Verilog Code for 16bit RISC Processor

16BIT RISC PROCESSOR

Hola Amigos
I have designed a 16bit RISC processor designed with Xilinx iSim ans iSim simulator. RISC stands for Reduced Instruction Set Computer which is small microprocessor designed to favour small tasks and compute instructions with less time for the execution process. 
Common RISC processors that you would see around are ARM, MIPS, IBM Pc. 

Why was RISC introduced ?
As compared with CISC (Complex Instruction Set Computer) which takes a complex time to execute the instructions was reducing the performance of computing where the speed was drowning when CPU contacts the data memory. Hence another alternative was set in motion and that was RISC architecture.

Coming down to my 16bit processor.
ALU  Code-
**************************************************************************************

module ALU(ain,bin,func,result,z);
input [7:0]ain;
input [7:0]bin;
output reg[7:0]result;
reg carry,temp=0;
input [3:0]func;
output reg z;
//wire [7:0]result;
//assign n = result[7];
always @(ain or bin)begin
if(func==4'b0000)begin
{temp,result} = ain + bin;
carry = temp;
if(result==0)
z=1;
end
else if(func==4'b0001)begin
{temp,result} = ain - bin;
carry = temp;
if(result==0)
z=1;
end
else if(func==4'b0010)begin
{temp,result} = ain + 1;
carry = temp;
if(result==0)
z=1;
end
else if(func==4'b0011)begin
{temp,result} = ain - 1;
carry = temp;
if(result==0)
z=1;
end
else if(func==4'b0100)begin
result = ain | bin;
carry = 0;
if(result==0)
z=1;end //OR
else if(func==4'b0101)begin 
result = ain & bin;
carry = 0;
if(result==0)
z=1;end //AND
else if(func==4'b0110)begin 
result = ain^bin;
carry = 0;
if(result==0)
z=1;end //XOR
else if(func==4'b0111)begin 
result[0] = ~(ain[0]&bin[0]);
result[1] = ~(ain[1]&bin[1]);
result[2] = ~(ain[2]&bin[2]);
result[3] = ~(ain[3]&bin[3]);
result[4] = ~(ain[4]&bin[4]);
result[5] = ~(ain[5]&bin[5]);
result[6] = ~(ain[6]&bin[6]);
result[7] = ~(ain[7]&bin[7]);
carry = 0;
if(result==0)
z=1;end //NAND
else if(func==4'b1000)begin 
result[0] = ~ain[0];
result[1] = ~ain[1];
result[2] = ~ain[2];
result[3] = ~ain[3];
result[4] = ~ain[4];
result[5] = ~ain[5];
result[6] = ~ain[6];
result[7] = ~ain[7];
carry = 0;
if(result==0)
z=1;end //NOT
else begin 
result = 4'bxxxx;
carry = 0;
end //Default
if(result==0)
z = 1'b1;
else
z = 0;
end

endmodule

Instruction Memory
**************************************************************************************
module instruction(address,clk,opcode,jump,jiz,addA,addB,write_add,iformat,im_select);
input [15:0]address;
input clk,im_select;
output reg[3:0]opcode;
output reg[11:0] jump;
output reg[7:0] jiz;
output reg[3:0] addA;
output reg[3:0] addB;
output reg[3:0] write_add;
output reg[3:0] iformat;
reg [3:0]dest;
reg [15:0]instruction;
reg [15:0] imem[0:15];
initial begin
imem[2]<=16'b0000_0000_0000_0101; 
imem[1]<=16'b0001_0010_0011_0011; 
imem[3]<=16'b0010_0100_0010_0011;
imem[0]<=16'b0010_0000_0000_0101;
imem[4]<=16'b0010_0111_0010_0011;
imem[5]<=16'b0011_0010_0011_0010;
imem[6]<=16'b0110_0001_0001_0011;
imem[7]<=16'b0001_0110_0001_0011;
imem[8]<=16'b0110_0001_0011_0001; 
end
always @(im_select)begin
if(im_select==1)begin
dest=write_add;
instruction = imem[address];
opcode = instruction[15:12];
jump = instruction[11:0];
jiz = instruction[7:0];
addA = instruction[11:8];
addB = instruction[7:4];
write_add = instruction[3:0];
iformat = instruction[3:0];
end
end

