First cut at timer

[fpgaboy.git] / Interrupt.v

`define ADDR_IF 16'hFF0F
`define ADDR_IE 16'hFFFF

module Interrupt(
	input clk,
	input rd,
	input wr,
	input [15:0] addr,
	inout [7:0] data,
	input vblank,
	input lcdc,
	input tovf,
	input serial,
	input buttons,
	output master,
	output [7:0] jaddr);

	wire [7:0] iflag = {3'b0,buttons,serial,tovf,lcdc,vblank};
	reg [7:0] imask = 16'hFFFF;
	reg [7:0] ihold = 0;
	wire [7:0] imasked = ihold & imask;

	assign data = rd ?
	                 (addr == `ADDR_IF) ? ihold :
	                 (addr == `ADDR_IE) ? imask :
	                 8'bzzzzzzzz :
		      8'bzzzzzzzz;

	assign master = (imasked) != 0;

	assign jaddr = imasked[0] ? 8'h40 :
		       imasked[1] ? 8'h48 :
		       imasked[2] ? 8'h50 :
		       imasked[3] ? 8'h58 :
		       imasked[4] ? 8'h60 : 8'h00;

	always @ (negedge clk)
	begin
		if (wr) begin
			case(addr)
			`ADDR_IF : ihold <= iflag | data;
			`ADDR_IE : imask <= data;
			endcase
			
		end
		else
			ihold <= ihold | iflag;
	end

endmodule