一、 实验要求
设计并实现一个多周期MIPS CPU，并满足如下要求：
1）仅允许使用一个存储器
2）实现六条指令：addi、add、lw、sw、bgtz、j
3）对给予的斐波那契数列例程进行测试
二、 实验原理
1）数据通路：
上图中不包含j指令的数据通路，添加后如下：
2）有限状态机（FSM）——状态图
三、 实验内容
1.生成IP核
为了使编码简单，这里的ram采用的是异步读，同步写，宽度32bit，深度为64.
2.主要代码分析
module top(
input clk,
input reset,
output [31:0] pc_in,
output [31:0] pc_out,
output pc_write
);
wire [2:0]alu_op;
wire [1:0]pc_src;
wire alu_src_a;
wire [1:0]alu_src_b;
wire mem_toreg;
wire reg_write;
wire reg_dst;
wire [4:0]rd;
wire [31:0]data_out;
wire [31:0]data_out1;
wire [31:0]data_out2;
wire [31:0]data_out_a;
wire [31:0]data_out_b;
wire [31:0]data_out_out;
wire [31:0]alu_out;
wire [31:0]alu_out_out;
wire [31:0]data_write;
wire [31:0]src_a;
wire [31:0]src_b;
wire [31:0]imm;
wire mem_write;
wire ir_write;
wire [31:0]inst;
wire [31:0]addr;
wire branch_2;
wire pc_write_2;
branchand band(branch,data_out_a,branch_2);
branchor bor(branch_2,pc_write,pc_write_2);
pc pc(clk, pc_in, pc_write_2, reset, pc_out);
dataselect_32_bitaddrmux(pc_out,alu_out_out,i_or_d,addr);
ram ram(addr,data_out2,clk,mem_write,data_out);
ir ins(data_out,clk,ir_write,inst);
dataselect_5_bitregdst(inst[20:16],inst[15:11],reg_dst,rd);
data d(data_out, clk,data_out_out);
dataselect_32_bitdatamux(alu_out,data_out_out,mem_toreg,data_write);
regfilere(inst[25:21],inst[20:16],data_write,rd,reg_write,clk,data_out1, data_out2);
ab ab(data_out1,data_out2,clk,data_out_a,data_out_b);
dataselect_32_bitA(pc_out,data_out_a,alu_src_a,src_a);
signextension im(inst[15:0],imm);
dataselect_32_bit_4dataB(data_out_b,32'b1,imm,imm,alu_src_b,src_b);
alu a(src_a,src_b,alu_op,alu_out);
data aluout(alu_out,clk,alu_out_out);
dataselect_32_bit_3data pcsrc(alu_out,alu_out_out,inst[25:0],pc_src, pc_in);
controlunitcon(inst[31:26],reset,5'b0,clk,pc_write,branch,pc_src,alu_op,alu_src_a,alu_src_b,reg_write,i_or_d,ir_write,mem_write,mem_toreg,reg_dst);
endmodule********************************************************************************************
modulecontrolunit( //控制模块，用于译码产生控制信号，包含两个子模块
input [5:0] opcode,
input reset,
input [5:0] funct, //本实验只考虑add所以暂时用不到这个字段
input clk,
output pc_write,
output branch,
output [1:0]pc_src,
output [2:0] alu_op,
output alu_src_a,
output [1:0] alu_src_b,
output reg_write,
output i_or_d,
output ir_write,
output mem_write,
output mem_toreg,
output reg_dst
);
reg[3:0]now_state = 4'b0; //当前状态
wire[3:0]next_state; //下一个状态
always@(posedgeclk)
if(~reset)begin now_state = 5'b0; end
else
begin
now_state = next_state; //根据子模块1的运算结果进行状态转换
end
nextstatenext(now_state,opcode,next_state);//子模块1，用于运算下一个状态
control_outputout( //子模块2，用于根据当前状态进行输出
opcode,
now_state,
pc_write,
branch,
pc_src,
alu_op,
alu_src_a,
alu_src_b,
reg_write,
i_or_d,
ir_write,
mem_write,
mem_toreg,
reg_dst);
endmodule********************************************************************************************