endmodule

Register File
**************************************************************************************
module Register(reg_wrt,readA,clk,readB,dest,data,readA_out,readB_out);
input reg_wrt;
input [3:0]readA,readB,dest;
input [7:0]data;
input clk;
reg [7:0] Register [0:15];
initial begin
Register[0]=0;//R0 alwayscontains zero
Register[1]=2;  //Random values stored
Register[2]=4;
Register[3]=6;
Register[4]=8;
Register[5]=10; // You can change any value within this initial block
Register[6]=12;
Register[7]=14;
end
output reg [7:0]readA_out,readB_out;
always @(posedge clk)begin
readA_out <= Register[readA];
readB_out <= Register[readB];
if(reg_wrt==1)
Register[dest]=data;
end

endmodule

RAM (Datamemory) 
**************************************************************************************
module RAM(address,clk,data_in,data_out,re,wr);
input [7:0]address;
input [7:0]data_in;
input clk,re,wr;
output [7:0]data_out;
reg[7:0] mem [0:30];
reg[7:0] data;
assign data_out = data;
initial
mem[16]=25;
always @(posedge clk)begin
if(wr)begin
mem[address] = data_in;
end
end
always @(address or re)begin
if(re)begin
data = mem[address];
end
end

endmodule

Program Counter
**************************************************************************************
module PC(in,clk,out,pc_sel,reset);
input [15:0]in;
input clk,reset,pc_sel;
output reg[15:0]out;
initial 
out = 0;
always @(posedge clk)begin
if(reset==1)
out <= 16'bx;
else if(pc_sel==1 && in<50)
out <= in+1;
else if(pc_sel==0)
out <= in;
end

endmodule

Multiplexers

**************************************************************************************

module Mux1(a,b,sel,c);

input [3:0] a,b;

input sel;

output reg [3:0]c;

always @(*)begin

if(sel==0)

c = a;

else

c = b;

end

endmodule

module Mux2(a,b,sel,c);

input [7:0] a,b;

input [1:0]sel;

output reg [7:0]c;

always @(*)begin

if(sel==2'b0)

c = a;

else if(sel==2'b01)

c = b;

else if(sel==2'b10)

c = 8'b0;

end

endmodule

module Mux3(a,b,sel,c);

input [15:0] a,b;

input sel;

output reg [15:0]c;

always @(*)begin

if(sel==0)

c = a;

else

c = b;

end

endmodule

Sign Extend

**************************************************************************************

module sign(a,b);

input [3:0]a;

output reg[7:0]b;

always @(a or b)begin

if(a[3]==1)

b = {4'b1111,a};

else

b = {4'b0000,a};

end

endmodule

Latch

**************************************************************************************

module lat(in,out,clk);

input [7:0] in;

input clk;

output reg[7:0] out;

reg [7:0]memdataout;

always @ (posedge clk)

out=in;

endmodule

Datapath

**************************************************************************************

module datapath(alu_op,opcode,clk,carry,sel1,sel2,sel3,sel5,sel6,re,wr,reg_wrt,reset,pc_sel,im_select,branch);

input clk;

output carry;
input [1:0]sel2;

input sel1,sel3,sel5,sel6,re,wr;

input reg_wrt;

input reset;

output [3:0]opcode;

input [3:0]alu_op;

input im_select;

input branch,pc_sel;

wire [7:0] shift;

wire [15:0] next_pc;

wire [15:0] next_alu_out,jump_add;

wire [11:0] jump;

and (sel4,branch,zero);

wire [15:0]op3,out;

wire [15:0]pc_out;

wire [3:0]iformat,addA,addB,write_add,out1;

wire [7:0]data_out;

wire [7:0]result;

wire [7:0]regData,aluMux;

wire [7:0] dataA,dataB,xtended,out2,latchout;

Mux2 alu(dataA,8'bx,sel5,aluMux);

PC programcounter(op3,clk,pc_out,pc_sel,reset);

instruction im(pc_out,clk,opcode,jump,addA,addB,write_add,iformat,pc_sel);

Mux1 multi1(addB,write_add,sel1,out1);

