -- write ix low addr_ctrl <= pushs_ad; dout_ctrl <= ix_lo_dout; next_state <= pshs_ixh_state; when pshs_ixh_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; if ea(3 downto 0) = "0000" then sp_ctrl <= latch_sp; else sp_ctrl <= load_sp; end if; -- write ix hi addr_ctrl <= pushs_ad; dout_ctrl <= ix_hi_dout; if ea(3) = '1' then next_state <= pshs_dp_state; elsif ea(2) = '1' then next_state <= pshs_accb_state; elsif ea(1) = '1' then next_state <= pshs_acca_state; elsif ea(0) = '1' then next_state <= pshs_cc_state; else next_state <= fetch_state; end if; when pshs_dp_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; if ea(2 downto 0) = "000" then sp_ctrl <= latch_sp; else sp_ctrl <= load_sp; end if; -- write dp addr_ctrl <= pushs_ad; dout_ctrl <= dp_dout; if ea(2) = '1' then next_state <= pshs_accb_state; elsif ea(1) = '1' then next_state <= pshs_acca_state; elsif ea(0) = '1' then next_state <= pshs_cc_state; else next_state <= fetch_state; end if; when pshs_accb_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; if ea(1 downto 0) = "00" then sp_ctrl <= latch_sp; else sp_ctrl <= load_sp; end if; -- write accb addr_ctrl <= pushs_ad; dout_ctrl <= accb_dout; if ea(1) = '1' then next_state <= pshs_acca_state; elsif ea(0) = '1' then next_state <= pshs_cc_state; else next_state <= fetch_state; end if; when pshs_acca_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; if ea(0) = '1' then sp_ctrl <= load_sp; else sp_ctrl <= latch_sp; end if; -- write acca addr_ctrl <= pushs_ad; dout_ctrl <= acca_dout; if ea(0) = '1' then next_state <= pshs_cc_state; else next_state <= fetch_state; end if; when pshs_cc_state => -- idle sp -- write cc addr_ctrl <= pushs_ad; dout_ctrl <= cc_dout; next_state <= fetch_state; -- -- enter here on PULS -- ea hold register mask -- when puls_state => if ea(0) = '1' then next_state <= puls_cc_state; elsif ea(1) = '1' then next_state <= puls_acca_state; elsif ea(2) = '1' then next_state <= puls_accb_state; elsif ea(3) = '1' then next_state <= puls_dp_state; elsif ea(4) = '1' then next_state <= puls_ixh_state; elsif ea(5) = '1' then next_state <= puls_iyh_state; elsif ea(6) = '1' then next_state <= puls_uph_state; elsif ea(7) = '1' then next_state <= puls_pch_state; else next_state <= fetch_state; end if; when puls_cc_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- read cc cc_ctrl <= pull_cc; addr_ctrl <= pulls_ad; if ea(1) = '1' then next_state <= puls_acca_state; elsif ea(2) = '1' then next_state <= puls_accb_state; elsif ea(3) = '1' then next_state <= puls_dp_state; elsif ea(4) = '1' then next_state <= puls_ixh_state; elsif ea(5) = '1' then next_state <= puls_iyh_state; elsif ea(6) = '1' then next_state <= puls_uph_state; elsif ea(7) = '1' then next_state <= puls_pch_state; else next_state <= fetch_state; end if; when puls_acca_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- read acca acca_ctrl <= pull_acca; addr_ctrl <= pulls_ad; if ea(2) = '1' then next_state <= puls_accb_state; elsif ea(3) = '1' then next_state <= puls_dp_state; elsif ea(4) = '1' then next_state <= puls_ixh_state; elsif ea(5) = '1' then next_state <= puls_iyh_state; elsif ea(6) = '1' then next_state <= puls_uph_state; elsif ea(7) = '1' then next_state <= puls_pch_state; else next_state <= fetch_state; end if; when puls_accb_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- read accb accb_ctrl <= pull_accb; addr_ctrl <= pulls_ad; if ea(3) = '1' then next_state <= puls_dp_state; elsif ea(4) = '1' then next_state <= puls_ixh_state; elsif ea(5) = '1' then next_state <= puls_iyh_state; elsif ea(6) = '1' then next_state <= puls_uph_state; elsif ea(7) = '1' then next_state <= puls_pch_state; else next_state <= fetch_state; end if; when puls_dp_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- read dp dp_ctrl <= pull_dp; addr_ctrl <= pulls_ad; if