coin_counter.v

Systemverilog 编写的贩卖机代码

module coin_counter (
		empty, clk, dimes, dime_out, load, 
		nickels, nickel_out,  two_dime_out
);

    output empty;
    input clk;
    input [7:0] nickels, dimes;
    input dime_out;
    input nickel_out;
    input two_dime_out;
    input load;

    reg [7:0] nickel_count, dime_count;

    wire empty = !{nickel_count,dime_count};

    always @(negedge clk)
	begin
	if ( load == 1)
		begin : load_block
			nickel_count = nickels;	
			dime_count = dimes;
		end
	else if ( nickel_out == 1 && dime_out == 0 && two_dime_out == 0)
		begin : one_nickel_block
			if (nickel_count != 0)
				nickel_count = sub1(nickel_count);
			else
				$display("** use exact change");
		end

	else if ( nickel_out == 0 && dime_out == 1 && two_dime_out == 0)
	begin : one_dime_block
			if (dime_count != 0)
				dime_count = sub1(dime_count);
			else
				if (nickel_count != 0)
					nickel_count = sub2(nickel_count);
				else
					$display("** use exact change");
		end
	else if ( nickel_out == 0 && dime_out == 0 && two_dime_out == 1)
		begin : two_dime_block
			if (dime_count != 0)
				dime_count = sub2(dime_count);
			else
				if (nickel_count != 0)
					nickel_count = sub4(nickel_count);
				else
					$display("** use exact change");
		end
 	end	
function [7:0] sub1;
	input [7:0] a;
	sub1 = a - 1;
endfunction
			
function [7:0] sub2;
	input [7:0] a;
	sub2 = a - 2;
endfunction

function [7:0] sub4;
	input [7:0] a;
	sub4 = a - 4;
endfunction

endmodule