module nextstate(i_state,opcode, next_state);
input [3:0]i_state;
input [5:0]opcode;
output reg[3:0]next_state;
parameter [3:0] s0 = 4'd0,
s1 = 4'd1,
s2 = 4'd2,
s3 = 4'd3,
s4 = 4'd4,
s5 = 4'd5,
s6 = 4'd6,
s7 = 4'd7,
s8 = 4'd8,
s9 = 4'd9,
s10 = 4'd10,
s11 = 4'd11;
always @(*)
begin
case (i_state)
s0: next_state = s1;
s1:
begin
case (opcode)
6'b000000: next_state= s6; //add
6'b001000: next_state = s9; //addi
6'b100011: next_state = s2; //lw
6'b101011: next_state = s2; //sw
6'b000010: next_state = s11; //jump
6'b000111: next_state = s8; //bgtz
endcase
end
s2:
begin
case (opcode)
6'b100011: next_state = s3; //lw
6'b101011: next_state = s5; //sw
endcase
end
s3: next_state = s4;
s4: next_state = s0;
s5: next_state = s0;
s6: next_state = s7;
s7: next_state = s0;
s8:next_state = s0;
s9:next_state = s10;
s10:next_state = s0;
s11:next_state = s0;
endcase
end
endmodule********************************************************************************************
module control_output( //根据当前state进行输出
input[5:0] opcode,
input[3:0] state,
output reg pc_write,
output reg branch,
output reg [1:0]pc_src,
output reg [2:0] alu_op,
output reg alu_src_a,
output reg [1:0]alu_src_b,
outputreg reg_write,
output reg i_or_d,
output reg ir_write,
output reg mem_write,
output reg mem_toreg,
output reg reg_dst
);
parameter [3:0] s0 = 4'd0,
s1 = 4'd1,
s2 = 4'd2,
s3 = 4'd3,
s4 = 4'd4,
s5 = 4'd5,
s6 = 4'd6,
s7 = 4'd7,
s8 = 4'd8,
s9 = 4'd9,
s10 = 4'd10,
s11 = 4'd11;
always @(state)
begin
case(state)
s0:
begin
pc_write= 1;
branch= 0;
pc_src= 2'b00;
alu_op= 2'b01; //alu的操作码与ppt给定的不同
//因为alu模块编写的不同进行了调整
alu_src_a= 0;
alu_src_b= 2'b01;
reg_write= 0;
i_or_d= 0;
ir_write= 1;
mem_write= 0;
mem_toreg= 0;
reg_dst= 0;
end
s1:
begin
pc_write= 0;
alu_src_b= 2'b11;
ir_write= 0;
end
s2:
begin
alu_op= 2'b01;
alu_src_a= 1;
alu_src_b= 2'b10;
end
s3:
begin
i_or_d= 1;
end
s4:
begin
reg_write= 1;
mem_toreg= 1;
reg_dst= 0;
end
s5:
begin
i_or_d= 1;
mem_write= 1;
//pc_write = 1;
end
s6:
begin
alu_op= 2'b01;
alu_src_a= 1;
alu_src_b= 2'b00;
end
s7:
begin
reg_write= 1;
mem_toreg= 0;
reg_dst= 1;
end
s8:
begin
branch= 1;
pc_src= 2'b01;
alu_op= 2'b10;
alu_src_a= 1;
alu_src_b= 2'b10;
end
s9:
begin
alu_op= 2'b01;
alu_src_a= 1;
alu_src_b= 2'b10;
end
s10:
begin
reg_write= 1;
mem_toreg= 0;
reg_dst= 0;
end
s11:
begin
pc_write= 1;
pc_src= 2'b10;
end
endcase
end
endmodule********************************************************************************************
其余模块较为简单或者见之前实验报告，此处略去
3.coe文件编写
Coe文件中存储了待运行的代码以及相关的数据，这里根据本人的设计做了响应的修改
下面是coe文件的具体内容，以及对应产生的内存数据：
4.仿真
波形图看起来比较不直观，这里主要观察指令以及状态的跳转是否正确：
确认指令执行无误后，观察内存里的内容，如下（十进制）：
四、 实验分析和总结
本实验于单周期的cpu相比，数据通路上发生了一些较为明显的变化，首先指令和数据不再分开存放，其次增加了一定数量的寄存器存储关键数据，这是由多周期指令特性决定的。
然后，多周期cpu的设计运用了有限状态机的思想，这在单周期cpu里是没有体现的，每个指令再不同的时钟周期里，其控制信号完全不同，所以需要状态机来控制状态的条状，并且根据不同指令的不同状态来决定控制信号的输出。