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////////////////////////////////////////////////////////////////// // // // Decode stage of Amber 2 Core // // // // This file is part of the Amber project // // http://www.opencores.org/project,amber // // // // Description // // This module is the most complex part of the Amber core // // It decodes and sequences all instructions and handles all // // interrupts // // // // Author(s): // // - Conor Santifort, csantifort.amber@gmail.com // // // ////////////////////////////////////////////////////////////////// // // // Copyright (C) 2010 Authors and OPENCORES.ORG // // // // This source file may be used and distributed without // // restriction provided that this copyright statement is not // // removed from the file and that any derivative work contains // // the original copyright notice and the associated disclaimer. // // // // This source file is free software; you can redistribute it // // and/or modify it under the terms of the GNU Lesser General // // Public License as published by the Free Software Foundation; // // either version 2.1 of the License, or (at your option) any // // later version. // // // // This source 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 Lesser General Public License for more // // details. // // // // You should have received a copy of the GNU Lesser General // // Public License along with this source; if not, download it // // from http://www.opencores.org/lgpl.shtml // // // ////////////////////////////////////////////////////////////////// `include "global_defines.vh" module a23_decode ( input i_clk, input [31:0] i_read_data, input i_fetch_stall, // stall all stages of the cpu at the same time input i_irq, // interrupt request input i_firq, // Fast interrupt request input i_dabt, // data abort interrupt request input i_iabt, // instruction pre-fetch abort flag input i_adex, // Address Exception input [31:0] i_execute_address, // Registered address output by execute stage // 2 LSBs of read address used for calculating // shift in LDRB ops input [7:0] i_abt_status, // Abort status input [31:0] i_execute_status_bits, // current status bits values in execute stage input i_multiply_done, // multiply unit is nearly done // -------------------------------------------------- // Control signals to execute stage // -------------------------------------------------- output reg [31:0] o_read_data = 1'd0, output reg [4:0] o_read_data_alignment = 1'd0, // 2 LSBs of read address used for calculating shift in LDRB ops output reg [31:0] o_imm32 = 'd0, output reg [4:0] o_imm_shift_amount = 'd0, output reg o_shift_imm_zero = 'd0, output wire [3:0] o_condition, output reg o_exclusive_exec = 'd0, // exclusive access request ( swap instruction ) output reg o_data_access_exec = 'd0, // high means the memory access is a read // read or write, low for instruction output wire [1:0] o_status_bits_mode, output wire o_status_bits_irq_mask, output wire o_status_bits_firq_mask, output reg [3:0] o_rm_sel = 'd0, output reg [3:0] o_rds_sel = 'd0, output reg [3:0] o_rn_sel = 'd0, output [3:0] o_rm_sel_nxt, output [3:0] o_rds_sel_nxt, output [3:0] o_rn_sel_nxt, output reg [1:0] o_barrel_shift_amount_sel = 'd0, output reg [1:0] o_barrel_shift_data_sel = 'd0, output reg [1:0] o_barrel_shift_function = 'd0, output reg [8:0] o_alu_function = 'd0, output reg o_use_carry_in = 'd0, output reg [1:0] o_multiply_function = 'd0, output reg [2:0] o_interrupt_vector_sel = 'd0, output wire [3:0] o_address_sel, output wire [1:0] o_pc_sel, output reg [1:0] o_byte_enable_sel = 'd0, // byte, halfword or word write output reg [2:0] o_status_bits_sel = 'd0, output reg [2:0] o_reg_write_sel, output reg o_user_mode_regs_load, output reg o_user_mode_regs_store_nxt, output reg o_firq_not_user_mode, output reg o_write_data_wen = 'd0, output reg o_base_address_wen = 'd0, // save LDM base address register // in case of data abort output wire o_pc_wen, output reg [14:0] o_reg_bank_wen = 'd0, output reg [3:0] o_reg_bank_wsel = 'd0, output reg o_status_bits_flags_wen = 'd0, output reg o_status_bits_mode_wen = 'd0, output reg o_status_bits_irq_mask_wen = 'd0, output reg o_status_bits_firq_mask_wen = 'd0, // -------------------------------------------------- // Co-Processor interface // -------------------------------------------------- output reg [2:0] o_copro_opcode1 = 'd0, output reg [2:0] o_copro_opcode2 = 'd0, output reg [3:0] o_copro_crn = 'd0, output reg [3:0] o_copro_crm = 'd0, output reg [3:0] o_copro_num = 'd0, output reg [1:0] o_copro_operation = 'd0, // 0 = no operation, // 1 = Move to Amber Core Register from Coprocessor // 2 = Move to Coprocessor from Amber Core Register output reg o_copro_write_data_wen = 'd0, output o_iabt_trigger, output [31:0] o_iabt_address, output [7:0] o_iabt_status, output o_dabt_trigger, output [31:0] o_dabt_address, output [7:0] o_dabt_status ); `include "a23_localparams.vh" `include "a23_functions.vh" localparam [4:0] RST_WAIT1 = 5'd0, RST_WAIT2 = 5'd1, INT_WAIT1 = 5'd2, INT_WAIT2 = 5'd3, EXECUTE = 5'd4, PRE_FETCH_EXEC = 5'd5, // Execute the Pre-Fetched Instruction MEM_WAIT1 = 5'd6, // conditionally decode current instruction, in case // previous instruction does not execute in S2 MEM_WAIT2 = 5'd7, PC_STALL1 = 5'd8, // Program Counter altered // conditionally decude current instruction, in case // previous instruction does not execute in S2 PC_STALL2 = 5'd9, MTRANS_EXEC1 = 5'd10, MTRANS_EXEC2 = 5'd11, MTRANS_EXEC3 = 5'd12, MTRANS_EXEC3B = 5'd13, MTRANS_EXEC4 = 5'd14, MTRANS5_ABORT = 5'd15, MULT_PROC1 = 5'd16, // first cycle, save pre fetch instruction MULT_PROC2 = 5'd17, // do multiplication MULT_STORE = 5'd19, // save RdLo MULT_ACCUMU = 5'd20, // Accumulate add lower 32 bits SWAP_WRITE = 5'd22, SWAP_WAIT1 = 5'd23, SWAP_WAIT2 = 5'd24, COPRO_WAIT = 5'd25; // ======================================================== // Internal signals // ======================================================== wire [31:0] instruction; wire instruction_iabt; // abort flag, follows the instruction wire instruction_adex; // address exception flag, follows the instruction wire [31:0] instruction_address; // instruction virtual address, follows // the instruction wire [7:0] instruction_iabt_status; // abort status, follows the instruction wire [1:0] instruction_sel; reg [3:0] itype; wire [3:0] opcode; wire [7:0] imm8; wire [31:0] offset12; wire [31:0] offset24; wire [4:0] shift_imm; wire opcode_compare; wire mem_op; wire load_op; wire store_op; wire write_pc; wire immediate_shifter_operand; wire rds_use_rs; wire branch; wire mem_op_pre_indexed; wire mem_op_post_indexed; // Flop inputs wire [31:0] imm32_nxt; wire [4:0] imm_shift_amount_nxt; wire shift_imm_zero_nxt; wire [3:0] condition_nxt; reg exclusive_exec_nxt; reg data_access_exec_nxt; wire shift_extend; reg [1:0] barrel_shift_function_nxt; wire [8:0] alu_function_nxt; reg use_carry_in_nxt; reg [1:0] multiply_function_nxt; reg [1:0] status_bits_mode_nxt; reg status_bits_irq_mask_nxt; reg status_bits_firq_mask_nxt; reg [1:0] barrel_shift_amount_sel_nxt; reg [1:0] barrel_shift_data_sel_nxt; reg [3:0] address_sel_nxt; reg [1:0] pc_sel_nxt; reg [1:0] byte_enable_sel_nxt; reg [2:0] status_bits_sel_nxt; reg [2:0] reg_write_sel_nxt; reg user_mode_regs_load_nxt; wire firq_not_user_mode_nxt; // ALU Function signals reg alu_swap_sel_nxt; reg alu_not_sel_nxt; reg [1:0] alu_cin_sel_nxt; reg alu_cout_sel_nxt; reg [3:0] alu_out_sel_nxt; reg write_data_wen_nxt; reg copro_write_data_wen_nxt; reg base_address_wen_nxt; reg pc_wen_nxt; reg [3:0] reg_bank_wsel_nxt; reg status_bits_flags_wen_nxt; reg status_bits_mode_wen_nxt; reg status_bits_irq_mask_wen_nxt; reg status_bits_firq_mask_wen_nxt; reg saved_current_instruction_wen; // saved load instruction reg pre_fetch_instruction_wen; // pre-fetch instruction reg [4:0] control_state = RST_WAIT1; reg [4:0] control_state_nxt; wire dabt; reg dabt_reg = 'd0; reg dabt_reg_d1; reg iabt_reg = 'd0; reg adex_reg = 'd0; reg [31:0] abt_address_reg = 'd0; reg [7:0] abt_status_reg = 'd0; reg [31:0] saved_current_instruction = 'd0; reg saved_current_instruction_iabt = 'd0; // access abort flag reg saved_current_instruction_adex = 'd0; // address exception reg [31:0] saved_current_instruction_address = 'd0; // virtual address of abort instruction reg [7:0] saved_current_instruction_iabt_status = 'd0; // status of abort instruction reg [31:0] pre_fetch_instruction = 'd0; reg pre_fetch_instruction_iabt = 'd0; // access abort flag reg pre_fetch_instruction_adex = 'd0; // address exception reg [31:0] pre_fetch_instruction_address = 'd0; // virtual address of abort instruction reg [7:0] pre_fetch_instruction_iabt_status = 'd0; // status of abort instruction wire instruction_valid; wire instruction_execute; reg [3:0] mtrans_reg; // the current register being accessed as part of STM/LDM reg [3:0] mtrans_reg_d1 = 'd0; // delayed by 1 period reg [3:0] mtrans_reg_d2 = 'd0; // delayed by 2 periods reg [31:0] mtrans_instruction_nxt; wire [31:0] mtrans_base_reg_change; wire [4:0] mtrans_num_registers; wire use_saved_current_instruction; wire use_pre_fetch_instruction; wire interrupt; wire [1:0] interrupt_mode; wire [2:0] next_interrupt; reg irq = 'd0; reg firq = 'd0; wire firq_request; wire irq_request; wire swi_request; wire und_request; wire dabt_request; reg [1:0] copro_operation_nxt; reg mtrans_r15 = 'd0; reg mtrans_r15_nxt; reg restore_base_address = 'd0; reg restore_base_address_nxt; wire regop_set_flags; // ======================================================== // registers for output ports with non-zero initial values // ======================================================== reg [3:0] condition_r = 4'he; // 4'he = al reg [1:0] status_bits_mode_r = 2'b11; // SVC reg status_bits_irq_mask_r = 1'd1; reg status_bits_firq_mask_r = 1'd1; reg [3:0] address_sel_r = 4'd2; reg [1:0] pc_sel_r = 2'd2; reg pc_wen_r = 1'd1; assign o_condition = condition_r; assign o_status_bits_mode = status_bits_mode_r; assign o_status_bits_irq_mask = status_bits_irq_mask_r; assign o_status_bits_firq_mask = status_bits_firq_mask_r; assign o_address_sel = address_sel_r; assign o_pc_sel = pc_sel_r; assign o_pc_wen = pc_wen_r; // ======================================================== // Instruction Abort and Data Abort outputs // ======================================================== assign o_iabt_trigger = instruction_iabt && status_bits_mode_r == SVC && control_state == INT_WAIT1; assign o_iabt_address = instruction_address; assign o_iabt_status = instruction_iabt_status; assign o_dabt_trigger = dabt_reg && !dabt_reg_d1; assign o_dabt_address = abt_address_reg; assign o_dabt_status = abt_status_reg; // ======================================================== // Instruction Decode // ======================================================== // for instructions that take more than one cycle // the instruction is saved in the 'saved_mem_instruction' // register and then that register is used for the rest of // the execution of the instruction. // But if the instruction does not execute because of the // condition, then need to select the next instruction to // decode assign use_saved_current_instruction = instruction_execute && ( control_state == MEM_WAIT1 || control_state == MEM_WAIT2 || control_state == MTRANS_EXEC1 || control_state == MTRANS_EXEC2 || control_state == MTRANS_EXEC3 || control_state == MTRANS_EXEC3B || control_state == MTRANS_EXEC4 || control_state == MTRANS5_ABORT || control_state == MULT_PROC1 || control_state == MULT_PROC2 || control_state == MULT_ACCUMU || control_state == MULT_STORE || control_state == INT_WAIT1 || control_state == INT_WAIT2 || control_state == SWAP_WRITE || control_state == SWAP_WAIT1 || control_state == SWAP_WAIT2 || control_state == COPRO_WAIT ); assign use_pre_fetch_instruction = control_state == PRE_FETCH_EXEC; assign instruction_sel = use_saved_current_instruction ? 2'd1 : // saved_current_instruction use_pre_fetch_instruction ? 2'd2 : // pre_fetch_instruction 2'd0 ; // o_read_data assign instruction = instruction_sel == 2'd0 ? o_read_data : instruction_sel == 2'd1 ? saved_current_instruction : pre_fetch_instruction ; // abort flag assign instruction_iabt = instruction_sel == 2'd0 ? iabt_reg : instruction_sel == 2'd1 ? saved_current_instruction_iabt : pre_fetch_instruction_iabt ; assign instruction_address = instruction_sel == 2'd0 ? abt_address_reg : instruction_sel == 2'd1 ? saved_current_instruction_address : pre_fetch_instruction_address ; assign instruction_iabt_status = instruction_sel == 2'd0 ? abt_status_reg : instruction_sel == 2'd1 ? saved_current_instruction_iabt_status : pre_fetch_instruction_iabt_status ; // instruction address exception assign instruction_adex = instruction_sel == 2'd0 ? adex_reg : instruction_sel == 2'd1 ? saved_current_instruction_adex : pre_fetch_instruction_adex ; // Instruction Decode - Order is important! always @* casez ({instruction[27:20], instruction[7:4]}) 12'b00010?001001 : itype = SWAP; 12'b000000??1001 : itype = MULT; 12'b00?????????? : itype = REGOP; 12'b01?????????? : itype = TRANS; 12'b100????????? : itype = MTRANS; 12'b101????????? : itype = BRANCH; 12'b110????????? : itype = CODTRANS; 12'b1110???????0 : itype = COREGOP; 12'b1110???????1 : itype = CORTRANS; default: itype = SWI; endcase // ======================================================== // Fixed fields within the instruction // ======================================================== assign opcode = instruction[24:21]; assign condition_nxt = instruction[31:28]; assign o_rm_sel_nxt = instruction[3:0]; assign o_rn_sel_nxt = branch ? 