PC.v

/*module ProgramCounter(PC, PC4, in, PS, clock, reset);
	input [63:0]in;
	input [1:0]PS; // Program counter function Select bits
/*
	PS |
	---+----------------
	00 | PC <- PC
	01 | PC <- PC + 4
	10 | PC <- in
	11 | PC <- PC + 4 +in*4
	*/
/*	input clock, reset;
	output [63:0]PC;
	output [63:0]PC4;
	
	wire [63:0] PC_in; // input to program counter / output from mux
	wire [63:0] AdderOut; // output of offeset adder
	wire load_PC;
	assign load_PC = 1'b1;
	assign PC4 = PC + 4; // +4 adder
	assign AdderOut = PC4 + {in[61:0], 2'b00};
	Mux4to1Nbit PC_Mux (PC_in, PS, PC, PC4, in, AdderOut);
	defparam PC_Mux.N = 64;
	RegisterNbit PC_Reg (PC, PC_in, load_PC, reset, clock);
	defparam PC_Reg.N = 64;
endmodule


module Mux4to1Nbit (F, S, I00, I01, I02, I03);
	parameter N = 4;
	input [1:0] S;
	input [N-1:0] I00, I01, I02, I03;
	output reg [N-1:0] F;
	always @(*) begin
    case (S)
        2'b00: F <= I00;
        2'b01: F <= I01;
        2'b10: F <= I02;
        2'b11: F <= I03;
    endcase 
end
endmodule
*/


module ProgramCounter(PC, PC_in, in, PS, clock,reset);
	input [1:0] PS; 
	input [63:0]in;
	input clock, reset;
	output reg [63:0] PC;
	output [63:0] PC_in;
	
	wire [63:0] PC4 = PC + 64'd4;
	wire load = PS[0] | PS[1];
	
	assign PC_in = PC4;

always @(posedge clock or posedge reset) begin
	if (reset) begin
		PC = 64'd0;
	end
	
	else if (load) begin
	case(PS)
	// Program Counter is incremented by four	
		2'b01: PC = PC4;
	// Program Counter is incremented by a specified value
		2'b10: PC = in;
	// Program Counter is increment by four  plus a specified value times 4
		2'b11: PC = PC4 + in*64'd4;	
	endcase
	end
	
	else begin
	// Program Counter is constant
		PC = PC;
	end
end 

endmodule