Verilog Descriptions of Digital Systems

Design Flow

Verilog Lab #3

 Design a serial adder circuit using Verilog.  The circuit should add two 8-bit numbers, A and B.  The result should be stored back into the A register.  Use the diagram below to guide you.   Hint:  Write one module to describe the datapath and a second module to describe the control.  Annotate your simvision trace output to demonstrate that the adder works correctly.  Demonstrate by adding $45 to $10 in your testbench.

 

Serial Adder Data Path

pinB

Adder/Subtractor

// 4-bit full-adder (behavioral)

module fa(sum, co, a, b, ci) ; input [3:0] a, b ; input ci ; output [3:0] sum ; output co ;

assign {co, sum} = a + (ci ? ~b : b) + ci ;

endmodule

Serial Adder Control Logic

T0: if (!start) goto T0T1: if (start) goto T1T2: if (clrA) A <= 0, B <= pinB, C <= 0T3: A <= shr(A), B <= shr(B)T4: A <= shr(A), B <= shr(B)T5: A <= shr(A), B <= shr(B)T6: A <= shr(A), B <= shr(B), goto T0

pinB

Controller and Datapath Modules

module serial_adder_datapath(sum, sout, pinB, ctl, reset, clk) ; output [7:0] sum ; output sout ; input sinB ; input [ ] ctl ; input reset, clk ;

endmodule module serial_adder_control(ctl, busy, start, clrA, reset, inv_clk) ; output [ ] ctl ; output busy ; input reset, start, inv_clk ;

endmodule

pinB

Three Techniques for Building Control Units

1. Classical FSM2. One-Hot3. Decode a Counter

T0: if (!start) goto T0

T1: if (start) goto T1

T2: if (clrA) A <= 0, B <= pinB, C <= 0

T3: A <= shr(A), B <= shr(B)

T4: A <= shr(A), B <= shr(B)

T5: A <= shr(A), B <= shr(B)

T6: A <= shr(A), B <= shr(B), goto T0

Binary Multiplication

Binary Multiplier

ASM Chart

Numerical Example

Serial Multiplier (Verilog)// multiplier

module multiplier(S, clk, clr, Bin, Qin, C, A, Q, P) ; input S, clk, clr ; input [4:0] Bin, Qin ; output C ; output [4:0] A, Q ; output [2:0] P ;

// system registers

reg C ; reg [4:0] A, Q, B ; reg [2:0] P ; reg [1:0] pstate, nstate ;

parameter T0 = 2'b00, T1= 2'b01, T2 = 2'b10, T3 = 2'b11 ;

// combinational circuit

wire Z ; assign Z = ~|P ;

// state register process for controller

always @(negedge clk or negedge clr) begin if (~clr) pstate <= T0 ; else pstate <= nstate ; end

Serial Multiplier (Continued)// state transition process for controller

always @(S or Z or pstate) begin case (pstate) T0: if (S) nstate = T1; else nstate = T0 ; T1: nstate = T2 ; T2: nstate = T3 ; T3: if (Z) nstate = T0; else nstate = T2 ; endcase end

// register transfer operations

always @(posedge clk) begin case (pstate) T0: B <= Bin ; T1: begin A <= 0 ; C <= 1 ; P <= 5 ; Q <= Qin ; end T2: begin P <= P - 1 ; if (Q[0]) {C,A} <= A + B ; end T3: begin C <= 0 ; A <= {C, A[4:1]} ; Q <= {A[0], Q{4:1]} ; end endcase endendmodule

Serial Multiplier (Testbench)

// multiplier testbench

module multiplier_tb; reg S, clk, clr ; reg [4:0] Bin, Qin ; wire C ; wire [4:0] A, Q ; wire [2:0] P ;

// instantiate multiplier

multiplier uut(S, clk, clr, Bin, Qin, C, A, Q, P);

// generate test vectors

initial begin #0 begin S = 0; clk = 0; clr = 0 ; end #5 begin S = 1; clr = 1; Bin = 5'b10111 ; Qin = 5'b10011 ; #15 begin S = 0 ; end end

Serial Multiplier (Testbench, continued)

// create dumpfile and generate clock

initial begin $dumpfile("./multiplier.dmp") ; $dumpflush ; $dumpvars(2, multiplier_tb) ; repeat (26) #5 clk = ~clk ; end endmodule