4'd15 : // Use PC to calculate branch destination instruction[19:16] ; assign o_rds_sel_nxt = control_state == SWAP_WRITE ? instruction[3:0] : // Rm gets written out to memory itype == MTRANS ? mtrans_reg : branch ? 4'd15 : // Update the PC rds_use_rs ? instruction[11:8] : instruction[15:12] ; assign shift_imm = instruction[11:7]; // this is used for RRX assign shift_extend = !instruction[25] && !instruction[4] && !(|instruction[11:7]) && instruction[6:5] == 2'b11; assign offset12 = { 20'h0, instruction[11:0]}; assign offset24 = {{6{instruction[23]}}, instruction[23:0], 2'd0 }; // sign extend assign imm8 = instruction[7:0]; assign immediate_shifter_operand = instruction[25]; assign rds_use_rs = (itype == REGOP && !instruction[25] && instruction[4]) || (itype == MULT && (control_state == MULT_PROC1 || control_state == MULT_PROC2 || instruction_valid && !interrupt )) ; assign branch = itype == BRANCH; assign opcode_compare = opcode == CMP || opcode == CMN || opcode == TEQ || opcode == TST ; assign mem_op = itype == TRANS; assign load_op = mem_op && instruction[20]; assign store_op = mem_op && !instruction[20]; assign write_pc = pc_wen_nxt && pc_sel_nxt != 2'd0; assign regop_set_flags = itype == REGOP && instruction[20]; assign mem_op_pre_indexed = instruction[24] && instruction[21]; assign mem_op_post_indexed = !instruction[24]; assign imm32_nxt = // add 0 to Rm itype == MULT ? { 32'd0 } : // 4 x number of registers itype == MTRANS ? { mtrans_base_reg_change } : itype == BRANCH ? { offset24 } : itype == TRANS ? { offset12 } : instruction[11:8] == 4'h0 ? { 24'h0, imm8[7:0] } : instruction[11:8] == 4'h1 ? { imm8[1:0], 24'h0, imm8[7:2] } : instruction[11:8] == 4'h2 ? { imm8[3:0], 24'h0, imm8[7:4] } : instruction[11:8] == 4'h3 ? { imm8[5:0], 24'h0, imm8[7:6] } : instruction[11:8] == 4'h4 ? { imm8[7:0], 24'h0 } : instruction[11:8] == 4'h5 ? { 2'h0, imm8[7:0], 22'h0 } : instruction[11:8] == 4'h6 ? { 4'h0, imm8[7:0], 20'h0 } : instruction[11:8] == 4'h7 ? { 6'h0, imm8[7:0], 18'h0 } : instruction[11:8] == 4'h8 ? { 8'h0, imm8[7:0], 16'h0 } : instruction[11:8] == 4'h9 ? { 10'h0, imm8[7:0], 14'h0 } : instruction[11:8] == 4'ha ? { 12'h0, imm8[7:0], 12'h0 } : instruction[11:8] == 4'hb ? { 14'h0, imm8[7:0], 10'h0 } : instruction[11:8] == 4'hc ? { 16'h0, imm8[7:0], 8'h0 } : instruction[11:8] == 4'hd ? { 18'h0, imm8[7:0], 6'h0 } : instruction[11:8] == 4'he ? { 20'h0, imm8[7:0], 4'h0 } : { 22'h0, imm8[7:0], 2'h0 } ; assign imm_shift_amount_nxt = shift_imm ; // This signal is encoded in the decode stage because // it is on the critical path in the execute stage assign shift_imm_zero_nxt = imm_shift_amount_nxt == 5'd0 && // immediate amount = 0 barrel_shift_amount_sel_nxt == 2'd2; // shift immediate amount assign alu_function_nxt = { alu_swap_sel_nxt, alu_not_sel_nxt, alu_cin_sel_nxt, alu_cout_sel_nxt, alu_out_sel_nxt }; // ======================================================== // MTRANS Operations // ======================================================== // Bit 15 = r15 // Bit 0 = R0 // In LDM and STM instructions R0 is loaded or stored first always @* casez (instruction[15:0]) 16'b???????????????1 : mtrans_reg = 4'h0 ; 16'b??????????????10 : mtrans_reg = 4'h1 ; 16'b?????????????100 : mtrans_reg = 4'h2 ; 16'b????????????1000 : mtrans_reg = 4'h3 ; 16'b???????????10000 : mtrans_reg = 4'h4 ; 16'b??????????100000 : mtrans_reg = 4'h5 ; 16'b?????????1000000 : mtrans_reg = 4'h6 ; 16'b????????10000000 : mtrans_reg = 4'h7 ; 16'b???????100000000 : mtrans_reg = 4'h8 ; 16'b??????1000000000 : mtrans_reg = 4'h9 ; 16'b?????10000000000 : mtrans_reg = 4'ha ; 16'b????100000000000 : mtrans_reg = 4'hb ; 16'b???1000000000000 : mtrans_reg = 4'hc ; 16'b??10000000000000 : mtrans_reg = 4'hd ; 16'b?100000000000000 : mtrans_reg = 4'he ; default : mtrans_reg = 4'hf ; endcase always @* casez (instruction[15:0]) 16'b???????????????1 : mtrans_instruction_nxt = {instruction[31:16], instruction[15: 1], 1'd0}; 16'b??????????????10 : mtrans_instruction_nxt = {instruction[31:16], instruction[15: 2], 2'd0}; 16'b?????????????100 : mtrans_instruction_nxt = {instruction[31:16], instruction[15: 3], 3'd0}; 16'b????????????1000 : mtrans_instruction_nxt = {instruction[31:16], instruction[15: 4], 4'd0}; 16'b???????????10000 : mtrans_instruction_nxt = {instruction[31:16], instruction[15: 5], 5'd0}; 16'b??????????100000 : mtrans_instruction_nxt = {instruction[31:16], instruction[15: 6], 6'd0}; 16'b?????????1000000 : mtrans_instruction_nxt = {instruction[31:16], instruction[15: 7], 7'd0}; 16'b????????10000000 : mtrans_instruction_nxt = {instruction[31:16], instruction[15: 8], 8'd0}; 16'b???????100000000 : mtrans_instruction_nxt = {instruction[31:16], instruction[15: 9], 9'd0}; 16'b??????1000000000 : mtrans_instruction_nxt = {instruction[31:16], instruction[15:10], 10'd0}; 16'b?????10000000000 : mtrans_instruction_nxt = {instruction[31:16], instruction[15:11], 11'd0}; 16'b????100000000000 : mtrans_instruction_nxt = {instruction[31:16], instruction[15:12], 12'd0}; 16'b???1000000000000 : mtrans_instruction_nxt = {instruction[31:16], instruction[15:13], 13'd0}; 16'b??10000000000000 : mtrans_instruction_nxt = {instruction[31:16], instruction[15:14], 14'd0}; 16'b?100000000000000 : mtrans_instruction_nxt = {instruction[31:16], instruction[15 ], 15'd0}; default : mtrans_instruction_nxt = {instruction[31:16], 16'd0}; endcase // number of registers to be stored assign mtrans_num_registers = {4'd0, instruction[15]} + {4'd0, instruction[14]} + {4'd0, instruction[13]} + {4'd0, instruction[12]} + {4'd0, instruction[11]} + {4'd0, instruction[10]} + {4'd0, instruction[ 9]} + {4'd0, instruction[ 8]} + {4'd0, instruction[ 7]} + {4'd0, instruction[ 6]} + {4'd0, instruction[ 5]} + {4'd0, instruction[ 4]} + {4'd0, instruction[ 3]} + {4'd0, instruction[ 2]} + {4'd0, instruction[ 1]} + {4'd0, instruction[ 0]} ; // 4 x number of registers to be stored assign mtrans_base_reg_change = {25'd0, mtrans_num_registers, 2'd0}; // ======================================================== // Interrupts // ======================================================== assign firq_request = firq && !i_execute_status_bits[26]; assign irq_request = irq && !i_execute_status_bits[27]; assign swi_request = itype == SWI; assign dabt_request = dabt_reg; // copro15 and copro13 only supports reg trans opcodes // all other opcodes involving co-processors cause an // undefined instrution interrupt assign und_request = itype == CODTRANS || itype == COREGOP || ( itype == CORTRANS && instruction[11:8] != 4'd15 ); // in order of priority !! // Highest // 1 Reset // 2 Data Abort (including data TLB miss) // 3 FIRQ // 4 IRQ // 5 Prefetch Abort (including prefetch TLB miss) // 6 Undefined instruction, SWI // Lowest assign next_interrupt = dabt_request ? 