1 files changed, 203 insertions, 0 deletions
diff --git a/models/vga_display.v b/models/vga_display.v
new file mode 100644
index 0000000..bb683e2
--- /dev/null
+++ b/models/vga_display.v
@@ -0,0 +1,203 @@
+`default_nettype none
+`timescale 1ns/1ns
+
+`include "messages.vh"
+
+`ifndef SIMULATION
+ `error_SIMULATION_not_defined
+; /* Cause syntax error */
+`endif
+
+module VGA_640_480_60Hz(
+			input wire 	 horizontal_sync,
+			input wire 	 vertical_sync,
+
+			input wire [2:0] red,
+			input wire [2:0] green,
+			input wire [2:0] blue,
+
+			output reg [9:0] image_writes
+			);
+   initial
+     image_writes <= 0;
+
+   parameter FRONT_PORCH = 0;
+   parameter SYNC_PULSE = 1;
+   parameter BACK_PORCH = 2;
+   parameter ACTIVE_VIDEO = 3;
+   parameter UNKNOWN_STATE = 4;
+
+   integer h_state;
+   integer v_state;
+   initial begin
+      h_state <= UNKNOWN_STATE;
+      v_state <= UNKNOWN_STATE;
+   end
+
+   parameter H_SYNC_POLARITY = 1'b0;
+   parameter H_FRONT_PORCH_LENGTH = 16;
+   parameter H_SYNC_PULSE_LENGTH = 96;
+   parameter H_BACK_PORCH_LENGTH = 48;
+   parameter H_ACTIVE_VIDEO_LENGTH = 640;
+
+   parameter V_SYNC_POLARITY = 1'b1;
+   parameter V_FRONT_PORCH_LENGTH = 10;
+   parameter V_SYNC_PULSE_LENGTH = 2;
+   parameter V_BACK_PORCH_LENGTH = 33;
+   parameter V_ACTIVE_VIDEO_LENGTH = 480;
+
+   reg [8:0] 				 picture
+					 [V_ACTIVE_VIDEO_LENGTH - 1 : 0]
+					 [H_ACTIVE_VIDEO_LENGTH - 1 : 0];
+
+   integer 				 h_counter, v_counter;
+
+   reg 					 error;
+
+   wire 				 unexpected_h_sync_pulse;
+   wire 				 missing_h_sync_pulse;
+   assign unexpected_h_sync_pulse = horizontal_sync == H_SYNC_POLARITY &&
+				    h_state != SYNC_PULSE;
+   assign missing_h_sync_pulse = horizontal_sync != H_SYNC_POLARITY &&
+				 h_state == SYNC_PULSE;
+
+   wire 				 unexpected_v_sync_pulse;
+   wire 				 missing_v_sync_pulse;
+   assign unexpected_v_sync_pulse = vertical_sync == V_SYNC_POLARITY &&
+				    v_state != SYNC_PULSE;
+   assign missing_v_sync_pulse = vertical_sync != V_SYNC_POLARITY &&
+				 v_state == SYNC_PULSE;
+
+   wire 				 new_line;
+   assign new_line = h_state == BACK_PORCH &&
+		     h_counter + 1 == H_BACK_PORCH_LENGTH;
+
+   wire 				 new_screen;
+   assign new_screen = v_state == BACK_PORCH &&
+		       v_counter + 1 == V_BACK_PORCH_LENGTH && new_line;
+
+   always #40 begin
+      /* First, horizontal stuff */
+      if (unexpected_h_sync_pulse) begin
+	 h_state <= SYNC_PULSE;
+	 h_counter <= 1;
+
+	 if (h_state != UNKNOWN_STATE) begin
+	   `MSG(({"VGA: error: unexpected horizontal sync pulse signal ",
+		  "(tick %0d; state %0d)"}, h_counter, h_state));
+	 end
+      end else if (missing_h_sync_pulse) begin
+	 h_state <= BACK_PORCH;
+	 h_counter <= 1;
+
+	 `MSG(({"VGA: error: missing expected horizontal sync pulse signal ",
+	       "(tick %0d of sync pulse)"}, h_counter));
+      end else begin
+	 case (h_state)
+	   FRONT_PORCH : begin
+	      if (h_counter + 1 != H_FRONT_PORCH_LENGTH) begin
+		 h_counter <= h_counter + 1;
