Verilog HDL:Digital Design and Modeling Chapter 10 Tasks and - PDF document

Chapter 10 Tasks and Functions 1 Verilog HDL:Digital Design and Modeling Chapter 10 Tasks and Functions

Chapter 10 Tasks and Functions 2 Page 584 //module to illustrate a task module task_arith_log; reg [7:0] a, b, c; reg [7:0] z1, z2, z3, z4; initial begin a=8'b0000_1111; b=8'b0011_1100; c=8'b0101_0101; calc (a, b, c, z1, z2, z3, z4); //invoke task a=8'b1111_1111; b=8'b0000_1100; c=8'b1011_1101; calc (a, b, c, z1, z2, z3, z4); //invoke task a=8'b0011_1100; b=8'b0001_1101; c=8'b1010_0101; calc (a, b, c, z1, z2, z3, z4); //invoke task a=8'b1100_1001; b=8'b1011_1101; c=8'b0111_0111; calc (a, b, c, z1, z2, z3, z4); //invoke task end task calc; input [7:0] a, b, c; output [7:0] z1, z2, z3, z4; begin z1 = (a + b) & (c); z2 = (a + b) | (c); z3 = (a & b) + (c); z4 = (a | b) + (c); $display ("a=%b, b=%b, c=%b, z1=%b, z2=%b, z3=%b, z4=%b", a, b, c, z1, z2, z3, z4); end endtask endmodule Figure 10.1 Module for the task of Example 10.1.

Chapter 10 Tasks and Functions 3 Page 585 a=00001111, b=00111100, c=01010101, z1=01000001, z2=01011111, z3=01100001, z4=10010100 a=11111111, b=00001100, c=10111101, z1=00001001, z2=10111111, z3=11001001, z4=10111100 a=00111100, b=00011101, c=10100101, z1=00000001, z2=11111101, z3=11000001, z4=11100010 a=11001001, b=10111101, c=01110111, z1=00000110, z2=11110111, z3=00000000, z4=01110100 Figure 10.2 Outputs for the task module of Figure 10.2.

Chapter 10 Tasks and Functions 4 Page 586 //module to illustrate a task for logical operations module task_logical; reg [7:0] a, b; reg [7:0] a_and_b, a_nand_b, a_or_b, a_nor_b, a_xor_b, a_xnor_b; initial begin a=8'b1010_1010; b=8'b1100_1100; logical (a, b, a_and_b, a_nand_b, a_or_b, a_nor_b, a_xor_b, a_xnor_b); //invoke the task a=8'b1110_0111; b=8'b1110_0111; logical (a, b, a_and_b, a_nand_b, a_or_b, a_nor_b, a_xor_b, a_xnor_b); //invoke the task a=8'b0000_0111; b=8'b0000_0111; logical (a, b, a_and_b, a_nand_b, a_or_b, a_nor_b, a_xor_b, a_xnor_b); //invoke the task a=8'b0101_0101; b=8'b1010_1010; logical (a, b, a_and_b, a_nand_b, a_or_b, a_nor_b, a_xor_b, a_xnor_b); //invoke the task end task logical; input [7:0] a, b; output [7:0] a_and_b, a_nand_b, a_or_b, a_nor_b, a_xor_b, a_xnor_b; begin a_and_b = a & b; a_nand_b = ~(a & b); a_or_b = a | b; a_nor_b = ~(a | b); a_xor_b = a ^ b; a_xnor_b = ~(a ^ b); $display ("a=%b, b=%b, a_and_b=%b, a_nand_b=%b, a_or_b=%b, a_nor_b=%b, a_xor_b=%b, a_xnor_b=%b", a, b, a_and_b, a_nand_b, a_or_b, a_nor_b, a_xor_b, a_xnor_b); end endtask endmodule Figure 10.5 Module for the task of Example 10.2.

Chapter 10 Tasks and Functions 5 Page 587 a=10101010, b=11001100, a_and_b=10001000, a_nand_b=01110111, a_or_b=11101110, a_nor_b=00010001, a_xor_b=01100110, a_xnor_b=10011001 a=11100111, b=11100111, a_and_b=11100111, a_nand_b=00011000, a_or_b=11100111, a_nor_b=00011000, a_xor_b=00000000, a_xnor_b=11111111 a=00000111, b=00000111, a_and_b=00000111, a_nand_b=11111000, a_or_b=00000111, a_nor_b=11111000, a_xor_b=00000000, a_xnor_b=11111111 a=01010101, b=10101010, a_and_b=00000000, a_nand_b=11111111, a_or_b=11111111, a_nor_b=00000000, a_xor_b=11111111, a_xnor_b=00000000 Figure 10.6 Outputs for the task module of Figure 10.5.

Chapter 10 Tasks and Functions 6 Page 588 //module to illustrate the use of a task module task1_adder4; integer a, b, cin, sum; initial begin a=2; b=5; cin=0; add (a, b, cin, sum); //invoke the task a=3; b=2; cin=1; add (a, b, cin, sum); //invoke the task a=4; b=6; cin=1; add (a, b, cin, sum); //invoke the task a=14; b=63; cin=1; add (a, b, cin, sum); //invoke the task a=150; b=225; cin=0; add (a, b, cin, sum); //invoke the task end task add; input a; input b; input cin; output sum; integer a, b, cin, sum; begin sum = a + b + cin; $display ("a=%d, b=%d, cin=%d, sum=%d", a, b, cin, sum); end endtask endmodule Figure 10.8 Module for the task of Example 10.3. a = 2, b = 5, cin = 0, sum = 7 a = 3, b = 2, cin = 1, sum = 6 a = 4, b = 6, cin = 1, sum = 11 a = 14, b = 63, cin = 1, sum = 78 a = 150, b = 225, cin = 0, sum = 375 Figure 10.9 Outputs for the task module of Figure 10.8.