Register regfile(reg_wrt,addA,clk,addB,out1,regData,dataA,dataB);

sign xtend(iformat,xtended);

lat latch(xtended,latchout,clk);

Mux2 multi2(dataB,latchout,sel2,out2);

ALU alux(aluMux,out2,alu_op,result,zero);

RAM datamemory(result,clk,dataB,data_out,re,wr);

Mux2 multi3(result,data_out,sel3,regData);

//assign next_pc = pc_out+1'b1;

assign next_alu_out = latchout + pc_out;

assign jump_add = {pc_out[15:12],jump}; 

Mux3 multi4(pc_out,next_alu_out,sel4,out);

Mux3 multi5(jump_add,out,sel6,op3);

endmodule

Control Unit

**************************************************************************************

module control(alu_op,opcode,clk,carry,reset,reg_wrt,re,wr,Mux1,Mux2,Mux3,MuxAlu,Mux5,branch,pc_sel,im_select);

input clk,carry,reset;

input [3:0] opcode;

output reg[3:0]alu_op;

output reg reg_wrt,re,wr,Mux1,Mux3,MuxAlu,Mux5,branch,pc_sel,im_select;
output reg[1:0]Mux2;

reg [3:0]pstate,nstate;

parameter s0 = 4'b0000,s1 = 4'b0001, s2=4'b0010, s3=4'b0011, s4=4'b0100, s5=4'b0101, s6=4'b0110, s7=4'b0111, s11=4'b1000;

initial

pstate = s0;

always @(posedge clk)begin

case(pstate)

//*********************************************************************************************************************

s0:begin  //DO NOT MODIFY INSTRUCTION FETCH  //

reg_wrt<=1'b0;

re<=1'b0;

wr<=1'b0;

Mux1<=1'b0;

Mux2<=1'b1;

Mux3<=1'b0;

Mux3<=1'b1;

Mux5<=1'b1;

alu_op<=4'bxxxx;

MuxAlu<=1'b1;

branch<=1'b0;

pc_sel<=1'b1;

im_select<=1'b1;

pstate<=s1;

end

//*********************************************************************************************************************

s1:begin  // DO NOT MODIFY DECODE STAGE  //

case(opcode)

4'b0000:begin

alu_op<=4'b0;

reg_wrt<=1'b1;

re<=1'b0;

wr<=1'b0;

Mux1<=1'b1;

Mux2<=1'b0;

Mux3<=1'b0;

Mux5<=1'b1;

MuxAlu<=1'b0;

branch<=1'b0;

pc_sel<=1'b0;

im_select<=1'b1;

pstate<=s0;

end

//*********************************************************************************************************************

4'b0001:begin  /* DO NOT MODIFY R-FORMAT STARTS HERE */

alu_op<=4'b0001;

reg_wrt<=1'b1;

re<=1'b0;

wr<=1'b0;

Mux1<=1'b1;

Mux2<=2'b0;

Mux3<=1'b0;

Mux5<=1'b1;

MuxAlu<=1'b0;

branch<=1'b0;

pc_sel<=1'b0;

im_select<=1'b1;

pstate<=s0;

end

//*********************************************************************************************************************

4'b0010:begin

alu_op<=4'b0010;

reg_wrt<=1'b1;

re<=1'b0;

wr<=1'b0;

Mux1<=1'b1;

Mux2<=2'b0;

Mux3<=1'b0;

Mux5<=1'b1;

MuxAlu<=1'b0;

branch<=1'b0;

pc_sel<=1'b0;

im_select<=1'b1;

pstate<=s0;

end

//*********************************************************************************************************************

4'b0011:begin

alu_op<=4'b0011;

reg_wrt<=1'b1;

re<=1'b0;

wr<=1'b0;

Mux1<=1'b1;

Mux2<=2'b0;

Mux3<=1'b0;

Mux5<=1'b1;

MuxAlu<=1'b0;

branch<=1'b0;

pc_sel<=1'b0;

im_select<=1'b1;

pstate<=s0;

end

//*********************************************************************************************************************

4'b0100:begin

alu_op<=4'b0100;

reg_wrt<=1'b1;

re<=1'b0;

wr<=1'b0;

Mux1<=1'b1;

Mux2<=2'b0;

Mux3<=1'b0;

