It works now... mostly :) SRAM problem resolved by pulling up WE# earlier.

1 files changed, 38 insertions, 46 deletions

diff --git a/display.v b/display.v
index 74526b7..6dca8a7 100644
--- a/display.v
+++ b/display.v
@@ -1,6 +1,7 @@
 module display (
 		clk,
 		width,
+		reveal,
 		a,
 		d,
 		ga,
@@ -11,6 +12,7 @@ module display (
 		);
    input         clk;
    input         width;
+   input 	 reveal;
    output [10:0] a;
    input [7:0] 	 d;
    output [10:0] ga;
@@ -29,18 +31,26 @@ module display (
 // is far, far less than the margin of error in real systems.
 //
 // This gives us the following timings:
+//
 // Horizontal:  96 pixels (12 char) sync
 //              40 pixels ( 5 char) back porch/border
 //             640 pixels (80 char) graphics
 //              24 pixels ( 3 char) front porch
+//             ----------
+//             800 pixels
+//  
 // Vertical:     2 lines sync
 //	        41 lines back porch/border
 //	       384 lines graphics (24 rows @ 16 pixels)
 //              22 lines front porch
+//             ---------
+//             449 lines
 //
 // The DAC has an 8-cycle latency, plus we read each character 8
-// cycles beforehand.  Thus we reduce the front porch
-// by 16 and add it to the back porch.
+// 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
@@ -55,14 +65,14 @@ module display (
 // and +vsync, meaning hsync is active low and vsync is active high.
 
    parameter 	 x_blank = 640+8;
-   parameter 	 x_sync = x_blank+48;
+   parameter 	 x_sync = x_blank+32;
    parameter 	 x_front = x_sync+96;
-   parameter 	 x_max = x_front+8;
+   parameter 	 x_max = 800;
 
    parameter 	 y_blank = 384;
-   parameter 	 y_sync = y_blank+22;
+   parameter 	 y_sync = y_blank+30;
    parameter 	 y_front = y_sync+2;
-   parameter 	 y_max = y_front+41;
+   parameter 	 y_max = 449;
 
    parameter 	 hsync_polarity = 1'b0; // -hsync
    parameter 	 vsync_polarity = 1'b1;	// +vsync
@@ -77,15 +87,16 @@ module display (
    reg 		 inverse;	// Inverse video
    reg 		 isgraph;	// Graphic mode?
    reg 		 isgsep;	// Separated graphics?
+   reg 		 isgrel;	// Hold graphics?
+   reg 		 isdble;	// Double height?
    reg 		 isflsh;	// Flashing?
+   reg 		 ishide;	// Hidden
    reg [7:0] 	 thischar;	// Character code currently processing
    wire [3:0] 	 xmiddle;	// Used in address calculation
    wire [3:0] 	 ymiddle;	// Used in address calculation
    wire 	 xvideo;	// Non-blanked in the x direction
    wire 	 yvideo;	// Non-blanked in the y direction
-
-   // Combinatorial logic
-
+   
    // Address mapping for 80 characters; for 40 characters
    // we shift this left by 1
    assign 	 a80[3:0] = x[6:3];
@@ -114,7 +125,7 @@ module display (
    always @(posedge clk)
      begin
 	if ( xvideo & yvideo )
-	  if ( pixrow[7] & ~(isflsh & flash_blank) )
+	  if ( pixrow[7] & ~(isflsh & flash_blank) & ~(ishide & ~reveal) )
 	    begin
 	       rgb[5] <= fg[2] ^ iflash;
 	       rgb[4] <= fg[2] ^ iflash;
@@ -139,9 +150,11 @@ module display (
 	vsync <= ( y >= y_sync && y < y_front ) ^ ~vsync_polarity;
 	hsync <= ( x >= x_sync && x < x_front ) ^ ~hsync_polarity;
 
-	// Shift register; may be overridden by the below
+	// Rotating shift register; may be overridden by the below
+	// The rotation is so that if we're in GHOL mode we already
+	// have the reserved value
 	if ( width | x[0] )
-	  pixrow <= { pixrow[6:0], 1'bx };
+	  pixrow <= { pixrow[6:0], pixrow[7] };
 	
 	// This code is run 8 times per character; regardless of width
 	if ( width | ~x[3] )
@@ -167,6 +180,12 @@ module display (
 				     fg <= thischar[2:0];
 				     isgraph <= thischar[4];
 				  end
+				5'b0110x:
+				  isdble <= thischar[0];
+				5'b11000:
+				  ishide <= 1'b1;
+				5'b1111x:
+				  isgrel <= thischar[0];
 				5'b0100x:
 				  isflsh <= ~thischar[0];
 				5'b11001:
@@ -185,11 +204,11 @@ module display (
 				  end
 			      endcase // casex( thischar[4:0] )
 			   end // if ( thischar[6:5] == 2'b00 )
-
+			 
 			 if ( isgraph & thischar[5] )
 			   begin
 			      // Generate graphical character
-			      case ( y[3:0] )
+			      case ( ga[3:0] )
 				4'h0, 4'h1, 4'h2, 4'h3:
 				  begin
 				     pixrow[7] <= thischar[0];
@@ -256,9 +275,9 @@ module display (
 				     pixrow[1] <= thischar[6] & ~isgsep;
 				     pixrow[0] <= thischar[6] & ~isgsep;
 				  end
-			      endcase // case( y[3:0] )
+			      endcase // case( ga[3:0] )
 			   end // if ( isgraph & thischar[5] )
-			 else
+			 else if ( (thischar[6:5] != 2'b00) | isgrel )
 			   pixrow <= gd; // Input from character ROM
 		      end // if ( xvideo )
 		    inverse <= thischar[7];
@@ -276,6 +295,9 @@ module display (
 	     inverse <= 0;	// Not inverse video
 	     isflsh <= 0;	// Not flashing
 	     isgsep <= 0;	// Not separated
+	     isdble <= 0;	// Not double
+	     isgrel <= 1;	// Release graphics
+	     ishide <= 0;	// Not hidden
 	     pixrow <= 8'b0;	// Read-ahead spot is blank
 	     if ( y == y_max-1 )
 	       begin
@@ -289,34 +311,4 @@ module display (
 	  x <= x + 1;
      end // always @ (posedge clk)
 endmodule // display
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