5.5 修改OpenMIPS以实现逻辑、位移操作和空指令
为了实现逻辑、位移操作与空指令，需要修改ID和EX模块。
5.5.1 修改译码阶段的ID模块
修改宏定义defines.v
defines.v +=
/**
EXE_* 功能码 或 指令码
**/
`define EXE_AND 6'b100100
`define EXE_OR 6'b100101
`define EXE_XOR 6'b100110
`define EXE_NOR 6'b100111
`define EXE_ANDI 6'b001100
`define EXE_ORI 6'b001101
`define EXE_XORI 6'b001110
`define EXE_LUI 6'b001111
`define EXE_SLL 6'b000000
`define EXE_SLLV 6'b000100
`define EXE_SRL 6'b000010
`define EXE_SRLV 6'b000110
`define EXE_SRA 6'b000011
`define EXE_SRAV 6'b000111
`define EXE_SYNC 6'b001111
`define EXE_PREF 6'b110011
`define EXE_SPECIAL_INST 6'b000000
以下是对指令编码和指令的映射算法：
修改后的代码如下：
`include "defines.h"
module id
(
input wire rst,
input wire[`InstAddrBus] pc_i,
input wire[`InstBus] inst_i,
//处于执行阶段的指令要写入的目的寄存器信息
input wire ex_wreg_i,
input wire[`RegBus] ex_wdata_i,
input wire[`RegAddrBus] ex_wd_i,
//处于访存阶段的指令要写入的目的寄存器信息
input wire mem_wreg_i,
input wire[`RegBus] mem_wdata_i,
input wire[`RegAddrBus] mem_wd_i,
//从regfile读取的数据
input wire[`RegBus] reg1_data_i,
input wire[`RegBus] reg2_data_i,
//送到regfile的信息
output reg reg1_read_o,
output reg reg2_read_o,
output reg[`RegAddrBus] reg1_addr_o,
output reg[`RegAddrBus] reg2_addr_o,
//送到执行阶段的信息
output reg[`AluOpBus] aluop_o,
output reg[`AluSelBus] alusel_o,
output reg[`RegBus] reg1_o,
output reg[`RegBus] reg2_o,
output reg[`RegAddrBus] wd_o,
output reg wreg_o
);
wire[5:0] op = inst_i[31:26];
wire[4:0] op2 = inst_i[10:6];
wire[5:0] op3 = inst_i[5:0];
wire[4:0] op4 = inst_i[20:16];
reg[`RegBus] imm;
reg instvalid;
always @ (*) begin
if (rst == `RstEnable) begin
aluop_o <= `EXE_NOP_OP;
alusel_o <= `EXE_RES_NOP;
wd_o <= `NOPRegAddr;
wreg_o <= `WriteDisable;
instvalid <= `InstValid;
reg1_read_o <= 1'b0;
reg2_read_o <= 1'b0;
reg1_addr_o <= `NOPRegAddr;
reg2_addr_o <= `NOPRegAddr;
imm <= 32'h0;
end else begin
aluop_o <= `EXE_NOP_OP;
alusel_o <= `EXE_RES_NOP;
wd_o <= inst_i[15:11];
wreg_o <= `WriteDisable;
instvalid <= `InstInvalid;
reg1_read_o <= 1'b0;
reg2_read_o <= 1'b0;
reg1_addr_o <= inst_i[25:21];
reg2_addr_o <= inst_i[20:16];
imm <= `ZeroWord;
case (op)
`EXE_SPECIAL_INST: begin
case (op2)
5'b00000: begin
case (op3)
`EXE_OR:begin
wreg_o <= `WriteEnable;
aluop_o <= `EXE_OR_OP;
alusel_o <= `EXE_RES_LOGIC;
reg1_read_o <= 1'b1;
reg2_read_o <= 1'b1;
instvalid <= `InstValid;
end
`EXE_AND:begin
wreg_o <= `WriteEnable;
aluop_o <= `EXE_AND_OP;
alusel_o <= `EXE_RES_LOGIC;
reg1_read_o <= 1'b1;
reg2_read_o <= 1'b1;
instvalid <= `InstValid;
end
`EXE_XOR:begin
wreg_o <= `WriteEnable;
aluop_o <= `EXE_XOR_OP;
alusel_o <= `EXE_RES_LOGIC;
reg1_read_o <= 1'b1;
reg2_read_o <= 1'b1;
instvalid <= `InstValid;
end
`EXE_NOR:begin
wreg_o <= `WriteEnable;
aluop_o <= `EXE_NOR_OP;
alusel_o <= `EXE_RES_LOGIC;
reg1_read_o <= 1'b1;
reg2_read_o <= 1'b1;
instvalid <= `InstValid;
end
`EXE_SLLV:begin
wreg_o <= `WriteEnable;
aluop_o <= `EXE_SLL_OP;
alusel_o <= `EXE_RES_SHIFT;
reg1_read_o <= 1'b1;
reg2_read_o <= 1'b1;
instvalid <= `InstValid;
end
`EXE_SRLV: begin
wreg_o <= `WriteEnable;
aluop_o <= `EXE_SRL_OP;
alusel_o <= `EXE_RES_SHIFT;
reg1_read_o <= 1'b1;
reg2_read_o <= 1'b1;
instvalid <= `InstValid;
end
`EXE_SRAV:begin
wreg_o <= `WriteEnable;
aluop_o <= `EXE_SRA_OP;
alusel_o <= `EXE_RES_SHIFT;
reg1_read_o <= 1'b1;
reg2_read_o <= 1'b1;
instvalid <= `InstValid;
end
`EXE_SYNC: begin
wreg_o <= `WriteDisable;
aluop_o <= `EXE_NOP_OP;
alusel_o <= `EXE_RES_NOP;
reg1_read_o <= 1'b0;
reg2_read_o <= 1'b1;
instvalid <= `InstValid;
end
