Warp-SE/cpld/CS.v
2023-03-31 06:14:47 -04:00

60 lines
2.2 KiB
Verilog

module CS(
/* MC68HC000 interface */
input [23:08] A, input CLK, input nRES, input nWE,
/* AS cycle detection */
input BACT,
/* Device select outputs */
output IOCS, output IOPWCS, output IACS, output ROMCS, output RAMCS, output SndRAMCSWR);
/* Overlay control */
reg nOverlay = 0; wire Overlay = !nOverlay;
reg ODCSr;
always @(posedge CLK) begin
ODCSr <= (A[23:20]==4'h4) && BACT;
if (!BACT) begin
if (!nRES) nOverlay <= 0;
else if (ODCSr) nOverlay <= 1;
end
end
/* Select signals - FSB domain */
assign RAMCS = (A[23:22]==2'b00) && !Overlay; // 000000-3FFFFF when overlay disabled
wire VidRAMCSWR64k = RAMCS && (A[21:20]==2'h3) && (A[19:16]==4'hF) && ~nWE; // 3F0000-3FFFFF / 7F0000-7FFFFF
wire VidRAMCSWR = VidRAMCSWR64k && (
(A[15:12]==4'h2) || // 1792 bytes RAM, 2304 bytes video
(A[15:12]==4'h3) || // 4096 bytes video
(A[15:12]==4'h4) || // 4096 bytes video
(A[15:12]==4'h5) || // 4096 bytes video
(A[15:12]==4'h6) || // 4096 bytes video
(A[15:12]==4'h7) || // 3200 bytes video, 896 bytes RAM,
(A[15:12]==4'hA) || // 256 bytes RAM, 768 bytes sound, 768 bytes RAM, 2304 bytes video
(A[15:12]==4'hB) || // 4096 bytes video
(A[15:12]==4'hC) || // 4096 bytes video
(A[15:12]==4'hD) || // 4096 bytes video
(A[15:12]==4'hE) || // 4096 bytes video
(A[15:12]==4'hF)); // 3200 bytes video, 128 bytes RAM (system error space), 768 bytes sound
assign SndRAMCSWR = VidRAMCSWR64k && (
((A[15:12]==4'hF) && ((A[11:8]==4'hD) || (A[11:8]==4'hE) || (A[11:8]==4'hF))) ||
((A[15:12]==4'hA) && ((A[11:8]==4'h1) || (A[11:8]==4'h2) || (A[11:8]==4'h3))));
assign ROMCS = ((A[23:20]==4'h0) && Overlay) || (A[23:20]==4'h4);
/* Select signals - IOB domain */
assign IACS = (A[23:08]==16'hFFFF); // IACK
assign IOCS = ((A[23:20]==4'h4) && Overlay) || // ROM once
(A[23:20]==4'h5) || // SCSI
(A[23:20]==4'h6) || // empty
(A[23:20]==4'h7) || // empty
(A[23:20]==4'h8) || // empty
(A[23:20]==4'h9) || // SCC read/reset
(A[23:20]==4'hA) || // empty
(A[23:20]==4'hB) || // SCC write
(A[23:20]==4'hC) || // empty / fast ROM
(A[23:20]==4'hD) || // IWM
(A[23:20]==4'hE) || // VIA
(A[23:20]==4'hF) || // IACK
VidRAMCSWR;
assign IOPWCS = RAMCS && !nWE;
endmodule