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Improved overlay latching

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This commit is contained in:
Zane Kaminski 2023-03-31 06:14:47 -04:00
parent 50451da0a5
commit 64acc12a9d
1 changed files with 10 additions and 9 deletions
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19
cpld/CS.v
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@ -7,12 +7,14 @@ module CS(
output IOCS, output IOPWCS, output IACS, output ROMCS, output RAMCS, output SndRAMCSWR);
/* Overlay control */
reg nOverlay = 0;
wire Overlay = ~nOverlay;
wire ODCS = (A[23:20]==4'h4); // Disable overlay
always @(posedge CLK, negedge nRES) begin
if (!nRES) nOverlay <= 0;
else if (BACT && ODCS) nOverlay <= 1;
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 */
@ -35,12 +37,11 @@ module CS(
((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);
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
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