default:begin end
endcase
end
default: begin end
endcase
end
`EXE_ORI:begin //ORI指令
wreg_o <= `WriteEnable;
aluop_o <= `EXE_OR_OP;
alusel_o <= `EXE_RES_LOGIC;
reg1_read_o <= 1'b1;
reg2_read_o <= 1'b0;
imm <= {16'h0, inst_i[15:0]};
wd_o <= inst_i[20:16];
instvalid <= `InstValid;
end
`EXE_ANDI:begin
wreg_o <= `WriteEnable;
aluop_o <= `EXE_AND_OP;
alusel_o <= `EXE_RES_LOGIC;
reg1_read_o <= 1'b1;
reg2_read_o <= 1'b0;
imm <= {16'h0, inst_i[15:0]};
wd_o <= inst_i[20:16];
instvalid <= `InstValid;
end
`EXE_XORI:begin
wreg_o <= `WriteEnable;
aluop_o <= `EXE_XOR_OP;
alusel_o <= `EXE_RES_LOGIC;
reg1_read_o <= 1'b1;
reg2_read_o <= 1'b0;
imm <= {16'h0, inst_i[15:0]};
wd_o <= inst_i[20:16];
instvalid <= `InstValid;
end
`EXE_LUI:begin
wreg_o <= `WriteEnable;
aluop_o <= `EXE_OR_OP;
alusel_o <= `EXE_RES_LOGIC;
reg1_read_o <= 1'b1;
reg2_read_o <= 1'b0;
imm <= {inst_i[15:0], 16'h0};
wd_o <= inst_i[20:16];
instvalid <= `InstValid;
end
`EXE_PREF:begin
wreg_o <= `WriteDisable;
aluop_o <= `EXE_NOP_OP;
alusel_o <= `EXE_RES_NOP;
reg1_read_o <= 1'b0;
reg2_read_o <= 1'b0;
instvalid <= `InstValid;
end
default:begin end
endcase //case op
if (inst_i[31:21] == 11'b00000000000) begin
if (op3 == `EXE_SLL) begin
wreg_o <= `WriteEnable;
aluop_o <= `EXE_SLL_OP;
alusel_o <= `EXE_RES_SHIFT;
reg1_read_o <= 1'b0;
reg2_read_o <= 1'b1;
imm[4:0] <= inst_i[10:6];
wd_o <= inst_i[15:11];
instvalid <= `InstValid;
end else if ( op3 == `EXE_SRL ) begin
wreg_o <= `WriteEnable;
aluop_o <= `EXE_SRL_OP;
alusel_o <= `EXE_RES_SHIFT;
reg1_read_o <= 1'b0;
reg2_read_o <= 1'b1;
imm[4:0] <= inst_i[10:6];
wd_o <= inst_i[15:11];
instvalid <= `InstValid;
end else if ( op3 == `EXE_SRA ) begin
wreg_o <= `WriteEnable;
aluop_o <= `EXE_SRA_OP;
alusel_o <= `EXE_RES_SHIFT;
reg1_read_o <= 1'b0;
reg2_read_o <= 1'b1;
imm[4:0] <= inst_i[10:6];
wd_o <= inst_i[15:11];
instvalid <= `InstValid;
end
end
end //if
end //always
endmodule
AND指令的译码过程：
ANDI指令的译码过程：
SLLV指令的译码过程
LUI指令的译码过程
SLL指令的译码过程
5.5.2 修改执行阶段的EX模块
`include "defines.v"
module ex(
input wire rst,
//送到执行阶段的信息
input wire[`AluOpBus] aluop_i,
input wire[`AluSelBus] alusel_i,
input wire[`RegBus] reg1_i,
input wire[`RegBus] reg2_i,
input wire[`RegAddrBus] wd_i,
input wire wreg_i,
output reg[`RegAddrBus] wd_o,
output reg wreg_o,
output reg[`RegBus] wdata_o
);
reg[`RegBus] logicout; //保存逻辑运算结果
reg[`RegBus] shiftres; //保存位移运算结果
//进行逻辑运算
always @ (*) begin
if(rst == `RstEnable) begin
logicout <= `ZeroWord;
end else begin
case (aluop_i)
`EXE_OR_OP: begin logicout <= reg1_i | reg2_i; end
`EXE_AND_OP:begin logicout <= reg1_i & reg2_i; end
`EXE_NOR_OP:begin logicout <= ~(reg1_i |reg2_i);end
`EXE_XOR_OP:begin logicout <= reg1_i ^ reg2_i; end
default: begin logicout <= `ZeroWord; end
endcase
end //if
end //always
//进行位移运算
always @ (*) begin
if(rst == `RstEnable) begin
shiftres <= `ZeroWord;
end else begin
case (aluop_i)
`EXE_SLL_OP:begin shiftres <= reg2_i << reg1_i[4:0]; end
`EXE_SRL_OP:begin shiftres <= reg2_i >> reg1_i[4:0]; end
`EXE_SRA_OP:begin shiftres <= ({32{reg2_i[31]}} << (6'd32-{1'b0, reg1_i[4:0]})) | reg2_i >> reg1_i[4:0]; end
default:begin shiftres <= `ZeroWord; end
endcase
end //if
end //always
//根据alusel_i选择最终的运算结果
always @ (*) begin
wd_o <= wd_i;
wreg_o <= wreg_i;
case (alusel_i)
`EXE_RES_LOGIC:begin wdata_o <= logicout; end
`EXE_RES_SHIFT:begin wdata_o <= shiftres; end
default:begin wdata_o <= `ZeroWord; end
endcase
end
endmodule
来源：https://www.cnblogs.com/ycc1997/p/12210149.html