3'd1 : // Data Abort firq_request ? 3'd2 : // FIRQ irq_request ? 3'd3 : // IRQ instruction_adex ? 3'd4 : // Address Exception instruction_iabt ? 3'd5 : // PreFetch Abort, only triggered // if the instruction is used und_request ? 3'd6 : // Undefined Instruction swi_request ? 3'd7 : // SWI 3'd0 ; // none // SWI and undefined instructions do not cause an interrupt in the decode // stage. They only trigger interrupts if they arfe executed, so the // interrupt is triggered if the execute condition is met in the execute stage assign interrupt = next_interrupt != 3'd0 && next_interrupt != 3'd7 && // SWI next_interrupt != 3'd6 ; // undefined interrupt assign interrupt_mode = next_interrupt == 3'd2 ? FIRQ : next_interrupt == 3'd3 ? IRQ : next_interrupt == 3'd4 ? SVC : next_interrupt == 3'd5 ? SVC : next_interrupt == 3'd6 ? SVC : next_interrupt == 3'd7 ? SVC : next_interrupt == 3'd1 ? SVC : USR ; // ======================================================== // Generate control signals // ======================================================== always @* begin // default mode status_bits_mode_nxt = i_execute_status_bits[1:0]; // change to mode in execute stage get reflected // back to this stage automatically status_bits_irq_mask_nxt = status_bits_irq_mask_r; status_bits_firq_mask_nxt = status_bits_firq_mask_r; exclusive_exec_nxt = 1'd0; data_access_exec_nxt = 1'd0; copro_operation_nxt = 'd0; // Save an instruction to use later saved_current_instruction_wen = 1'd0; pre_fetch_instruction_wen = 1'd0; mtrans_r15_nxt = mtrans_r15; restore_base_address_nxt = restore_base_address; // default Mux Select values barrel_shift_amount_sel_nxt = 'd0; // don't shift the input barrel_shift_data_sel_nxt = 'd0; // immediate value barrel_shift_function_nxt = 'd0; use_carry_in_nxt = 'd0; multiply_function_nxt = 'd0; address_sel_nxt = 'd0; pc_sel_nxt = 'd0; byte_enable_sel_nxt = 'd0; status_bits_sel_nxt = 'd0; reg_write_sel_nxt = 'd0; user_mode_regs_load_nxt = 'd0; o_user_mode_regs_store_nxt = 'd0; // ALU Muxes alu_swap_sel_nxt = 'd0; alu_not_sel_nxt = 'd0; alu_cin_sel_nxt = 'd0; alu_cout_sel_nxt = 'd0; alu_out_sel_nxt = 'd0; // default Flop Write Enable values write_data_wen_nxt = 'd0; copro_write_data_wen_nxt = 'd0; base_address_wen_nxt = 'd0; pc_wen_nxt = 'd1; reg_bank_wsel_nxt = 'hF; // Don't select any status_bits_flags_wen_nxt = 'd0; status_bits_mode_wen_nxt = 'd0; status_bits_irq_mask_wen_nxt = 'd0; status_bits_firq_mask_wen_nxt = 'd0; if ( instruction_valid && !interrupt ) begin if ( itype == REGOP ) begin if ( !opcode_compare ) begin // Check is the load destination is the PC if (instruction[15:12] == 4'd15) begin pc_sel_nxt = 2'd1; // alu_out address_sel_nxt = 4'd1; // alu_out end else reg_bank_wsel_nxt = instruction[15:12]; end if ( !immediate_shifter_operand ) barrel_shift_function_nxt = instruction[6:5]; if ( !immediate_shifter_operand ) barrel_shift_data_sel_nxt = 2'd2; // Shift value from Rm register if ( !immediate_shifter_operand && instruction[4] ) barrel_shift_amount_sel_nxt = 2'd1; // Shift amount from Rs registter if ( !immediate_shifter_operand && !instruction[4] ) barrel_shift_amount_sel_nxt = 2'd2; // Shift immediate amount // regops that do not change the overflow flag if ( opcode == AND || opcode == EOR || opcode == TST || opcode == TEQ || opcode == ORR || opcode == MOV || opcode == BIC || opcode == MVN ) status_bits_sel_nxt = 3'd5; if ( opcode == ADD || opcode == CMN ) // CMN is just like an ADD begin alu_out_sel_nxt = 4'd1; // Add use_carry_in_nxt = shift_extend; end if ( opcode == ADC ) // Add with Carry begin alu_out_sel_nxt = 4'd1; // Add alu_cin_sel_nxt = 2'd2; // carry in from status_bits use_carry_in_nxt = shift_extend; end if ( opcode == SUB || opcode == CMP ) // Subtract begin alu_out_sel_nxt = 4'd1; // Add alu_cin_sel_nxt = 2'd1; // cin = 1 alu_not_sel_nxt = 1'd1; // invert B end // SBC (Subtract with Carry) subtracts the value of its // second operand and the value of NOT(Carry flag) from // the value of its first operand. // Rd = Rn - shifter_operand - NOT(C Flag) if ( opcode == SBC ) // Subtract with Carry begin alu_out_sel_nxt = 4'd1; // Add alu_cin_sel_nxt = 2'd2; // carry in from status_bits alu_not_sel_nxt = 1'd1; // invert B use_carry_in_nxt = 1'd1; end if ( opcode == RSB ) // Reverse Subtract begin alu_out_sel_nxt = 4'd1; // Add alu_cin_sel_nxt = 2'd1; // cin = 1 alu_not_sel_nxt = 1'd1; // invert B alu_swap_sel_nxt = 1'd1; // swap A and B end if ( opcode == RSC ) // Reverse Subtract with carry begin alu_out_sel_nxt = 4'd1; // Add alu_cin_sel_nxt = 2'd2; // carry in from status_bits alu_not_sel_nxt = 1'd1; // invert B alu_swap_sel_nxt = 1'd1; // swap A and B use_carry_in_nxt = 1'd1; end if ( opcode == AND || opcode == TST ) // Logical AND, Test (using AND operator) begin alu_out_sel_nxt = 4'd8; // AND alu_cout_sel_nxt = 1'd1; // i_barrel_shift_carry end if ( opcode == EOR || opcode == TEQ ) // Logical Exclusive OR, Test Equivalence (using EOR operator) begin alu_out_sel_nxt = 4'd6; // XOR alu_cout_sel_nxt = 1'd1; // i_barrel_shift_carry use_carry_in_nxt = 1'd1; end if ( opcode == ORR ) begin alu_out_sel_nxt = 4'd7; // OR alu_cout_sel_nxt = 1'd1; // i_barrel_shift_carry use_carry_in_nxt = 1'd1; end if ( opcode == BIC ) // Bit Clear (using AND & NOT operators) begin alu_out_sel_nxt = 4'd8; // AND alu_not_sel_nxt = 1'd1; // invert B alu_cout_sel_nxt = 1'd1; // i_barrel_shift_carry use_carry_in_nxt = 1'd1; end if ( opcode == MOV ) // Move begin alu_cout_sel_nxt = 1'd1; // i_barrel_shift_carry use_carry_in_nxt = 1'd1; end if ( opcode == MVN ) // Move NOT begin alu_not_sel_nxt = 1'd1; // invert B alu_cout_sel_nxt = 1'd1; // i_barrel_shift_carry use_carry_in_nxt = 1'd1; end end // Load & Store instructions if ( mem_op ) begin saved_current_instruction_wen = 1'd1; // Save the memory access instruction to refer back to later pc_wen_nxt = 1'd0; // hold current PC value data_access_exec_nxt = 1'd1; // indicate that its a data read or write, // rather than an instruction fetch alu_out_sel_nxt = 4'd1; // Add if ( !instruction[23] ) // U: Subtract offset begin alu_cin_sel_nxt = 2'd1; // cin = 1 alu_not_sel_nxt = 1'd1; // invert B end if ( store_op ) begin write_data_wen_nxt = 1'd1; if ( itype == TRANS && instruction[22] ) byte_enable_sel_nxt = 2'd1; // Save byte end // need to update the register holding the address ? // This is Rn bits [19:16] if ( mem_op_pre_indexed || mem_op_post_indexed ) begin // Check is the load destination is the PC if ( o_rn_sel_nxt == 4'd15 ) pc_sel_nxt = 2'd1; else reg_bank_wsel_nxt = o_rn_sel_nxt; end // if post-indexed, then use Rn rather than ALU output, as