+	      end else begin
+		 h_state <= SYNC_PULSE;
+		 h_counter <= 0;
+	      end
+	   end
+	   SYNC_PULSE : begin
+	      if (h_counter + 1 != H_SYNC_PULSE_LENGTH) begin
+		 h_counter <= h_counter + 1;
+	      end else begin
+		 h_state <= BACK_PORCH;
+		 h_counter <= 0;
+	      end
+	   end
+	   BACK_PORCH : begin
+	      if (h_counter + 1 != H_BACK_PORCH_LENGTH) begin
+		 h_counter <= h_counter + 1;
+	      end else begin
+		 h_state <= ACTIVE_VIDEO;
+		 h_counter <= 0;
+	      end
+	   end
+	   ACTIVE_VIDEO : begin
+	      if (v_state == ACTIVE_VIDEO) begin
+		 picture[v_counter][h_counter] <= {red, green, blue};
+	      end
+
+	      if (h_counter + 1 != H_ACTIVE_VIDEO_LENGTH) begin
+		 h_counter <= h_counter + 1;
+	      end else begin
+		 h_state <= FRONT_PORCH;
+		 h_counter <= 0;
+	      end
+	   end // case: ACTIVE_VIDEO
+	 endcase // case (h_state)
+      end // else: !if(missing_h_sync_pulse)
+
+
+      /* Vertical stuff is almost entirely the same as horizontal */
+      if (new_line) begin
+	 if (unexpected_v_sync_pulse) begin
+	    v_state <= SYNC_PULSE;
+	    v_counter <= 1;
+
+	    if (v_state != UNKNOWN_STATE) begin
+	       `MSG(({"VGA: error: unexpected vertical sync pulse signal ",
+		      "(line %0d; state %0d)"}, v_counter, v_state));
+	    end
+	 end else if (missing_v_sync_pulse) begin
+	    v_state <= BACK_PORCH;
+	    v_counter <= 1;
+
+	    `MSG(({"VGA: error: missing expected vertical sync pulse signal ",
+		   "(line %0d of sync pulse)"}, v_counter));
+	 end else begin
+	    case (v_state)
+	      FRONT_PORCH : begin
+		 if (v_counter + 1 != V_FRONT_PORCH_LENGTH) begin
+		    v_counter <= v_counter + 1;
+		 end else begin
+		    v_state <= SYNC_PULSE;
+		    v_counter <= 0;
+		 end
+	      end
+	      SYNC_PULSE : begin
+		 if (v_counter + 1 != V_SYNC_PULSE_LENGTH) begin
+		    v_counter <= v_counter + 1;
+		 end else begin
+		    v_state <= BACK_PORCH;
+		    v_counter <= 0;
+		 end
+	      end
+	      BACK_PORCH : begin
+		 if (v_counter + 1 != V_BACK_PORCH_LENGTH) begin
+		    v_counter <= v_counter + 1;
+		 end else begin
+		    v_state <= ACTIVE_VIDEO;
+		    v_counter <= 0;
+		 end
+	      end
+	      ACTIVE_VIDEO : begin
+		 if (v_counter + 1 != V_ACTIVE_VIDEO_LENGTH) begin
+		    v_counter <= v_counter + 1;
+		 end else begin
+		    v_state <= FRONT_PORCH;
+		    v_counter <= 0;
+
+		    if (!error) begin
+		       $writememb("VGAdump.mem", picture);
+		       `DBG(("VGA: written VGAdump.mem"));
+		       image_writes <= image_writes + 1;
+		    end
+		 end // else: !if(v_counter + 1 != V_ACTIVE_VIDEO_LENGTH)
+	      end // case: ACTIVE_VIDEO
+	    endcase // case (v_state)
+	 end // else: !if(missing_v_sync_pulse)
+      end // if (new_line)
+
+      if (unexpected_h_sync_pulse || unexpected_h_sync_pulse ||
+	  ((unexpected_v_sync_pulse || missing_v_sync_pulse) && new_line))
+	error <= 1;
+      else if (new_screen)
+	error <= 0;
+   end // always #40
+endmodule // VGA_640_480_60Hz