//////////////////////////////////////////////////////////////////////////////// /// /// Solution to LSU EE 3755 Spring 2002 Homework 1 /// // Assignment: http://www.ee.lsu.edu/ee3755/2002/hw01.pdf //////////////////////////////////////////////////////////////////////////////// /// Problem 1 /// module decode_2_to_4(x0,x1,x2,x3,a); input [1:0] a; output x0, x1, x2, x3; not n0(a0n,a[0]); not n1(a1n,a[1]); and a0(x0,a1n,a0n); and a1(x1,a1n,a[0]); and a2(x2,a[1],a0n); and a3(x3,a[1],a[0]); endmodule //////////////////////////////////////////////////////////////////////////////// /// Problem 2 /// module atoi_implicit(i,s); input [15:0] s; output [7:0] i; assign i[3:0] = s[3:0] + ( s[6] ? 4'd9 : 4'd0 ); assign i[7:4] = s[11:8] + ( s[14] ? 4'd9 : 4'd0 ); endmodule module not_a_good_solution_atoi_implicit(i,s); input [15:0] s; output [7:0] i; parameter ascii_0 = 48; parameter ascii_a = 97; // The code below should work (but not tested) however it requires // more hardware than the first solution. In particular, it does a // magnitude comparison when it's sufficient to test a single bit // of s. It does 8-bit subtractions when only the four least // significant bits are used. assign i[3:0] = s[7:0] >= ascii_a ? s[7:0] - ascii_a + 10 : s[7:0] - ascii_0; assign i[7:4] = s[15:8] >= ascii_a ? s[15:8] - ascii_a + 10 : s[15:8] - ascii_0; endmodule //////////////////////////////////////////////////////////////////////////////// /// Problem 3 /// module atoi_explicit(i,s); input [15:0] s; output [7:0] i; add4 s0(i[3:0],s[3:0],{s[6],2'b0,s[6]}); add4 s1(i[7:4],s[11:8],{s[14],2'b0,s[14]}); endmodule // // Modules for use in Problem 3 // // DO NOT modify these modules. module sub4(d,a,b); input [3:0] a, b; output [3:0] d; assign d = a - b; endmodule module add4(d,a,b); input [3:0] a, b; output [3:0] d; assign d = a + b; endmodule module sub7(d,a,b); input [6:0] a, b; output [6:0] d; assign d = a - b; endmodule module add7(d,a,b); input [6:0] a, b; output [6:0] d; assign d = a + b; endmodule //////////////////////////////////////////////////////////////////////////////// /// Testbenches /// module test_decoder(); parameter stop_on_error = 1; reg [1:0] a; wire x0, x1, x2, x3; reg [3:0] x; decode_2_to_4 your_decoder(x0,x1,x2,x3,a); integer i, err; initial begin err = 0; for(i=0; i<4; i=i+1) begin a = i[1:0]; #1; x = 1 << a; if( {x3,x2,x1,x0} !== x ) begin \$display("FAIL: Demux wrong output for input %d",a); err = err + 1; if( stop_on_error ) \$stop; end end if( !err ) \$write("PASS: "); \$write("Tests completed, "); if( err ) \$display("encountered %d errors.",err); else \$display("no errors found.\n"); \$display("Thank you for using the decode testbench."); end endmodule module test_atoi(); wire [7:0] ie, ii; reg [15:0] s; parameter stop_on_error = 1; parameter ascii_0 = 48; parameter ascii_a = 97; atoi_explicit our_atoi_explicit(ie,s); atoi_implicit our_atoi_implict(ii,s); integer i, err_i, err_e; integer d0, d1; initial begin err_i = 0; err_e = 0; for(i=0; i<256; i=i+1) begin d0 = i & 15; d1 = i >> 4; s[7:0] = d0 < 10 ? d0 + ascii_0 : d0 + ascii_a - 10; s[15:8] = d1 < 10 ? d1 + ascii_0 : d1 + ascii_a - 10; #1; if( ie !== i ) begin \$display("FAIL: Explicit, wrong output, 0x%h (correct) != 0x%h", i,ie); err_e = err_e + 1; if( stop_on_error ) \$stop; end if( ii !== i ) begin \$display("FAIL: Implicit, wrong output, 0x%h (correct) != 0x%h", i,ii); err_i = err_i + 1; if( stop_on_error ) \$stop; end end if( !err_i ) \$write("PASS: "); \$write("Implicit tests completed, "); if( err_i ) \$display("encountered %d errors.",err_i); else \$display("no errors found.\n"); if( !err_e ) \$write("PASS: "); \$write("Explicit tests completed, "); if( err_e ) \$display("encountered %d errors.",err_e); else \$display("no errors found.\n"); end endmodule