ea(4) = '1' then next_state <= puls_ixh_state; elsif ea(5) = '1' then next_state <= puls_iyh_state; elsif ea(6) = '1' then next_state <= puls_uph_state; elsif ea(7) = '1' then next_state <= puls_pch_state; else next_state <= fetch_state; end if; when puls_ixh_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- pull ix hi ix_ctrl <= pull_hi_ix; addr_ctrl <= pulls_ad; next_state <= puls_ixl_state; when puls_ixl_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- read ix low ix_ctrl <= pull_lo_ix; addr_ctrl <= pulls_ad; if ea(5) = '1' then next_state <= puls_iyh_state; elsif ea(6) = '1' then next_state <= puls_uph_state; elsif ea(7) = '1' then next_state <= puls_pch_state; else next_state <= fetch_state; end if; when puls_iyh_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- pull iy hi iy_ctrl <= pull_hi_iy; addr_ctrl <= pulls_ad; next_state <= puls_iyl_state; when puls_iyl_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- read iy low iy_ctrl <= pull_lo_iy; addr_ctrl <= pulls_ad; if ea(6) = '1' then next_state <= puls_uph_state; elsif ea(7) = '1' then next_state <= puls_pch_state; else next_state <= fetch_state; end if; when puls_uph_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- pull up hi up_ctrl <= pull_hi_up; addr_ctrl <= pulls_ad; next_state <= puls_upl_state; when puls_upl_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- read up low up_ctrl <= pull_lo_up; addr_ctrl <= pulls_ad; if ea(7) = '1' then next_state <= puls_pch_state; else next_state <= fetch_state; end if; when puls_pch_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- pull pc hi pc_ctrl <= pull_hi_pc; addr_ctrl <= pulls_ad; next_state <= puls_pcl_state; when puls_pcl_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- read pc low pc_ctrl <= pull_lo_pc; addr_ctrl <= pulls_ad; next_state <= fetch_state; -- -- Enter here on pshu -- ea holds post byte -- when pshu_state => -- decrement up if any registers to be pushed left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; if ea(7 downto 0) = "00000000" then up_ctrl <= latch_up; else up_ctrl <= load_up; end if; -- write idle bus if ea(7) = '1' then next_state <= pshu_pcl_state; elsif ea(6) = '1' then next_state <= pshu_spl_state; elsif ea(5) = '1' then next_state <= pshu_iyl_state; elsif ea(4) = '1' then next_state <= pshu_ixl_state; elsif ea(3) = '1' then next_state <= pshu_dp_state; elsif ea(2) = '1' then next_state <= pshu_accb_state; elsif ea(1) = '1' then next_state <= pshu_acca_state; elsif ea(0) = '1' then next_state <= pshu_cc_state; else next_state <= fetch_state; end if; -- -- push PC onto U stack -- when pshu_pcl_state => -- decrement up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; up_ctrl <= load_up; -- write pc low addr_ctrl <= pushu_ad; dout_ctrl <= pc_lo_dout; next_state <= pshu_pch_state; when pshu_pch_state => -- decrement up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; if ea(6 downto 0) = "0000000" then up_ctrl <= latch_up; else up_ctrl <= load_up; end if; -- write pc hi addr_ctrl <= pushu_ad; dout_ctrl <= pc_hi_dout; if ea(6) = '1' then next_state <= pshu_spl_state; elsif ea(5) = '1' then next_state <= pshu_iyl_state; elsif ea(4) = '1' then next_state <= pshu_ixl_state; elsif ea(3) = '1' then next_state <= pshu_dp_state; elsif ea(2) = '1' then next_state <= pshu_accb_state; elsif ea(1) = '1' then next_state <= pshu_acca_state; elsif ea(0) = '1' then next_state <= pshu_cc_state; else next_state <= fetch_state; end if; when pshu_spl_state => -- decrement up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; up_ctrl <= load_up; -- write sp low addr_ctrl <= pushu_ad; dout_ctrl <= sp_lo_dout; next_state <= pshu_sph_state; when pshu_sph_state => -- decrement up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; if ea(5 downto 0) = "000000" then up_ctrl <= latch_up; else