/// LSU EE 3755 – Fall 2009 -- Computer
Organization.
//
/// MIPS Processor Functional Unit.
//
// Implements a small subset of MIPS32 instructions and features.
/
//
The intent is to demonstrate basic MIPS
CPU functionality,
// to clarify the concept of data path we just
covered.
module
proc(exc,clk);
input clk;
output exc;
reg [31:0] pc, npc, nnpc;
reg [31:0] ir;
reg [5:0] opcode, func;
reg [4:0] rs, rt, rd, sa;
reg [15:0] immed;
reg [25:0] ii;
reg [7:0] mem ['h400000:'h400200];
reg [31:0] gpr [0:31];
reg [31:0] simmed, uimmed;
reg [7:0] temp;
parameter
F_add = 6'h20;
parameter
F_sll = 6'h0;
parameter
F_srl = 6'h2;
parameter
F_sub = 6'h22;
parameter
F_or =
6'h25;
parameter
F_jr =
6'h8;
parameter
O_tyr =
6'h0;
parameter
O_addi = 6'h8;
parameter
O_j =
6'h2;
parameter
O_jal =
6'h3;
parameter
O_beq =
6'h4;
parameter
O_bne =
6'h5;
parameter
O_slti = 6'ha;
parameter
O_andi = 6'hc;
parameter
O_ori =
6'hd;
parameter
O_lui =
6'hf;
parameter
O_lw =
6'h23;
parameter
O_lbu =
6'h24;
parameter
O_lb =
6'h20;
parameter
O_sw =
6'h2b;
parameter
O_sb =
6'h28;
always @( posedge clk ) begin
ir = {mem[pc],mem[pc+1],mem[pc+2],mem[pc+3]};
{opcode, rs, rt, rd, sa,
func} = ir;
immed = ir[15:0];
ii = ir[25:0];
simmed = {immed[15] ? 16'hffff : 16'h0, immed};
uimmed = {
16'h0, immed };
nnpc = npc + 4; //
Reassigned below.
case( opcode )
O_tyr:
case( func )
F_add: gpr[rd] = gpr[rs]
+ gpr[rt];
F_sub: gpr[rd] = gpr[rs]
- gpr[rt];
F_sll: gpr[rd] = gpr[rt]
<< sa;
F_jr: nnpc = gpr[rs];
default: $stop;
endcase
O_addi: gpr[rt] = gpr[rs] + simmed;
O_andi: gpr[rt] = gpr[rs] & uimmed;
O_ori: gpr[rt] = gpr[rs]
| uimmed;
O_lui: gpr[rt] = {immed,16'h0};
O_bne: if( gpr[rt] != gpr[rs] ) nnpc = npc + ( simmed << 2 );
O_j: nnpc =
{pc[31:28],ii,2'd0};
O_jal: begin gpr[31] = nnpc; nnpc = {pc[31:28],ii,2'd0};
end
O_lbu: gpr[rt] = {24'b0, mem[`A(gpr[rs]+simmed)]};
O_lb:
begin
temp = mem[`A(gpr[rs]+simmed)];
gpr[rt] = {temp[7] ? 24'hffffff : 24'h0, temp};
end
O_sb: mem[`A(gpr[rs]+simmed)]= gpr[rt];
default: $stop;
endcase
gpr[0] = 0;
pc = npc;
npc = nnpc;
end
endmodule