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https://opencores.org/ocsvn/ion/ion/trunk
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- This comparison shows the changes necessary to convert path
/ion
- from Rev 152 to Rev 153
- ↔ Reverse comparison
Rev 152 → Rev 153
/trunk/vhdl/mips_cpu.vhdl
4,23 → 4,19
-- project: ION (http://www.opencores.org/project,ion_cpu) |
-- author: Jose A. Ruiz (ja_rd@hotmail.com) |
-- created: Jan/11/2011 |
-- last modified: Apr/13/2011 (ja_rd@hotmail.com) |
-- last modified: Jun/05/2011 (ja_rd@hotmail.com) |
-------------------------------------------------------------------------------- |
-- Use under the terms of the GPL. |
-- Software 'as is' without warranty. Author liable for nothing. |
-- |
-------------------------------------------------------------------------------- |
-- Please read file /doc/ion_project.txt for usage instructions. |
-------------------------------------------------------------------------------- |
--### MIPS-I things not implemented |
-- # Invalid instruction trapping: |
-- * invalid opcodes do trap but the logic that prevents bad opcodes from |
-- having side affects has not been tested yet. |
-- # Kernel/user status |
-- # RTE instruction (or ERET) |
-- # Most of the CP0 registers and of course all of the CP1 |
-- # External interrupts |
-- |
--### Things implemented but not tested |
-- # Memory pause input -- only tested with stub cache |
-- 1.- RTE instruction (or ERET) missing, with CP0.SR KUo/IEo & KUP/IEp flags. |
-- 2.- Most of the R3000 CP0 registers and of course all of the CP1. |
-- 3.- External interrupts missing, with CP0.SR IR, NMI and IM7..0 flags. |
-- |
--### Things with provisional implementation |
-- |
28,6 → 24,16
-- if the target register is not used in the following instruction. So that |
-- every load takes two cycles. |
-- The interlock logic should check register indices (@note2) |
-- 2.- CP0 SR (status register) bits KUo/IEo & KUP/IEp are missing. |
-- This means that EXCEPTIONS CAN'T BE NESTED in this version of the CPU. |
-- 3.- Invalid instruction side effects: |
-- Invalid opcodes do trap but the logic that prevents bad opcodes from |
-- having side affects has not been tested yet. |
-- 4.- Kernel/user status. |
-- When in user mode, COP* instructions will trigger a 'CpU' exception. |
-- BUT there's no address checking and user code can still access kernel |
-- space in this version. |
-- Besides, see point 2 above about the missing SR bits. |
-- |
-------------------------------------------------------------------------------- |
|
137,8 → 143,11
signal p1_exception : std_logic; |
signal p1_do_reg_jump : std_logic; |
signal p1_do_zero_ext_imm : std_logic; |
signal p1_set_cp : std_logic; |
signal p1_get_cp : std_logic; |
signal p1_set_cp0 : std_logic; |
signal p1_get_cp0 : std_logic; |
signal p1_rfe : std_logic; |
signal p1_alu_op2_sel : std_logic_vector(1 downto 0); |
signal p1_alu_op2_sel_set0: std_logic_vector(1 downto 0); |
signal p1_alu_op2_sel_set1: std_logic_vector(1 downto 0); |
165,6 → 174,7
signal p1_muldiv_stall : std_logic; |
|
signal p1_unknown_opcode : std_logic; |
signal p1_cp_unavailable : std_logic; |
|
-------------------------------------------------------------------------------- |
-- Pipeline stage 2 |
201,8 → 211,8
-------------------------------------------------------------------------------- |
-- CP0 registers and signals |
|
-- CP0[12]: status register |
signal cp0_status : std_logic_vector(1 downto 0); |
-- CP0[12]: status register, KUo/IEo & KUP/IEp & KU/IE bits |
signal cp0_status : std_logic_vector(5 downto 0); |
-- CP0[12]: status register, cache control |
signal cp0_cache_control : std_logic_vector(17 downto 16); |
-- Output of CP0 register bank (only a few regs are implemented) |
593,14 → 603,25
|
-- Decode instructions that launch exceptions |
p1_exception <= '1' when |
(p1_op_special='1' and p1_ir_reg(5 downto 1)="00110") or |
p1_unknown_opcode='1' |
(p1_op_special='1' and p1_ir_reg(5 downto 1)="00110") or -- syscall/break |
p1_unknown_opcode='1' or |
p1_cp_unavailable='1' |
else '0'; |
|
-- Decode MTC0/MFC0 instructions |
p1_set_cp0 <= '1' when p1_ir_reg(31 downto 21)="01000000100" else '0'; |
p1_get_cp0 <= '1' when p1_ir_reg(31 downto 21)="01000000000" else '0'; |
-- Decode MTC0/MFC0 instructions (see @note3) |
p1_set_cp <= '1' when p1_ir_reg(31 downto 28)="0100" and |
p1_ir_reg(25 downto 21)="00100" else '0'; |
p1_get_cp <= '1' when p1_ir_reg(31 downto 28)="0100" and |
p1_ir_reg(25 downto 21)="00000" else '0'; |
|
p1_set_cp0 <= '1' when p1_ir_reg(27 downto 26)="00" and p1_set_cp='1' else '0'; |
p1_get_cp0 <= '1' when p1_ir_reg(27 downto 26)="00" and p1_get_cp='1' else '0'; |
|
-- Decode RFE instruction (see @note3) |
p1_rfe <= '1' when p1_ir_reg(31 downto 21)="01000010000" and |
