Fixed Quartus VGA reversal bug/feature. Removed bit reversing logic and created bit-reversed font rom hex file

roms/vga_font_bitreversed.hex

@@ -0,0 +1,640 @@
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rtl/boards/terasic_de0/apple1_de0_top.v

@@ -120,6 +120,8 @@ module apple1_de0_top(
     //  cnt <= cnt + 1;
     //end
     
+    
+    
     assign LEDG = 0;
     
 endmodule

rtl/vga/font_rom.v

@@ -34,9 +34,9 @@ module font_rom(
     );
 
     `ifdef SIM
-    parameter ROM_FILENAME = "../roms/vga_font.hex";
+    parameter ROM_FILENAME = "../roms/vga_font_bitreversed.hex";
     `else
-    parameter ROM_FILENAME = "../../roms/vga_font.hex";
+    parameter ROM_FILENAME = "../../roms/vga_font_bitreversed.hex";
     `endif
 
     reg [7:0] rom[0:1023];
@@ -44,15 +44,22 @@ module font_rom(
     initial
         $readmemh(ROM_FILENAME, rom, 0, 1023);
 
-    // double width of pixel by ignoring bit 0
-    wire [2:0] pixel_ptr;
-    
-    //assign pixel_ptr = (3'h7 - pixel[3:1]);
-    assign pixel_ptr = pixel[3:1];
-
     // double height of pixel by ignoring bit 0
     wire [3:0] line_ptr = line[4:1];
 
+    // Note: Quartus II reverses the pixels when we do:
+    //
+    // rom[address][bitindex] 
+    //
+    // directly, so we use an intermediate 
+    // signal, romout, to work around this 
+    // problem.
+    //
+    // IceCube2 and Yosys don't seem to have this problem.
+    //
+    
+    reg [7:0] romout;
+    
     always @(posedge clk)
     begin
         // mode
@@ -60,9 +67,12 @@ module font_rom(
         // 01 - vertical scanlines
         // 10 - horizontal scanlines
         // 11 - dotty mode
+        
+        romout = rom[(character * 10) + {2'd0, line_ptr}];
+        
         out <= (mode[1] & line[0]) ? 1'b0 :
                (mode[0] & pixel[0]) ? 1'b0 :
-               rom[(character * 10) + {2'd0, line_ptr}][pixel_ptr];
+               romout[pixel[3:1]];
     end
 
 endmodule

tools/vgaromgen/main.c

@@ -20,40 +20,40 @@ int main(int argc, char *argv[])
         return 1;
     }
     
-    FILE *fout = fopen("../../roms/vga_font.hex","wt");
+    FILE *fout = fopen("../../roms/vga_font_bitreversed.hex","wt");
     if (fout == NULL)
     {
-        printf("Error: cannot open vga_font.hex for writing!\n");        
+        printf("Error: cannot open vga_font_bitreversed.hex for writing!\n");        
         fclose(fin);
         return 1;        
     }
     
     uint8_t count = 0;
-    uint8_t nibble = 0;
-    uint32_t bitcount = 0;
+    uint8_t byte = 0;
+    uint32_t bytecount = 0;
     while(!feof(fin))
     {
         char c = fgetc(fin);
         if ((c == '0') || (c == '1'))
         {
-            nibble <<= 1;
-            nibble = nibble | (c - '0');
+            byte >>= 1;
+            if (c == '1')
+                byte |= 0x80;
+            
             count++;
-            if (count == 4)
+            if (count == 8)
             {
-                fprintf(fout, "%c", hextbl[nibble]);
+                fprintf(fout, "%c", hextbl[byte >> 4]);
+                fprintf(fout, "%c", hextbl[byte & 0x0F]);
+                fprintf(fout, "\n");
                 count = 0;
-                nibble = 0;
-                if ((bitcount % 8) == 7)
-                {
-                    fprintf(fout, "\n");
-                }
+                byte = 0;
+                bytecount++;
             }
-            bitcount++;
         }
     }
     
-    printf("Done: converted %d bits\n", bitcount);
+    printf("Done: converted %d bytes\n", bytecount);
     
     fclose(fout);
     fclose(fin);