First cut at timer

[fpgaboy.git] / Interrupt.v

diff --git a/Interrupt.v b/Interrupt.v
new file mode 100644 (file)
index 0000000..4e3d17d
--- /dev/null
+++ b/Interrupt.v
@@ -0,0 +1,50 @@
+`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