up_ctrl <= load_up; end if; -- write sp hi addr_ctrl <= pushu_ad; dout_ctrl <= sp_hi_dout; if ea(5) = '1' then next_state <= pshu_iyl_state; elsif ea(4) = '1' then next_state <= pshu_ixl_state; elsif ea(3) = '1' then next_state <= pshu_dp_state; elsif ea(2) = '1' then next_state <= pshu_accb_state; elsif ea(1) = '1' then next_state <= pshu_acca_state; elsif ea(0) = '1' then next_state <= pshu_cc_state; else next_state <= fetch_state; end if; when pshu_iyl_state => -- decrement up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; up_ctrl <= load_up; -- write iy low addr_ctrl <= pushu_ad; dout_ctrl <= iy_lo_dout; next_state <= pshu_iyh_state; when pshu_iyh_state => -- decrement up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; if ea(4 downto 0) = "00000" then up_ctrl <= latch_up; else up_ctrl <= load_up; end if; -- write iy hi addr_ctrl <= pushu_ad; dout_ctrl <= iy_hi_dout; if ea(4) = '1' then next_state <= pshu_ixl_state; elsif ea(3) = '1' then next_state <= pshu_dp_state; elsif ea(2) = '1' then next_state <= pshu_accb_state; elsif ea(1) = '1' then next_state <= pshu_acca_state; elsif ea(0) = '1' then next_state <= pshu_cc_state; else next_state <= fetch_state; end if; when pshu_ixl_state => -- decrement up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; up_ctrl <= load_up; -- write ix low addr_ctrl <= pushu_ad; dout_ctrl <= ix_lo_dout; next_state <= pshu_ixh_state; when pshu_ixh_state => -- decrement up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; if ea(3 downto 0) = "0000" then up_ctrl <= latch_up; else up_ctrl <= load_up; end if; -- write ix hi addr_ctrl <= pushu_ad; dout_ctrl <= ix_hi_dout; if ea(3) = '1' then next_state <= pshu_dp_state; elsif ea(2) = '1' then next_state <= pshu_accb_state; elsif ea(1) = '1' then next_state <= pshu_acca_state; elsif ea(0) = '1' then next_state <= pshu_cc_state; else next_state <= fetch_state; end if; when pshu_dp_state => -- decrement up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; if ea(2 downto 0) = "000" then up_ctrl <= latch_up; else up_ctrl <= load_up; end if; -- write dp addr_ctrl <= pushu_ad; dout_ctrl <= dp_dout; if ea(2) = '1' then next_state <= pshu_accb_state; elsif ea(1) = '1' then next_state <= pshu_acca_state; elsif ea(0) = '1' then next_state <= pshu_cc_state; else next_state <= fetch_state; end if; when pshu_accb_state => -- decrement up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; if ea(1 downto 0) = "00" then up_ctrl <= latch_up; else up_ctrl <= load_up; end if; -- write accb addr_ctrl <= pushu_ad; dout_ctrl <= accb_dout; if ea(1) = '1' then next_state <= pshu_acca_state; elsif ea(0) = '1' then next_state <= pshu_cc_state; else next_state <= fetch_state; end if; when pshu_acca_state => -- decrement up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; if ea(0) = '0' then up_ctrl <= latch_up; else up_ctrl <= load_up; end if; -- write acca addr_ctrl <= pushu_ad; dout_ctrl <= acca_dout; if ea(0) = '1' then next_state <= pshu_cc_state; else next_state <= fetch_state; end if; when pshu_cc_state => -- idle up -- write cc addr_ctrl <= pushu_ad; dout_ctrl <= cc_dout; next_state <= fetch_state; -- -- enter here on PULU -- ea hold register mask -- when pulu_state => -- idle UP -- idle bus if ea(0) = '1' then next_state <= pulu_cc_state; elsif ea(1) = '1' then next_state <= pulu_acca_state; elsif ea(2) = '1' then next_state <= pulu_accb_state; elsif ea(3) = '1' then next_state <= pulu_dp_state; elsif ea(4) = '1' then next_state <= pulu_ixh_state; elsif ea(5) = '1' then next_state <= pulu_iyh_state; elsif ea(6) = '1' then next_state <= pulu_sph_state; elsif ea(7) = '1' then next_state <= pulu_pch_state; else next_state <= fetch_state; end if; when pulu_cc_state => -- increment up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; up_ctrl <= load_up; -- read cc