display: latch a local copy of fg_ctlabc80-de1-18

fg_ctl is set in another clock domain, so latch a local copy in the
video_clk domain.  While we're doing that, we might as well defer
the switch until vertical blank.

1 files changed, 8 insertions, 3 deletions

diff --git a/display.v b/display.v
index 3360138..81886b7 100644
--- a/display.v
+++ b/display.v
@@ -94,6 +94,7 @@ module display (
    reg 		 prefetch;	// True for the prefetch character position
 
    // Fine Graphics control
+   reg [7:0] 	 fgctl_q;	// Latched version of fg_ctl
    reg [7:0] 	 fgpixels;	// One byte of fg pixels
    
    // For the current text line
@@ -200,13 +201,17 @@ module display (
    wire [3:0] 	 fg_argb;
 
    always @(posedge clk)
+     if ( ~yvideo )		// Only change mode during vertical blank
+       fgctl_q <= fg_ctl;
+
+   always @(posedge clk)
      if (x[2:0] == 3'b100)
        fgpixels <= fg_data;
      else if (~x[0])
        fgpixels <= { fgpixels[5:0], 2'bxx };
 
    fgcolrom fgcolrom (
-		      .address ( { fg_ctl[6:0], fgpixels[7:6] } ),
+		      .address ( { fgctl_q[6:0], fgpixels[7:6] } ),
 		      .clock ( clk ),
 		      .q ( fg_argb )
 		      );
@@ -220,11 +225,11 @@ module display (
 	else if ( testpattern )
 	  // Pixel test pattern for LCD monitor calibration
 	  rgb <= {3{x[0] ^ y[0]}};
-	else if ( ~fg_ctl[7] & pixrow[5]
+	else if ( ~fgctl_q[7] & pixrow[5]
 		  & ~(do_flsh & ~flash_on)
 		  & ~(do_hide & ~reveal) )
 	  rgb <= fg ^ {3{invert}};
-	else if (fg_ctl[7] | fg_argb[3])
+	else if (fgctl_q[7] | fg_argb[3])
 	  rgb <= fg_argb[2:0];
 	else
 	  rgb <= bg ^ {3{invert}};