Mux5<=1'b1;

MuxAlu<=1'b0;

branch<=1'b0;

pc_sel<=1'b0;

im_select<=1'b1;

pstate<=s0;

end

//*********************************************************************************************************************

4'b0101:begin

alu_op<=4'b0101;

reg_wrt<=1'b1;

re<=1'b0;

wr<=1'b0;

Mux1<=1'b1;

Mux2<=2'b0;

Mux3<=1'b0;

Mux5<=1'b1;

MuxAlu<=1'b0;

branch<=1'b0;

pc_sel<=1'b0;

im_select<=1'b1;

pstate<=s0;

end

//*********************************************************************************************************************

4'b0110:begin

alu_op<=4'b0110;

reg_wrt<=1'b1;

re<=1'b0;

wr<=1'b0;

Mux1<=1'b1;

Mux2<=2'b0;

Mux3<=1'b0;

Mux5<=1'b1;

MuxAlu<=1'b0;

branch<=1'b0;

pc_sel<=1'b0;

im_select<=1'b1;

pstate<=s0;

end

//*********************************************************************************************************************

4'b0111:begin

alu_op<=4'b0111;

reg_wrt<=1'b1;

re<=1'b0;

wr<=1'b0;

Mux1<=1'b1;

Mux2<=2'b0;

Mux3<=1'b0;

Mux5<=1'b1;

MuxAlu<=1'b0;

branch<=1'b0;

pc_sel<=1'b0;

im_select<=1'b1;

pstate<=s0;

end

//*********************************************************************************************************************

4'b1000:begin

alu_op<=4'b1000;

reg_wrt<=1'b1;

re<=1'b0;

wr<=1'b0;

Mux1<=1'b1;

Mux2<=2'b0;

Mux3<=1'b0;

Mux5<=1'b1;

MuxAlu<=1'b0;

branch<=1'b0;

pc_sel<=1'b0;

im_select<=1'b0;

pstate<=s0;

end

//*********************************************************************************************************************

4'b1001:begin

alu_op<=4'b1001;

reg_wrt<=1'b1;

re<=1'b0;

wr<=1'b0;

Mux1<=1'b1;

Mux2<=2'b0;

Mux3<=1'b0;

Mux5<=1'b1;

MuxAlu<=1'b0;

branch<=1'b0;

pc_sel<=1'b0;

im_select<=1'b0;

pstate<=s0;

end

//*********************************************************************************************************************

4'b1010:begin

alu_op<=4'b1010;

reg_wrt<=1'b1;

re<=1'b0;

wr<=1'b0;

Mux1<=1'b1;

Mux2<=2'b0;

Mux3<=1'b0;

Mux5<=1'b1;

MuxAlu<=1'b0;

branch<=1'b0;

pc_sel<=1'b0;

im_select<=1'b0;

pstate<=s0;

end   /* DO NOT MODIFY R-FORMAT ENDS HERE */

//*********************************************************************************************************************

4'b1011:begin /*DO NOT MODIFY--I FORMAT STARTS HERE--LOAD*/

alu_op<=4'b0;

reg_wrt<=1'b1;

re<=1'b1;

wr<=1'b0;

Mux1<=1'b0;

Mux2<=2'b01;

Mux3<=1'b1;

Mux5<=1'b1;

MuxAlu<=1'b0;

branch<=1'b0;

pc_sel<=1'b0;

im_select<=1'b1;

pstate<=s0;

end

//********************************************************************************************************************

4'b1100:begin /*DO NOT MODIFY--I FORMAT--STORE*/

alu_op<=4'b0;

reg_wrt<=1'b0;

re<=1'b0;

wr<=1'b1;

Mux1<=1'b1;

Mux2<=2'b01;

Mux3<=1'b1;

Mux5<=1'b1;

MuxAlu<=1'b0;

branch<=1'b0;

pc_sel<=1'b0;

im_select<=1'b1;

pstate<=s0;

end   /* DO NOT MODIFY--I FORMAT ENDS HERE  */

//********************************************************************************************************************

4'b1101:begin /* DO NOT MODIFY -- BEQ  */

alu_op<=4'b0001;

reg_wrt<=1'b0;

re<=1'b0;

wr<=1'b0;