cc_ctrl <= pull_cc; addr_ctrl <= pullu_ad; if ea(1) = '1' then next_state <= pulu_acca_state; elsif ea(2) = '1' then next_state <= pulu_accb_state; elsif ea(3) = '1' then next_state <= pulu_dp_state; elsif ea(4) = '1' then next_state <= pulu_ixh_state; elsif ea(5) = '1' then next_state <= pulu_iyh_state; elsif ea(6) = '1' then next_state <= pulu_sph_state; elsif ea(7) = '1' then next_state <= pulu_pch_state; else next_state <= fetch_state; end if; when pulu_acca_state => -- increment up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; up_ctrl <= load_up; -- read acca acca_ctrl <= pull_acca; addr_ctrl <= pullu_ad; if ea(2) = '1' then next_state <= pulu_accb_state; elsif ea(3) = '1' then next_state <= pulu_dp_state; elsif ea(4) = '1' then next_state <= pulu_ixh_state; elsif ea(5) = '1' then next_state <= pulu_iyh_state; elsif ea(6) = '1' then next_state <= pulu_sph_state; elsif ea(7) = '1' then next_state <= pulu_pch_state; else next_state <= fetch_state; end if; when pulu_accb_state => -- increment up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; up_ctrl <= load_up; -- read accb accb_ctrl <= pull_accb; addr_ctrl <= pullu_ad; if ea(3) = '1' then next_state <= pulu_dp_state; elsif ea(4) = '1' then next_state <= pulu_ixh_state; elsif ea(5) = '1' then next_state <= pulu_iyh_state; elsif ea(6) = '1' then next_state <= pulu_sph_state; elsif ea(7) = '1' then next_state <= pulu_pch_state; else next_state <= fetch_state; end if; when pulu_dp_state => -- increment up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; up_ctrl <= load_up; -- read dp dp_ctrl <= pull_dp; addr_ctrl <= pullu_ad; if ea(4) = '1' then next_state <= pulu_ixh_state; elsif ea(5) = '1' then next_state <= pulu_iyh_state; elsif ea(6) = '1' then next_state <= pulu_sph_state; elsif ea(7) = '1' then next_state <= pulu_pch_state; else next_state <= fetch_state; end if; when pulu_ixh_state => -- increment up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; up_ctrl <= load_up; -- read ix hi ix_ctrl <= pull_hi_ix; addr_ctrl <= pullu_ad; next_state <= pulu_ixl_state; when pulu_ixl_state => -- increment up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; up_ctrl <= load_up; -- read ix low ix_ctrl <= pull_lo_ix; addr_ctrl <= pullu_ad; if ea(5) = '1' then next_state <= pulu_iyh_state; elsif ea(6) = '1' then next_state <= pulu_sph_state; elsif ea(7) = '1' then next_state <= pulu_pch_state; else next_state <= fetch_state; end if; when pulu_iyh_state => -- increment up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; up_ctrl <= load_up; -- read iy hi iy_ctrl <= pull_hi_iy; addr_ctrl <= pullu_ad; next_state <= pulu_iyl_state; when pulu_iyl_state => -- increment up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; up_ctrl <= load_up; -- read iy low iy_ctrl <= pull_lo_iy; addr_ctrl <= pullu_ad; if ea(6) = '1' then next_state <= pulu_sph_state; elsif ea(7) = '1' then next_state <= pulu_pch_state; else next_state <= fetch_state; end if; when pulu_sph_state => -- increment up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; up_ctrl <= load_up; -- read sp hi sp_ctrl <= pull_hi_sp; addr_ctrl <= pullu_ad; next_state <= pulu_spl_state; when pulu_spl_state => -- increment up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; up_ctrl <= load_up; -- read sp low sp_ctrl <= pull_lo_sp; addr_ctrl <= pullu_ad; if ea(7) = '1' then next_state <= pulu_pch_state; else next_state <= fetch_state; end if; when pulu_pch_state => -- increment up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; up_ctrl <= load_up; -- pull pc hi pc_ctrl <= pull_hi_pc; addr_ctrl <= pullu_ad; next_state <= pulu_pcl_state; when pulu_pcl_state => -- increment up left_ctrl <= up_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; up_ctrl <= load_up; -- read pc low pc_ctrl <= pull_lo_pc; addr_ctrl <= pullu_ad; next_state <= fetch_state; -- -- pop the Condition codes -- when rti_cc_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- read cc cc_ctrl <= pull_cc; addr_ctrl <= pulls_ad; next_state <= rti_entire_state; -- -- Added RTI cycle 11th July 2006 John Kent. -- test the "Entire" Flag -- that has just been popped off the stack -- when rti_entire_state => -- -- The Entire flag must be recovered from the stack -- before testing. -- if cc(EBIT) = '1' then next_state <= rti_acca_state; else next_state <= rti_pch_state; end if; when rti_acca_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- read acca acca_ctrl <= pull_acca; addr_ctrl <= pulls_ad; next_state <= rti_accb_state; when rti_accb_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- read accb accb_ctrl <= pull_accb; addr_ctrl <= pulls_ad; next_state <= rti_dp_state; when rti_dp_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- read dp dp_ctrl <= pull_dp; addr_ctrl <= pulls_ad; next_state <= rti_ixh_state; when rti_ixh_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- read ix hi ix_ctrl <= pull_hi_ix; addr_ctrl <= pulls_ad; next_state <= rti_ixl_state; when rti_ixl_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- read ix low ix_ctrl <= pull_lo_ix; addr_ctrl <= pulls_ad; next_state <= rti_iyh_state; when rti_iyh_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- read iy hi iy_ctrl <= pull_hi_iy; addr_ctrl <= pulls_ad; next_state <= rti_iyl_state; when rti_iyl_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- read iy low iy_ctrl <= pull_lo_iy; addr_ctrl <= pulls_ad; next_state <= rti_uph_state; when rti_uph_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- read up hi up_ctrl <= pull_hi_up; addr_ctrl <= pulls_ad; next_state <= rti_upl_state; when rti_upl_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- read up low up_ctrl <= pull_lo_up; addr_ctrl <= pulls_ad; next_state <= rti_pch_state; when rti_pch_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- pull pc hi pc_ctrl <= pull_hi_pc; addr_ctrl <= pulls_ad; next_state <= rti_pcl_state; when rti_pcl_state => -- increment sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_add16; sp_ctrl <= load_sp; -- pull pc low pc_ctrl <= pull_lo_pc; addr_ctrl <= pulls_ad; next_state <= fetch_state; -- -- here on IRQ or NMI interrupt -- pre decrement the sp -- Idle bus cycle -- when int_nmiirq_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; next_state <= int_entire_state; -- -- set Entire Flag on SWI, SWI2, SWI3 and CWAI, IRQ and NMI -- clear Entire Flag on FIRQ -- before stacking all registers -- when int_entire_state => -- set entire flag alu_ctrl <= alu_see; cc_ctrl <= load_cc; next_state <= int_pcl_state; -- -- here on FIRQ interrupt -- pre decrement the sp -- Idle bus cycle -- when int_firq_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; next_state <= int_fast_state; -- -- clear Entire Flag on FIRQ -- before stacking all registers -- when int_fast_state => -- clear entire flag alu_ctrl <= alu_cle; cc_ctrl <= load_cc; next_state <= int_pcl_state; when int_pcl_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; -- write pc low addr_ctrl <= pushs_ad; dout_ctrl <= pc_lo_dout; next_state <= int_pch_state; when int_pch_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; -- write pc hi addr_ctrl <= pushs_ad; dout_ctrl <= pc_hi_dout; if cc(EBIT) = '1' then next_state <= int_upl_state; else next_state <= int_cc_state; end if; when int_upl_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; -- write up low addr_ctrl <= pushs_ad; dout_ctrl <= up_lo_dout; next_state <= int_uph_state; when int_uph_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; -- write ix hi addr_ctrl <= pushs_ad; dout_ctrl <= up_hi_dout; next_state <= int_iyl_state; when int_iyl_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; -- write