IP

[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,
	input ack,
	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 = 8'b0;
	wire [7:0] imasked = ihold & imask;
	
	reg rdlatch = 0;
	reg [15:0] addrlatch = 0;

	assign data = rdlatch ?
	                 (addrlatch == `ADDR_IF) ? ihold :
	                 (addrlatch == `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 @(posedge clk)
	begin
		if (wr && (addr == `ADDR_IF || addr == `ADDR_IE)) begin
			case(addr)
			`ADDR_IF : ihold <= iflag | data;
			`ADDR_IE : begin imask <= data; ihold <= ihold | iflag; end
			endcase
			
		end else if (ack)
			ihold <= ihold &
				(imasked[0] ? 8'b11111110 :
				 imasked[1] ? 8'b11111101 :
				 imasked[2] ? 8'b11111011 :
				 imasked[3] ? 8'b11110111 :
				 imasked[4] ? 8'b11101111 :
				 8'b11111111);
		else
			ihold <= ihold | iflag;
		rdlatch <= rd;
		addrlatch <= addr;
	end

endmodule