address if ( mem_op_post_indexed ) address_sel_nxt = 4'd4; // Rn else address_sel_nxt = 4'd1; // alu out if ( instruction[25] && itype == TRANS ) barrel_shift_data_sel_nxt = 2'd2; // Shift value from Rm register if ( itype == TRANS && instruction[25] && shift_imm != 5'd0 ) begin barrel_shift_function_nxt = instruction[6:5]; barrel_shift_amount_sel_nxt = 2'd2; // imm_shift_amount end end if ( itype == BRANCH ) begin pc_sel_nxt = 2'd1; // alu_out address_sel_nxt = 4'd1; // alu_out alu_out_sel_nxt = 4'd1; // Add if ( instruction[24] ) // Link begin reg_bank_wsel_nxt = 4'd14; // Save PC to LR reg_write_sel_nxt = 3'd1; // pc - 32'd4 end end if ( itype == MTRANS ) begin saved_current_instruction_wen = 1'd1; // Save the memory access instruction to refer back to later pc_wen_nxt = 1'd0; // hold current PC value data_access_exec_nxt = 1'd1; // indicate that its a data read or write, // rather than an instruction fetch alu_out_sel_nxt = 4'd1; // Add mtrans_r15_nxt = instruction[15]; // load or save r15 ? base_address_wen_nxt = 1'd1; // Save the value of the register used for the base address, // in case of a data abort, and need to restore the value // The spec says - // If the instruction would have overwritten the base with data // (that is, it has the base in the transfer list), the overwriting is prevented. // This is true even when the abort occurs after the base word gets loaded restore_base_address_nxt = instruction[20] && (instruction[15:0] & (1'd1 << instruction[19:16])); // Increment or Decrement if ( instruction[23] ) // increment begin if ( instruction[24] ) // increment before address_sel_nxt = 4'd7; // Rn + 4 else address_sel_nxt = 4'd4; // Rn end else // decrement begin alu_cin_sel_nxt = 2'd1; // cin = 1 alu_not_sel_nxt = 1'd1; // invert B if ( !instruction[24] ) // decrement after address_sel_nxt = 4'd6; // alu out + 4 else address_sel_nxt = 4'd1; // alu out end // Load or store ? if ( !instruction[20] ) // Store write_data_wen_nxt = 1'd1; // LDM: load into user mode registers, when in priviledged mode // Don't use mtrans_r15 here because its not loaded yet //if ( {instruction[22],instruction[20],instruction[15]} == 3'b110 ) if ( {instruction[22:20],instruction[15]} == 4'b1010 ) user_mode_regs_load_nxt = 1'd1; // SDM: store the user mode registers, when in priviledged mode //if ( {instruction[22],instruction[20]} == 3'b10 ) if ( {instruction[22:20]} == 3'b100 ) o_user_mode_regs_store_nxt = 1'd1; // update the base register ? if ( instruction[21] ) // the W bit reg_bank_wsel_nxt = o_rn_sel_nxt; end if ( itype == MULT ) begin multiply_function_nxt[0] = 1'd1; // set enable // some bits can be changed just below saved_current_instruction_wen = 1'd1; // Save the Multiply instruction to // refer back to later pc_wen_nxt = 1'd0; // hold current PC value if ( instruction[21] ) multiply_function_nxt[1] = 1'd1; // accumulate end // swp - do read part first if ( itype == SWAP ) begin saved_current_instruction_wen = 1'd1; // Save the memory access instruction to refer back to later pc_wen_nxt = 1'd0; // hold current PC value data_access_exec_nxt = 1'd1; // indicate that its a data read or write, // rather than an instruction fetch barrel_shift_data_sel_nxt = 2'd2; // Shift value from Rm register address_sel_nxt = 4'd4; // Rn exclusive_exec_nxt = 1'd1; // signal an exclusive access end // mcr & mrc - takes two cycles if ( itype == CORTRANS && !und_request ) begin saved_current_instruction_wen = 1'd1; // Save the memory access instruction to refer back to later pc_wen_nxt = 1'd0; // hold current PC value address_sel_nxt = 4'd3; // pc (not pc + 4) if ( instruction[20] ) // MRC copro_operation_nxt = 2'd1; // Register transfer from Co-Processor else // MCR begin // Don't enable operation to Co-Processor until next period // So it gets the Rd value from the execution stage at the same time copro_operation_nxt = 2'd0; copro_write_data_wen_nxt = 1'd1; // Rd register value to co-processor end end if ( itype == SWI || und_request ) begin // save address of next instruction to Supervisor Mode LR reg_write_sel_nxt = 3'd1; // pc -4 reg_bank_wsel_nxt = 4'd14; // LR address_sel_nxt = 4'd2; // interrupt_vector pc_sel_nxt = 2'd2; // interrupt_vector status_bits_mode_nxt = interrupt_mode; // e.g. Supervisor mode status_bits_mode_wen_nxt = 1'd1; // disable normal interrupts status_bits_irq_mask_nxt = 1'd1; status_bits_irq_mask_wen_nxt = 1'd1; end if ( regop_set_flags ) begin status_bits_flags_wen_nxt = 1'd1; // If <Rd> is r15, the ALU output is copied to the Status Bits. // Not allowed to use r15 for mul or lma instructions if ( instruction[15:12] == 4'd15 ) begin status_bits_sel_nxt = 3'd1; // alu out // Priviledged mode? Then also update the other status bits if ( i_execute_status_bits[1:0] != USR ) begin status_bits_mode_wen_nxt = 1'd1; status_bits_irq_mask_wen_nxt = 1'd1; status_bits_firq_mask_wen_nxt = 1'd1; end end end end // Handle asynchronous interrupts. // interrupts are processed only during execution states // multicycle instructions must complete before the interrupt starts // SWI, Address Exception and Undefined Instruction interrupts are only executed if the // instruction that causes the interrupt is conditionally executed so // its not handled here if ( instruction_valid && interrupt && next_interrupt != 3'd6 ) begin // Save the interrupt causing instruction to refer back to later // This also saves the instruction abort vma and status, in the case of an // instruction abort interrupt saved_current_instruction_wen = 1'd1; // save address of next instruction to Supervisor Mode LR // Address Exception ? if ( next_interrupt == 3'd4 ) reg_write_sel_nxt = 3'd7; // pc else reg_write_sel_nxt = 3'd1; // pc -4 reg_bank_wsel_nxt = 4'd14; // LR address_sel_nxt = 4'd2; // interrupt_vector pc_sel_nxt = 2'd2; // interrupt_vector status_bits_mode_nxt = interrupt_mode; // e.g. Supervisor mode status_bits_mode_wen_nxt = 1'd1; // disable normal interrupts status_bits_irq_mask_nxt = 1'd1; status_bits_irq_mask_wen_nxt = 1'd1; // disable fast interrupts if ( next_interrupt == 3'd2 ) // FIRQ begin status_bits_firq_mask_nxt = 1'd1; status_bits_firq_mask_wen_nxt = 1'd1; end end // previous instruction was either ldr or sdr // if it is currently executing in the execute stage do the following if ( control_state == MEM_WAIT1 ) begin // Save the next instruction to execute later // Do this even if this instruction does not execute because of Condition pre_fetch_instruction_wen = 1'd1; if ( instruction_execute ) // conditional execution state begin address_sel_nxt = 4'd3; // pc (not pc + 4) pc_wen_nxt = 1'd0; // hold current PC value end end // completion of load operation if ( control_state == MEM_WAIT2 && load_op ) begin barrel_shift_data_sel_nxt = 