ix low addr_ctrl <= pushs_ad; dout_ctrl <= iy_lo_dout; next_state <= int_iyh_state; when int_iyh_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; -- write ix hi addr_ctrl <= pushs_ad; dout_ctrl <= iy_hi_dout; next_state <= int_ixl_state; when int_ixl_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; -- write ix low addr_ctrl <= pushs_ad; dout_ctrl <= ix_lo_dout; next_state <= int_ixh_state; when int_ixh_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; -- write ix hi addr_ctrl <= pushs_ad; dout_ctrl <= ix_hi_dout; next_state <= int_dp_state; when int_dp_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; -- write accb addr_ctrl <= pushs_ad; dout_ctrl <= dp_dout; next_state <= int_accb_state; when int_accb_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; -- write accb addr_ctrl <= pushs_ad; dout_ctrl <= accb_dout; next_state <= int_acca_state; when int_acca_state => -- decrement sp left_ctrl <= sp_left; right_ctrl <= one_right; alu_ctrl <= alu_sub16; sp_ctrl <= load_sp; -- write acca addr_ctrl <= pushs_ad; dout_ctrl <= acca_dout; next_state <= int_cc_state; when int_cc_state => -- write cc addr_ctrl <= pushs_ad; dout_ctrl <= cc_dout; case iv is when NMI_VEC => next_state <= int_maskif_state; when SWI_VEC => next_state <= int_maskif_state; when FIRQ_VEC => next_state <= int_maskif_state; when IRQ_VEC => next_state <= int_maski_state; when SWI2_VEC => next_state <= vect_hi_state; when SWI3_VEC => next_state <= vect_hi_state; when others => if op_code = "00111100" then -- CWAI next_state <= int_cwai_state; else next_state <= rti_cc_state; -- spurious interrupt, do a RTI end if; end case; -- -- wait here for an inteerupt -- when int_cwai_state => if (nmi_req = '1') and (nmi_ack='0') then iv_ctrl <= nmi_iv; nmi_ctrl <= set_nmi; next_state <= int_maskif_state; else -- -- nmi request is not cleared until nmi input goes low -- if (nmi_req = '0') and (nmi_ack='1') then nmi_ctrl <= reset_nmi; end if; -- -- FIRQ is level sensitive -- if (firq = '1') and (cc(FBIT) = '0') then iv_ctrl <= firq_iv; next_state <= int_maskif_state; -- -- IRQ is level sensitive -- elsif (irq = '1') and (cc(IBIT) = '0') then iv_ctrl <= irq_iv; next_state <= int_maski_state; else iv_ctrl <= reset_iv; next_state <= int_cwai_state; end if; end if; when int_maski_state => alu_ctrl <= alu_sei; cc_ctrl <= load_cc; next_state <= vect_hi_state; when int_maskif_state => alu_ctrl <= alu_seif; cc_ctrl <= load_cc; next_state <= vect_hi_state; -- -- According to the 6809 programming manual: -- If an interrupt is received and is masked -- or lasts for less than three cycles, the PC -- will advance to the next instruction. -- If an interrupt is unmasked and lasts -- for more than three cycles, an interrupt -- will be generated. -- Note that I don't wait 3 clock cycles. -- John Kent 11th July 2006 -- when sync_state => if (nmi_req = '1') and (nmi_ack='0') then iv_ctrl <= nmi_iv; nmi_ctrl <= set_nmi; next_state <= int_nmiirq_state; else -- -- nmi request is not cleared until nmi input goes low -- if (nmi_req = '0') and (nmi_ack='1') then iv_ctrl <= reset_iv; nmi_ctrl <= reset_nmi; end if; -- -- FIRQ is level sensitive -- if (firq = '1') then if (cc(FBIT) = '0') then iv_ctrl <= firq_iv; next_state <= int_firq_state; else iv_ctrl <= reset_iv; next_state <= fetch_state; end if; -- -- IRQ is level sensitive -- elsif (irq = '1') then if (cc(IBIT) = '0') then iv_ctrl <= irq_iv; next_state <= int_nmiirq_state; else iv_ctrl <= reset_iv; next_state <= fetch_state; end if; else iv_ctrl <= reset_iv; next_state <= sync_state; end if; end if; when halt_state => if halt = '1' then next_state <= halt_state; else next_state <= fetch_state; end if; when others => -- halt on undefine states next_state <= error_state; end case; end process; end rtl;
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