Drop the idiotic 6-bit RGB from the display unit; add reverse video

Output 3-bit RGB from the display unit since that's what we're
actually generating.  Add a reverse video option on SW7.

1 files changed, 17 insertions, 29 deletions

diff --git a/display.v b/display.v
index a9c688f..d1fd869 100644
--- a/display.v
+++ b/display.v
@@ -1,6 +1,7 @@
 module display (
 		clk,
 		width,
+		reverse,
 		reveal,
 		a,
 		d,
@@ -12,13 +13,14 @@ module display (
 		);
    input         clk;
    input         width;
+   input 	 reverse;
    input 	 reveal;
    output [10:0] a;
    input [7:0] 	 d;
    output [10:0] ga;
    input [7:0] 	 gd;
-   output [5:0]  rgb;
-   reg [5:0] 	 rgb;
+   output [2:0]  rgb;
+   reg [2:0] 	 rgb;
    output 	 vsync;
    reg 		 vsync;
    output 	 hsync;
@@ -46,12 +48,6 @@ module display (
 //             ---------
 //             449 lines
 //
-// The DAC has an 8-cycle latency, plus we read each character 8
-// cycles beforehand.  Thus we reduce the horizontal front porch
-// by 16 and add it to the back porch.  The front and back porch
-// values can be adjusted to justify the positioning of the picture
-// on the screen.
-// 
 // In this implementation we start timing with the display area in both
 // cases, *except* that we prefetch by one character, and therefore start
 // 1 character shy of the actual start of display.
@@ -85,6 +81,7 @@ module display (
    wire [10:0] 	 a80u;		// Character row assuming 80 columns (up 1 line)
    reg [5:0] 	 scan_counter;	// Counter of total scans (for flashing et al)
    reg [7:0] 	 pixrow;	// One character worth of pixels
+   reg 		 prefetch;	// True for the prefetch character position
 
    // For the current text line
    reg [2:0] 	 curfg;		// Foreground RGB
@@ -148,33 +145,21 @@ module display (
 
    // Flashing
    wire 	 flash_blank = scan_counter[5];
-   wire 	 iflash = inverse & ~flash_blank;
+   wire 	 iflash = (inverse & ~flash_blank)^reverse;
 
    // Synchronous logic
 
    always @(posedge clk)
      begin
-	if ( xvideo & yvideo )
+	// The x[9:4] means ignore the first character prefetch.  We really
+	// should realign the counters, here.
+	if ( xvideo & yvideo & ~prefetch )
 	  if ( pixrow[7] & ~(do_flsh & flash_blank) & ~(do_hide & ~reveal) )
-	    begin
-	       rgb[5] <= fg[2] ^ iflash;
-	       rgb[4] <= fg[2] ^ iflash;
-	       rgb[3] <= fg[1] ^ iflash;
-	       rgb[2] <= fg[1] ^ iflash;
-	       rgb[1] <= fg[0] ^ iflash;
-	       rgb[0] <= fg[0] ^ iflash;
-	    end
+	    rgb <= fg ^ {3{iflash}};
 	  else
-	    begin
-	       rgb[5] <= bg[2] ^ iflash;
-	       rgb[4] <= bg[2] ^ iflash;
-	       rgb[3] <= bg[1] ^ iflash;
-	       rgb[2] <= bg[1] ^ iflash;
-	       rgb[1] <= bg[0] ^ iflash;
-	       rgb[0] <= bg[0] ^ iflash;
-	    end
+	    rgb <= bg ^ {3{iflash}};
 	else
-	  rgb <= 6'b0;
+	  rgb <= 3'b0;		// Blank
 
 	// Sync pulses
 	vsync <= ( y >= y_sync && y < y_front ) ^ ~vsync_polarity;
@@ -207,9 +192,8 @@ module display (
 		    // Load a new pixel row?
 		    if ( xvideo )
 		      begin
-
 			 // Attribute engine for current row
-			 
+
 			 if ( thischar[6:5] == 2'b00 )
 			   begin
 			      // Control character
@@ -356,6 +340,9 @@ module display (
 			   end // if ( wasdble ? (wasgraph & thatchar[5]) : (isgraph & thischar[5]) )
 			 else if ( (somechar[6:5] != 2'b00) | (wasdble ? wasgrel : isgrel) )
 			   pixrow <= gd; // Input from character ROM
+
+			 // This is no longer a prefetch character...
+			 prefetch <= 1'b0;
 		      end // if ( xvideo )
 		    inverse <= somechar[7];
 		 end // case: 3'b111
@@ -367,6 +354,7 @@ module display (
 	  begin
 	     x <= 0;
 	     pixrow <= 8'b0;	// Read-ahead spot is blank
+	     prefetch <= 1'b1;	// Prefetch character
 	     inverse <= 0;	// Not inverse video
 	     curfg <= 3'b111;	// Default fg is white
 	     curbg <= 3'b000;	// Default bg is black