Mux1<=1'b1;

Mux2<=2'b0;

Mux3<=1'b0;

Mux5<=1'b1;

MuxAlu<=1'b0;

branch<=1'b1;

pc_sel<=1'b0;

im_select<=1'b1;

pstate<=s0;

end   /* DO NOT MODIFY -- BEQ */

//*******************************************************************************************************************

4'b1110:begin /* DO NOT MODIFY -- JMP  */

alu_op<=4'b1110;

reg_wrt<=1'b0;

re<=1'b0;

wr<=1'b0;

Mux1<=1'b1;

Mux2<=2'b10;

Mux3<=1'b0;

Mux5<=1'b0;

MuxAlu<=1'b0;

branch<=1'b0;

pc_sel<=1'b0;

im_select<=1'b1;

pstate<=s0;

end   

endcase

end

s2:begin

reg_wrt<=1'b0;

re<=1'b0;

wr<=1'b0;

Mux1<=1'b0;

Mux2<=1'b0;

Mux3<=1'b0;

alu_op<=4'bxxxx;

MuxAlu<=1'b0;

branch<=1'b1;

pc_sel<=1'b0;

im_select<=1'b0;

pstate<=s0;

end

s3:begin

reg_wrt<=1'b1;

re<=1'bx;

wr<=1'b0;

Mux1<=1'b1;

Mux2<=1'b1;

Mux3<=1'b1;

alu_op<=4'bxxxx;

MuxAlu<=1'b0;

branch<=1'b0;

pc_sel<=1'b0;

im_select<=1'b0;

pstate<=s0;

end

endcase

end

endmodule

Risc Top Module

**************************************************************************************

module risc(clk,reset);

input clk,reset;

wire [3:0]opcode;

wire [3:0]alu_op;

wire [2:0] alu_sel;

wire [1:0] opb_sel,data_sel;

wire [15:0] outA;

wire carry,reset,reg_wrt,re,wr,Mux1,Mux2,Mux3,branch,im_wrt,sel1,sel2,sel3;

control control_path(alu_op,opcode,clk,carry,reset,reg_wrt,re,wr,sel1,sel2,sel3,sel5,sel6,branch,pc_sel,im_select);

datapath data_path(alu_op,opcode,clk,carry,sel1,sel2,sel3,sel5,sel6,re,wr,reg_wrt,reset,pc_sel,im_select,branch);

endmodule

Testbench

**************************************************************************************

`timescale 1ns / 1ps

////////////////////////////////////////////////////////////////////////////////

// Company: 

// Engineer:

//

// Create Date:   02:38:30 04/03/2017

// Design Name:   risc

// Module Name:   F:/Season 1/RiscPipeline/JIZ.v

// Project Name:  RiscPipeline

// Target Device:  

// Tool versions:  

// Description: 

//

// Verilog Test Fixture created by ISE for module: risc

//

// Dependencies:

// 

// Revision:

// Revision 0.01 - File Created

// Additional Comments:

// 

////////////////////////////////////////////////////////////////////////////////

module JIZ;

// Inputs

reg clk;

reg reset;

// Instantiate the Unit Under Test (UUT)

risc uut (

.clk(clk), 

.reset(reset)

);

initial begin

// Initialize Inputs

clk = 0;

reset = 0;

// Wait 100 ns for global reset to finish

#40$finish;

        

// Add stimulus here

end

always #1 clk = !clk;

      

endmodule

**************************************************************************************

For more details amigos you can also visit my page

16bit RISC Processor

Here is the Data Path of processor

However if you cannot find image in fine condition you can mail me at 

shashisuman17@aol.com. I will send highest quality Datapath

The schematic block diagram

Here is the processor in action

ISA as per my design- Can be modified too

15 GPRs in Register File
R0 always contains zero. Modify it as you want but not recommended.
Instructions are represented by 2 bytes.
LOAD and STORE moves data to and forth from register to RAM and vice versa

Cheers Guys- If you get in some trouble comment and if you have found some mistakes be kind to inform me. :)

Patch 1.0.0 released - Download
1. JIZ instruction has been added.
    Opcode 1111 if Register has content as zero then it will jump to the given address

If you face any problem with code reply immediately

So Long :)