register values immediately after reading the from embedded ram (this is required for memories to get inferred)

1 files changed, 91 insertions, 39 deletions

diff --git a/design/vga.v b/design/vga.v
index e652ea6..b46dcbd 100644
--- a/design/vga.v
+++ b/design/vga.v
@@ -17,11 +17,11 @@
 
     /* Non-wishbone */
     input wire 	       clock_25mhz,
-    output reg 	       h_sync,
-    output reg 	       v_sync,
-    output reg [2:0]   red,
-    output reg [2:0]   green,
-    output reg [2:0]   blue
+    output wire        h_sync,
+    output wire        v_sync,
+    output wire [2:0]  red,
+    output wire [2:0]  green,
+    output wire [2:0]  blue
     );
 
    reg 		       powered_on;
@@ -156,18 +156,10 @@
       $readmemb(FONT_FILE, font, 0, 128 * 16 - 1);
    end
 
-   wire [6:0]  char_x;
-   wire [4:0]  char_y;
-   wire [12:0] char_flat_idx;
-   wire [15:0] text_memory_field;
-   wire [7:0]  char;
-   assign char_x = h_counter / 8;
-   assign char_y = v_counter / 16;
-   assign char_flat_idx = char_x + char_y * LINE_LENGTH;
-   assign text_memory_field = text_memory[char_flat_idx[12:1]];
-   assign char = char_flat_idx[0] ?
-		 text_memory_field[15:8] : text_memory_field[7:0];
+   parameter FG_COLOR = {3'b010, 3'b111, 3'b101};
+   parameter BG_COLOR = {3'b000, 3'b000, 3'b111};
 
+   /* display this for non-ascii characters */
    wire [0:7]  replacement_char [0:16];
    assign replacement_char[0]  = 8'b00000000;
    assign replacement_char[1]  = 8'b00011000;
@@ -186,38 +178,90 @@
    assign replacement_char[14] = 8'b00011000;
    assign replacement_char[15] = 8'b00000000;
 
-   wire [2:0]  char_pixel_x;
-   wire [3:0]  char_pixel_y;
+   wire [6:0]  char_x;
+   wire [4:0]  char_y;
+   wire [12:0] char_flat_idx;
+   assign char_x = h_counter / 8;
+   assign char_y = v_counter / 16;
+   assign char_flat_idx = char_x + char_y * LINE_LENGTH;
+
+   /*
+    * hs[0], vs[0], fetched_memory_field, is_high_byte, char, char_pixel_x[0],
+    * char_pixel_y and display_on[0] get loaded first, then, one tick later,
+    * hs[1], vs[1], char_pixel_x[1], display_on[1], char_pixel_row,
+    * replacement_pixel_row and is_ascii_char get loaded and finally, another
+    * tick later, color gets loaded
+    */
+   reg [2:0]   hs;
+   reg [2:0]   vs;
+   reg [15:0]  fetched_memory_field;
+   reg 	       is_high_byte;
+   reg [2:0]   char_pixel_x [1:0];
+   reg [3:0]   char_pixel_y;
+   reg [1:0]   display_on;
+   reg [0:7]   char_pixel_row;
+   reg [0:7]   replacement_pixel_row;
+   reg 	       is_ascii_char;
+   reg [8:0]   color;
+
+   wire [7:0]  char;
+   wire [0:7]  pixel_row_to_use;
    wire        pixel_on;
-   wire        display_on;
-   assign char_pixel_x = h_counter % 8;
-   assign char_pixel_y = v_counter % 16;
-   /* Replace non-ASCII characters (i.e. chars with values above 127) */
-   assign pixel_on = char[7] ? replacement_char[char_pixel_y][char_pixel_x] :
-		     font[char[6:0] * 16 + char_pixel_y][char_pixel_x];
-   assign display_on = h_stage == H_STAGE_ACTIVE_VIDEO &&
-		       v_stage == V_STAGE_ACTIVE_VIDEO;
+   assign char = is_high_byte ? fetched_memory_field[15:8] :
+		 fetched_memory_field[7:0];
+   assign pixel_row_to_use = is_ascii_char ? char_pixel_row :
+			     replacement_pixel_row;
+   assign pixel_on = pixel_row_to_use[char_pixel_x[1]];
 
-   parameter FG_COLOR = {3'b010, 3'b111, 3'b101};
-   parameter BG_COLOR = {3'b000, 3'b000, 3'b111};
+   /* Assign module's outputs */
+   assign h_sync = hs[2];
+   assign v_sync = vs[2];
+   assign {red, green, blue} = color;
 
    always @ (posedge clock_25mhz) begin
+      /* Stuff, that gets loaded first */
       if (h_stage == H_STAGE_SYNC)
-	h_sync <= H_POLARITY;
+	hs[0] <= H_POLARITY;
       else
-	h_sync <= ~H_POLARITY;
+	hs[0] <= ~H_POLARITY;
 
       if (v_stage == V_STAGE_SYNC)
-	v_sync <= V_POLARITY;
+	vs[0] <= V_POLARITY;
       else
-	v_sync <= ~V_POLARITY;
+	vs[0] <= ~V_POLARITY;
+
+      fetched_memory_field <= text_memory[char_flat_idx[12:1]];
+      is_high_byte <= char_flat_idx[0];
+
+      char_pixel_x[0] <= h_counter % 8;
+      char_pixel_y <= v_counter % 16;
+
+      display_on[0] <= h_stage == H_STAGE_ACTIVE_VIDEO &&
+		       v_stage == V_STAGE_ACTIVE_VIDEO;
+
+      /* Stuff, that gets loaded one tick later */
+      hs[1] <= hs[0];
+      vs[1] <= vs[0];
+
+      char_pixel_x[1] <= char_pixel_x[0];
+
+      display_on[1] <= display_on[0];
+
+      char_pixel_row <= font[char[6:0] * 16 + char_pixel_y];
+      replacement_pixel_row <= replacement_char[char_pixel_y];
+
+      is_ascii_char <= ~char[7];
+
+      /* Stuff, that gets loaded another tick later */
+      hs[2] <= hs[1];
+      vs[2] <= vs[1];
 
       if (!display_on)
-	{red, green, blue} <= 9'b0;
+	color <= 9'b0;
       else if (pixel_on)
-	{red, green, blue} <= FG_COLOR;
+	color <= FG_COLOR;
       else
-	{red, green, blue} <= BG_COLOR;
+	color <= BG_COLOR;
    end // always @ (posedge clock_25mhz)
 
 `ifdef SIMULATION
@@ -227,9 +271,18 @@
       powered_on_latched <= 0;
       ack <= 0;
 
-      h_sync <= ~H_POLARITY;
-      v_sync <= ~V_POLARITY;
-      {red, green, blue} <= 9'b0;
+      hs <= {3{~H_POLARITY}};
+      vs <= {3{~V_POLARITY}};
+      fetched_memory_field <= 16'b0;
+      is_high_byte <= 0;
+      char_pixel_x[0] <= 0;
+      char_pixel_x[1] <= 0;
+      char_pixel_y <= 0;
+      display_on <= 2'b0;
+      char_pixel_row <= 8'b0;
+      replacement_pixel_row <= 8'b0;
+      is_ascii_char <= 0;
+      color <= 9'b0;
 
       h_counter <= 0;
       h_stage <= H_STAGE_RB_OR_FP;
@@ -239,4 +292,3 @@
    end
 `endif
 endmodule // vga
-