[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