Chapter 10 Tasks and Functions 7 Page 590 //module to illustrate a function module fctn_parity; reg [15:0] addr; reg parity; initial begin parity = calc_parity (16’b1111_0000_1111_0000); if (parity ==1) $display ("parity is even"); else $display ("parity is odd"); parity = calc_parity (16’b1111_0000_1111_0001); if (parity ==1) $display ("parity is even"); else $display ("parity is odd"); end function calc_parity; input [15:0] address; begin calc_parity = ^address; end endfunction endmodule Figure 10.11 Module for the function of Example 10.4. parity is even parity is odd Figure 10.12 Outputs for the function module of Figure 10.11.

Chapter 10 Tasks and Functions 8 Page 592 //module to illustrate a function module fctn_count1s; reg [3:0] count; //invoke the function initial begin count = count1s (8'b1100_0011); $display ("number of 1s = %d", count); count = count1s (8'b1101_0011); $display ("number of 1s = %d", count); count = count1s (8'b1111_1011); $display ("number of 1s = %d", count); count = count1s (8'b1010_1010); $display ("number of 1s = %d", count); count = count1s (8'b0000_0000); $display ("number of 1s = %d", count); count = count1s (8'b0000_0010); $display ("number of 1s = %d", count); count = count1s (8'b1111_1111); $display ("number of 1s = %d", count); count = count1s (8'b0110_0100); $display ("number of 1s = %d", count); end //continue on next page Figure 10.13 Module for a function to count the number of 1s in a word.

Chapter 10 Tasks and Functions 9 function [3:0] count1s; input [7:0] reg_a; reg [3:0] cnt; begin cnt = 0; while (reg_a) begin cnt = cnt + reg_a[0]; reg_a = reg_a >> 1; end count1s = cnt; end endfunction endmodule Figure 10.13 (Continued) number of 1s = 4 number of 1s = 5 number of 1s = 7 number of 1s = 4 number of 1s = 0 number of 1s = 1 number of 1s = 8 number of 1s = 3 Figure 10.14 Outputs for a function to count the number of 1s in a word. Page 594 //module for a full adder using a function module fctn_full_add; reg a, b, cin; reg [1:0] sum; initial begin sum = full_add (1'b0, 1'b0, 1'b0); //invoke the function $display ("abcin=000, cout, sum = %b", sum); sum = full_add (1'b0, 1'b0, 1'b1); $display ("abcin=001, cout, sum = %b", sum); //continued on next page Figure 10.16 Module for the full adder function of Example 10.6.

Chapter 10 Tasks and Functions 10 sum = full_add (1'b0, 1'b1, 1'b0); $display ("abcin=010, cout, sum = %b", sum); sum = full_add (1'b0, 1'b1, 1'b1); $display ("abcin=011, cout, sum = %b", sum); sum = full_add (1'b1, 1'b0, 1'b0); $display ("abcin=100, cout, sum = %b", sum); sum = full_add (1'b1, 1'b0, 1'b1); $display ("abcin=101, cout, sum = %b", sum); sum = full_add (1'b1, 1'b1, 1'b0); $display ("abcin=110, cout, sum = %b", sum); sum = full_add (1'b1, 1'b1, 1'b1); $display ("abcin=111, cout, sum = %b", sum); end function [2:0] full_add; input a, b, cin; reg [1:0] sum; begin case ({a,b,cin}) 3'b000: sum = 2'b00; 3'b001: sum = 2'b01; 3'b010: sum = 2'b01; 3'b011: sum = 2'b10; 3'b100: sum = 2'b01; 3'b101: sum = 2'b10; 3'b110: sum = 2'b10; 3'b111: sum = 2'b11; default :sum = 2'bxx; endcase full_add = sum; end endfunction endmodule Figure 10.16 (Continued)

Chapter 10 Tasks and Functions 11 Page 596 abcin=000, cout, sum = 00 abcin=001, cout, sum = 01 abcin=010, cout, sum = 01 abcin=011, cout, sum = 10 abcin=100, cout, sum = 01 abcin=101, cout, sum = 10 abcin=110, cout, sum = 10 abcin=111, cout, sum = 11 Figure 10.17 Outputs for the full adder function module of Figure 10.16.

Chapter 10 Tasks and Functions 12 Page 596 //module for a shifter using a function module fctn_shifter; reg [7:0] left_word, right_word; reg ctrl; initial begin left_word = shift (8'b1010_1010, 1'b0);//invoke function $display ("word = %b", left_word); right_word = shift (8'b1100_0011, 1'b1); $display ("word = %b", right_word); left_word = shift (8'b0000_1111, 1'b0); $display ("word = %b", left_word); right_word = shift (8'b0000_1111, 1'b1); $display ("word = %b", right_word); left_word = shift (8'b0010_0000, 1'b0); $display ("word = %b", left_word); right_word = shift (8'b0010_0000, 1'b1); $display ("word = %b", right_word); end function [7:0] shift; input [7:0] word; input ctrl; begin shift = (ctrl == 1'b0) ? (word << 1) : (word >> 1); end endfunction endmodule Figure 10.18 Module for a function to shift a word left or right 1 bit position. Page 597 word = 01010100 word = 01100001 word = 00011110 word = 00000111 word = 01000000 word = 00010000 Figure 10.19 Outputs for the shift function module of Figure 10.18.