2'd1; // load word from memory barrel_shift_amount_sel_nxt = 2'd3; // shift by address[1:0] x 8 // shift needed if ( i_execute_address[1:0] != 2'd0 ) barrel_shift_function_nxt = ROR; // load a byte if ( itype == TRANS && instruction[22] ) alu_out_sel_nxt = 4'd3; // zero_extend8 if ( !dabt ) // dont load data there is an abort on the data read begin // Check if the load destination is the PC if (instruction[15:12] == 4'd15) begin pc_sel_nxt = 2'd1; // alu_out address_sel_nxt = 4'd1; // alu_out end else reg_bank_wsel_nxt = instruction[15:12]; end end // second cycle of multiple load or store if ( control_state == MTRANS_EXEC1 ) begin // Save the next instruction to execute later // Do this even if this instruction does not execute because of Condition pre_fetch_instruction_wen = 1'd1; if ( instruction_execute ) // conditional execution state begin address_sel_nxt = 4'd5; // o_address pc_wen_nxt = 1'd0; // hold current PC value data_access_exec_nxt = 1'd1; // indicate that its a data read or write, // rather than an instruction fetch if ( !instruction[20] ) // Store write_data_wen_nxt = 1'd1; // LDM: load into user mode registers, when in priviledged mode //if ( {instruction[22],instruction[20],mtrans_r15} == 3'b110 ) if ( {instruction[22:20],mtrans_r15} == 4'b1010 ) user_mode_regs_load_nxt = 1'd1; // SDM: store the user mode registers, when in priviledged mode //if ( {instruction[22],instruction[20]} == 2'b10 ) if ( {instruction[22:20]} == 3'b100 ) o_user_mode_regs_store_nxt = 1'd1; end end // third cycle of multiple load or store if ( control_state == MTRANS_EXEC2 ) begin address_sel_nxt = 4'd5; // o_address pc_wen_nxt = 1'd0; // hold current PC value data_access_exec_nxt = 1'd1; // indicate that its a data read or write, // rather than an instruction fetch barrel_shift_data_sel_nxt = 2'd1; // load word from memory // Load or Store if ( instruction[20] ) // Load begin // Can never be loading the PC in this state, as the PC is always // the last register in the set to be loaded if ( !dabt ) reg_bank_wsel_nxt = mtrans_reg_d2; end else // Store write_data_wen_nxt = 1'd1; // LDM: load into user mode registers, when in priviledged mode if ( {instruction[22],instruction[20],mtrans_r15} == 3'b110 ) user_mode_regs_load_nxt = 1'd1; // SDM: store the user mode registers, when in priviledged mode if ( {instruction[22],instruction[20]} == 2'b10 ) o_user_mode_regs_store_nxt = 1'd1; end // second or fourth cycle of multiple load or store if ( control_state == MTRANS_EXEC3 && instruction_execute ) begin address_sel_nxt = 4'd3; // pc (not pc + 4) pc_wen_nxt = 1'd0; // hold current PC value barrel_shift_data_sel_nxt = 2'd1; // load word from memory // Can never be loading the PC in this state, as the PC is always // the last register in the set to be loaded if ( instruction[20] && !dabt ) // Load reg_bank_wsel_nxt = mtrans_reg_d2; // LDM: load into user mode registers, when in priviledged mode if ( {instruction[22],instruction[20],mtrans_r15} == 3'b110 ) user_mode_regs_load_nxt = 1'd1; // SDM: store the user mode registers, when in priviledged mode //if ( {instruction[22:20]} == 3'b100 ) if ( {instruction[22],instruction[20]} == 2'b10 ) o_user_mode_regs_store_nxt = 1'd1; end // state is used for LMD/STM of a single register if ( control_state == MTRANS_EXEC3B && instruction_execute ) begin // Save the next instruction to execute later // Do this even if this instruction does not execute because of Condition pre_fetch_instruction_wen = 1'd1; address_sel_nxt = 4'd3; // pc (not pc + 4) pc_wen_nxt = 1'd0; // hold current PC value // LDM: load into user mode registers, when in priviledged mode if ( {instruction[22],instruction[20],mtrans_r15} == 3'b110 ) user_mode_regs_load_nxt = 1'd1; // SDM: store the user mode registers, when in priviledged mode if ( {instruction[22],instruction[20]} == 2'b10 ) o_user_mode_regs_store_nxt = 1'd1; end if ( control_state == MTRANS_EXEC4 ) begin barrel_shift_data_sel_nxt = 2'd1; // load word from memory if ( instruction[20] ) // Load begin if (!dabt) // dont overwrite registers or status if theres a data abort begin if ( mtrans_reg_d2 == 4'd15 ) // load new value into PC begin address_sel_nxt = 4'd1; // alu_out - read instructions using new PC value pc_sel_nxt = 2'd1; // alu_out pc_wen_nxt = 1'd1; // write PC // ldm with S bit and pc: the Status bits are updated // Node this must be done only at the end // so the register set is the set in the mode before it // gets changed. if ( instruction[22] ) begin status_bits_sel_nxt = 3'd1; // alu out status_bits_flags_wen_nxt = 1'd1; // Can't change the mode or mask bits in User mode if ( i_execute_status_bits[1:0] != USR ) begin status_bits_mode_wen_nxt = 1'd1; status_bits_irq_mask_wen_nxt = 1'd1; status_bits_firq_mask_wen_nxt = 1'd1; end end end else begin reg_bank_wsel_nxt = mtrans_reg_d2; end end end // we have a data abort interrupt if ( dabt ) begin pc_wen_nxt = 1'd0; // hold current PC value end // LDM: load into user mode registers, when in priviledged mode if ( {instruction[22],instruction[20],mtrans_r15} == 3'b110 ) user_mode_regs_load_nxt = 1'd1; // SDM: store the user mode registers, when in priviledged mode if ( {instruction[22],instruction[20]} == 2'b10 ) o_user_mode_regs_store_nxt = 1'd1; end // state is for when a data abort interrupt is triggered during an LDM if ( control_state == MTRANS5_ABORT ) begin // Restore the Base Address, if the base register is included in the // list of registers being loaded if (restore_base_address) // LDM with base address in register list begin reg_write_sel_nxt = 3'd6; // write base_register reg_bank_wsel_nxt = instruction[19:16]; // to Rn end end // Multiply or Multiply-Accumulate if ( control_state == MULT_PROC1 && instruction_execute ) begin // Save the next instruction to execute later // Do this even if this instruction does not execute because of Condition pre_fetch_instruction_wen = 1'd1; pc_wen_nxt = 1'd0; // hold current PC value multiply_function_nxt = o_multiply_function; end // Multiply or Multiply-Accumulate // Do multiplication // Wait for done or accumulate signal if ( control_state == MULT_PROC2 ) begin // Save the next instruction to execute later // Do this even if this instruction does not execute because of Condition pc_wen_nxt = 1'd0; // hold current PC value address_sel_nxt = 4'd3; // pc (not pc + 4) multiply_function_nxt = o_multiply_function; end // Save RdLo // always last cycle of all multiply or multiply accumulate operations if ( control_state == MULT_STORE ) begin reg_write_sel_nxt = 3'd2; // multiply_out multiply_function_nxt = o_multiply_function; if ( itype == MULT ) // 32-bit reg_bank_wsel_nxt = instruction[19:16]; // Rd else // 64-bit / Long reg_bank_wsel_nxt = instruction[15:12]; // RdLo if ( instruction[20] ) // the 'S' bit begin status_bits_sel_nxt = 3'd4; // { multiply_flags, status_bits_flags[1:0] } status_bits_flags_wen_nxt = 1'd1; end end // Add lower 32 bits to multiplication product if ( control_state == MULT_ACCUMU ) begin multiply_function_nxt = o_multiply_function; pc_wen_nxt = 1'd0; // hold current PC value address_sel_nxt = 4'd3; // pc (not pc + 4) end // swp - do write request in 2nd cycle if ( control_state == SWAP_WRITE && instruction_execute ) begin barrel_shift_data_sel_nxt = 2'd2; // Shift value from Rm register address_sel_nxt = 4'd4; // Rn write_data_wen_nxt = 1'd1; data_access_exec_nxt = 1'd1; // indicate that its a data read or write, // rather than an instruction fetch if ( instruction[22] ) byte_enable_sel_nxt = 2'd1; // Save byte if ( instruction_execute ) // conditional execution state pc_wen_nxt = 1'd0; // hold current PC value // Save the next instruction to execute later // Do this even if this instruction does not execute because of Condition pre_fetch_instruction_wen = 1'd1; end // swp - receive read response in 3rd cycle if ( control_state == SWAP_WAIT1 ) begin barrel_shift_data_sel_nxt = 2'd1; // load word from memory barrel_shift_amount_sel_nxt = 2'd3; // shift by address[1:0] x 8 // shift needed if ( i_execute_address[1:0] != 2'd0 ) barrel_shift_function_nxt = ROR; if ( instruction_execute ) // conditional execution state begin address_sel_nxt = 4'd3; // pc (not pc + 4) pc_wen_nxt = 1'd0; // hold current PC value end // load a byte if ( instruction[22] ) alu_out_sel_nxt = 4'd3; // zero_extend8 if ( !dabt ) begin // Check is the load destination is the PC if ( instruction[15:12] == 4'd15 ) begin pc_sel_nxt = 2'd1; // alu_out address_sel_nxt = 4'd1; // alu_out end else reg_bank_wsel_nxt = instruction[15:12]; end end // 1 cycle delay for Co-Processor Register access if ( control_state == COPRO_WAIT && instruction_execute ) begin pre_fetch_instruction_wen = 1'd1; if ( instruction[20] ) // mrc instruction begin // Check is the load destination is the PC if ( instruction[15:12] == 4'd15 ) begin // If r15 is specified for <Rd>, the condition code flags are // updated instead of a general-purpose register. status_bits_sel_nxt = 3'd3; // i_copro_data status_bits_flags_wen_nxt = 1'd1; // Can't change these in USR mode if ( i_execute_status_bits[1:0] != USR ) begin status_bits_mode_wen_nxt = 1'd1; status_bits_irq_mask_wen_nxt = 1'd1; status_bits_firq_mask_wen_nxt = 1'd1; end end else reg_bank_wsel_nxt = instruction[15:12]; reg_write_sel_nxt = 3'd5; // i_copro_data end else // mcr instruction begin copro_operation_nxt = 2'd2; // Register transfer to Co-Processor end end // Have just changed the status_bits mode but this // creates a 1 cycle gap with the old mode // coming back from execute into instruction_decode // So squash that old mode value during this // cycle of the interrupt transition if ( control_state == INT_WAIT1 ) status_bits_mode_nxt = status_bits_mode_r; // Supervisor mode end // Speed up the long path from u_decode/o_read_data to u_register_bank/r8_firq // This pre-encodes the firq_s3 signal thats used in u_register_bank assign firq_not_user_mode_nxt = !user_mode_regs_load_nxt && status_bits_mode_nxt == FIRQ; // ======================================================== // Next State Logic // ======================================================== // this replicates the current value of the execute signal in the execute stage assign instruction_execute = conditional_execute ( condition_r, i_execute_status_bits[31:28] ); assign instruction_valid = (control_state == EXECUTE || control_state == PRE_FETCH_EXEC) || // when last instruction was multi-cycle instruction but did not execute // because condition was false then act like you're in the execute state (!instruction_execute && (control_state == PC_STALL1 || control_state == MEM_WAIT1 || control_state == COPRO_WAIT || control_state == SWAP_WRITE || control_state == MULT_PROC1 || control_state == MTRANS_EXEC1 || control_state == MTRANS_EXEC3 || control_state == MTRANS_EXEC3B ) ); always @* begin // default is to hold the current state control_state_nxt = control_state; // Note: The order is important here if ( control_state == RST_WAIT1 ) control_state_nxt = RST_WAIT2; if ( control_state == RST_WAIT2 ) control_state_nxt = EXECUTE; if ( control_state == INT_WAIT1 ) control_state_nxt = INT_WAIT2; if ( control_state == INT_WAIT2 ) control_state_nxt = EXECUTE; if ( control_state == COPRO_WAIT ) control_state_nxt = PRE_FETCH_EXEC; if ( control_state == PC_STALL1 ) control_state_nxt = PC_STALL2; if ( control_state == PC_STALL2 ) control_state_nxt = EXECUTE; if ( control_state == SWAP_WRITE ) control_state_nxt = SWAP_WAIT1; if ( control_state == SWAP_WAIT1 ) control_state_nxt = SWAP_WAIT2; if ( control_state == MULT_STORE ) control_state_nxt = PRE_FETCH_EXEC; if ( control_state == MTRANS5_ABORT ) control_state_nxt = PRE_FETCH_EXEC; if ( control_state == MEM_WAIT1 ) control_state_nxt = MEM_WAIT2; if ( control_state == MEM_WAIT2 || control_state == SWAP_WAIT2 ) begin if ( write_pc ) // writing to the PC!! control_state_nxt = PC_STALL1; else control_state_nxt = PRE_FETCH_EXEC; end if ( control_state == MTRANS_EXEC1 ) begin if (mtrans_instruction_nxt[15:0] != 16'd0) control_state_nxt = MTRANS_EXEC2; else // if the register list holds a single register control_state_nxt = MTRANS_EXEC3; end // Stay in State MTRANS_EXEC2 until the full list of registers to // load or store has been processed if ( control_state == MTRANS_EXEC2 && mtrans_num_registers == 5'd1 ) control_state_nxt = MTRANS_EXEC3; if ( control_state == MTRANS_EXEC3 ) control_state_nxt = MTRANS_EXEC4; if ( control_state == MTRANS_EXEC3B ) control_state_nxt = MTRANS_EXEC4; if ( control_state == MTRANS_EXEC4 ) begin if ( dabt ) // data abort control_state_nxt = MTRANS5_ABORT; else if (write_pc) // writing to the PC!! control_state_nxt = PC_STALL1; else control_state_nxt = PRE_FETCH_EXEC; end if ( control_state == MULT_PROC1 ) begin if (!instruction_execute) control_state_nxt = PRE_FETCH_EXEC; else control_state_nxt = MULT_PROC2; end if ( control_state == MULT_PROC2 ) begin if ( i_multiply_done ) if ( o_multiply_function[1] ) // Accumulate ? control_state_nxt = MULT_ACCUMU; else control_state_nxt = MULT_STORE; end if ( control_state == MULT_ACCUMU ) begin control_state_nxt = MULT_STORE; end // This should come at the end, so that conditional execution works // correctly if ( instruction_valid ) begin // default is to stay in execute state, or to move into this // state from a conditional execute state control_state_nxt = EXECUTE; if ( mem_op ) // load or store word or byte control_state_nxt = MEM_WAIT1; if ( write_pc ) control_state_nxt = PC_STALL1; if ( itype == MTRANS ) begin if ( mtrans_num_registers != 5'd0 ) begin // check for LDM/STM of a single register if ( mtrans_num_registers == 5'd1 ) control_state_nxt = MTRANS_EXEC3B; else control_state_nxt = MTRANS_EXEC1; end else control_state_nxt = MTRANS_EXEC3; end if ( itype == MULT ) control_state_nxt = MULT_PROC1; if ( itype == SWAP ) control_state_nxt = SWAP_WRITE; if ( itype == CORTRANS && !und_request ) control_state_nxt = COPRO_WAIT; // interrupt overrides everything else so its last if ( interrupt ) control_state_nxt = INT_WAIT1; end end // ======================================================== // Register Update // ======================================================== always @ ( posedge i_clk ) if (!i_fetch_stall) begin o_read_data <= i_read_data; o_read_data_alignment <= {i_execute_address[1:0], 3'd0}; abt_address_reg <= i_execute_address; iabt_reg <= i_iabt; adex_reg <= i_adex; abt_status_reg <= i_abt_status; status_bits_mode_r <= status_bits_mode_nxt; status_bits_irq_mask_r <= status_bits_irq_mask_nxt; status_bits_firq_mask_r <= status_bits_firq_mask_nxt; o_imm32 <= imm32_nxt; o_imm_shift_amount <= imm_shift_amount_nxt; o_shift_imm_zero <= shift_imm_zero_nxt; // when have an interrupt, execute the interrupt operation // unconditionally in the execute stage // ensures that status_bits register gets updated correctly // Likewise when in middle of multi-cycle instructions // execute them unconditionally condition_r <= instruction_valid && !interrupt ? condition_nxt : AL; o_exclusive_exec <= exclusive_exec_nxt; o_data_access_exec <= data_access_exec_nxt; o_rm_sel <= o_rm_sel_nxt; o_rds_sel <= o_rds_sel_nxt; o_rn_sel <= o_rn_sel_nxt; o_barrel_shift_amount_sel <= barrel_shift_amount_sel_nxt; o_barrel_shift_data_sel <= barrel_shift_data_sel_nxt; o_barrel_shift_function <= barrel_shift_function_nxt; o_alu_function <= alu_function_nxt; o_use_carry_in <= use_carry_in_nxt; o_multiply_function <= multiply_function_nxt; o_interrupt_vector_sel <= next_interrupt; address_sel_r <= address_sel_nxt; pc_sel_r <= pc_sel_nxt; o_byte_enable_sel <= byte_enable_sel_nxt; o_status_bits_sel <= status_bits_sel_nxt; o_reg_write_sel <= reg_write_sel_nxt; o_user_mode_regs_load <= user_mode_regs_load_nxt; o_firq_not_user_mode <= firq_not_user_mode_nxt; o_write_data_wen <= write_data_wen_nxt; o_base_address_wen <= base_address_wen_nxt; pc_wen_r <= pc_wen_nxt; o_reg_bank_wsel <= reg_bank_wsel_nxt; o_reg_bank_wen <= decode ( reg_bank_wsel_nxt ); o_status_bits_flags_wen <= status_bits_flags_wen_nxt; o_status_bits_mode_wen <= status_bits_mode_wen_nxt; o_status_bits_irq_mask_wen <= status_bits_irq_mask_wen_nxt; o_status_bits_firq_mask_wen <= status_bits_firq_mask_wen_nxt; o_copro_opcode1 <= instruction[23:21]; o_copro_opcode2 <= instruction[7:5]; o_copro_crn <= instruction[19:16]; o_copro_crm <= instruction[3:0]; o_copro_num <= instruction[11:8]; o_copro_operation <= copro_operation_nxt; o_copro_write_data_wen <= copro_write_data_wen_nxt; mtrans_r15 <= mtrans_r15_nxt; restore_base_address <= restore_base_address_nxt; control_state <= control_state_nxt; mtrans_reg_d1 <= mtrans_reg; mtrans_reg_d2 <= mtrans_reg_d1; end always @ ( posedge i_clk ) if ( !i_fetch_stall ) begin // sometimes this is a pre-fetch instruction // e.g. two ldr instructions in a row. The second ldr will be saved // to the pre-fetch instruction register // then when its decoded, a copy is saved to the saved_current_instruction // register if (itype == MTRANS) begin saved_current_instruction <= mtrans_instruction_nxt; saved_current_instruction_iabt <= instruction_iabt; saved_current_instruction_adex <= instruction_adex; saved_current_instruction_address <= instruction_address; saved_current_instruction_iabt_status <= instruction_iabt_status; end else if (saved_current_instruction_wen) begin saved_current_instruction <= instruction; saved_current_instruction_iabt <= instruction_iabt; saved_current_instruction_adex <= instruction_adex; saved_current_instruction_address <= instruction_address; saved_current_instruction_iabt_status <= instruction_iabt_status; end if (pre_fetch_instruction_wen) begin pre_fetch_instruction <= o_read_data; pre_fetch_instruction_iabt <= iabt_reg; pre_fetch_instruction_adex <= adex_reg; pre_fetch_instruction_address <= abt_address_reg; pre_fetch_instruction_iabt_status <= abt_status_reg; end end always @ ( posedge i_clk ) if ( !i_fetch_stall ) begin irq <= i_irq; firq <= i_firq; if ( control_state == INT_WAIT1 && status_bits_mode_r == SVC ) begin dabt_reg <= 1'd0; end else begin dabt_reg <= dabt_reg || i_dabt; end dabt_reg_d1 <= dabt_reg; end assign dabt = dabt_reg || i_dabt; // ======================================================== // Decompiler for debugging core - not synthesizable // ======================================================== //synopsys translate_off `include "debug_functions.vh" a23_decompile u_decompile ( .i_clk ( i_clk ), .i_fetch_stall ( i_fetch_stall ), .i_instruction ( instruction ), .i_instruction_valid ( instruction_valid ), .i_instruction_execute ( instruction_execute ), .i_instruction_address ( instruction_address ), .i_interrupt ( {3{interrupt}} & next_interrupt ), .i_interrupt_state ( control_state == INT_WAIT2 ), .i_instruction_undefined ( und_request ), .i_pc_sel ( pc_sel_r ), .i_pc_wen ( pc_wen_r )); wire [(15*8)-1:0] xCONTROL_STATE; wire [(15*8)-1:0] xMODE; assign xCONTROL_STATE = control_state == RST_WAIT1 ? "RST_WAIT1" : control_state == RST_WAIT2 ? "RST_WAIT2" : control_state == INT_WAIT1 ? "INT_WAIT1" : control_state == INT_WAIT2 ? "INT_WAIT2" : control_state == EXECUTE ? "EXECUTE" : control_state == PRE_FETCH_EXEC ? "PRE_FETCH_EXEC" : control_state == MEM_WAIT1 ? "MEM_WAIT1" : control_state == MEM_WAIT2 ? "MEM_WAIT2" : control_state == PC_STALL1 ? "PC_STALL1" : control_state == PC_STALL2 ? "PC_STALL2" : control_state == MTRANS_EXEC1 ? "MTRANS_EXEC1" : control_state == MTRANS_EXEC2 ? "MTRANS_EXEC2" : control_state == MTRANS_EXEC3 ? "MTRANS_EXEC3" : control_state == MTRANS_EXEC3B ? "MTRANS_EXEC3B" : control_state == MTRANS_EXEC4 ? "MTRANS_EXEC4" : control_state == MTRANS5_ABORT ? "MTRANS5_ABORT" : control_state == MULT_PROC1 ? "MULT_PROC1" : control_state == MULT_PROC2 ? "MULT_PROC2" : control_state == MULT_STORE ? "MULT_STORE" : control_state == MULT_ACCUMU ? "MULT_ACCUMU" : control_state == SWAP_WRITE ? "SWAP_WRITE" : control_state == SWAP_WAIT1 ? "SWAP_WAIT1" : control_state == SWAP_WAIT2 ? "SWAP_WAIT2" : control_state == COPRO_WAIT ? "COPRO_WAIT" : "UNKNOWN " ; assign xMODE = mode_name ( status_bits_mode_r ); always @( posedge i_clk ) if (control_state == EXECUTE && ((instruction[0] === 1'bx) || (instruction[31] === 1'bx))) begin `TB_ERROR_MESSAGE $display("Instruction with x's =%08h", instruction); end //synopsys translate_on endmodule