p1_ir_reg(5 downto 0)="010000" |
else '0'; |
|
-- Raise some signals for some particular group of opcodes |
p1_op_special <= '1' when p1_ir_op="000000" else '0'; -- group '0' opcodes |
p1_do_reg_jump <= '1' when p1_op_special='1' and p1_ir_fn(5 downto 1)="00100" else '0'; |
768,6 → 789,13
|
else '0'; |
|
p1_cp_unavailable <= '1' when |
(p1_set_cp='1' and p1_set_cp0='0') or -- mtc1..3 |
(p1_get_cp='1' and p1_get_cp0='0') or -- mfc1..3 |
((p1_get_cp0='1' or p1_set_cp0='1' or p1_rfe='1') |
and cp0_status(1)='0') -- COP0 user mode |
else '0'; |
|
--############################################################################## |
-- Pipeline registers & pipeline control logic |
|
999,43 → 1027,67
|
|
--############################################################################## |
-- CP0 (what little is implemented of it) |
-- CP0 and exception processing |
|
cp0_registers: |
process(clk) |
begin |
if clk'event and clk='1' then |
if reset='1' then |
-- "10" => mode=kernel; ints=disabled |
cp0_status <= "10"; |
-- KU/IE="10" ==> mode=kernel; ints=disabled |
cp0_status <= "000010"; -- bits (KUo/IEo & KUp/IEp) reset to zero |
cp0_cache_control <= "00"; |
cp0_cause_exc_code <= "00000"; |
cp0_cause_bd <= '0'; |
else |
-- no need to check for stall cycles when loading these |
if p1_set_cp0='1' then |
-- NOTE: in MTCx, the source register is Rt |
-- FIXME check for CP0 reg index |
cp0_status <= p1_rt(cp0_status'high downto 0); |
cp0_cache_control <= p1_rt(17 downto 16); |
end if; |
if p1_exception='1' and pipeline_stalled='0' then |
cp0_epc <= p0_pc_restart; |
if pipeline_stalled='0' then |
if p1_exception='1' then |
-- Exception: do all that needs to be done right here |
|
if p1_unknown_opcode='1' then |
cp0_cause_exc_code <= "01010"; -- bad opcode |
else |
if p1_ir_fn(0)='0' then |
cp0_cause_exc_code <= "01000"; -- syscall |
-- Save PC in EPC register... |
cp0_epc <= p0_pc_restart; |
-- ... set KU flag to Kernel mode ... |
cp0_status(1) <= '1'; |
-- ... and 'push' old KU/IE flag values |
cp0_status(5 downto 4) <= cp0_status(3 downto 2); |
cp0_status(3 downto 2) <= cp0_status(1 downto 0); |
|
-- Set the 'exception cause' code... |
if p1_unknown_opcode='1' then |
cp0_cause_exc_code <= "01010"; -- bad opcode ('reserved') |
elsif p1_cp_unavailable='1' then |
-- this triggers for mtc0/mfc0 in user mode too |
cp0_cause_exc_code <= "01011"; -- CP* unavailable |
else |
cp0_cause_exc_code <= "01001"; -- break |
if p1_ir_fn(0)='0' then |
cp0_cause_exc_code <= "01000"; -- syscall |
else |
cp0_cause_exc_code <= "01001"; -- break |
end if; |
end if; |
-- ... and the BD flag for exceptions in delay slots |
cp0_cause_bd <= cp0_in_delay_slot; |
|
-- FIXME RFE missing |
elsif p1_rfe='1' and cp0_status(1)='1' then |
-- RFE: restore ('pop') the KU/IE flag values |
|
cp0_status(3 downto 2) <= cp0_status(5 downto 4); |
cp0_status(1 downto 0) <= cp0_status(3 downto 2); |
|
elsif p1_set_cp0='1' and cp0_status(1)='1' then |
-- MTC0: load CP0[xx] with Rt |
|
-- NOTE: in MTCx, the source register is Rt |
-- FIXME this works because only SR is writeable; when |
-- CP0[13].IP1-0 are implemented, check for CP0 reg index. |
cp0_status <= p1_rt(cp0_status'high downto 0); |
cp0_cache_control <= p1_rt(17 downto 16); |
end if; |
|
cp0_cause_bd <= cp0_in_delay_slot; |
end if; |
end if; |
end if; |
end process; |
end process cp0_registers; |
|
cache_enable <= cp0_cache_control(17); |
ic_invalidate <= cp0_cache_control(16); |
1042,12 → 1094,11
|
cp0_cause_ce <= "00"; -- FIXME CP* traps merged with unimplemented opcode traps |
cp0_cause <= cp0_cause_bd & '0' & cp0_cause_ce & |
X"00000" & "000" & |
cp0_cause_exc_code; |
X"00000" & '0' & cp0_cause_exc_code & "00"; |
|
-- FIXME the mux should mask to zero for any unused reg index |
with p1_c0_rs_num select cp0_reg_read <= |
X"0000000" & "00" & cp0_status when "01100", |
X"000000" & "00" & cp0_status when "01100", |
cp0_cause when "01101", |
cp0_epc & "00" when others; |
|
1058,7 → 1109,6
-- Implementation notes |
-------------------------------------------------------------------------------- |
-- @note1 : |
-- |
-- This is the meaning of these two signals: |
-- pipeline_stalled & stalled_interlock => |
-- "00" => normal state |
1076,4 → 1126,11
-- @note2: |
-- The logic that checks register indices for data hazards is 'commented out' |
-- because it has not been tested yet. |
-- |
-- @note3: |
-- CP0 instructions (mtc0, mfc0 and rfe) are only partially decoded. |
-- This is possible because no other VALID MIPS* opcode shares the decoded |
-- part; that is, we're not going to misdecode a MIPS32 opcode, but we MIGHT |
-- mistake a bad opcode for a COP0; we'll live with that for the time being. |
-- |
-------------------------------------------------------------------------------- |