Verilog Descriptions of Digital Systems

1. Verilog Descriptions of Digital Systems

2. Design Flow

3. 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.

4. Serial Adder Data Path pinB

5. 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

6. Serial Adder Control Logic pinB 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

7. Controller and Datapath Modules pinB 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

8. Three Techniques for Building Control Units • Classical FSM • One-Hot • 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

9. Binary Multiplication

10. Binary Multiplier

11. ASM Chart

12. Numerical Example

13. 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

14. // 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 end endmodule Serial Multiplier (Continued)

15. 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

16. 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