mango_one/hvsync_generator.v
2019-09-02 20:31:40 -04:00

70 lines
2.1 KiB
Verilog

`ifndef HVSYNC_GENERATOR_H
`define HVSYNC_GENERATOR_H
/*
Video sync generator, used to drive a simulated CRT.
To use:
- Wire the hsync and vsync signals to top level outputs
- Add a 3-bit (or more) "rgb" output to the top level
*/
module hvsync_generator(clk, reset, hsync, vsync, display_on, hpos, vpos);
input clk;
input reset;
output reg hsync, vsync;
output display_on;
output reg [8:0] hpos;
output reg [8:0] vpos;
// declarations for TV-simulator sync parameters
// horizontal constants
parameter H_DISPLAY = 256; // horizontal display width
parameter H_BACK = 23; // horizontal left border (back porch)
parameter H_FRONT = 7; // horizontal right border (front porch)
parameter H_SYNC = 23; // horizontal sync width
// vertical constants
parameter V_DISPLAY = 240; // vertical display height
parameter V_TOP = 5; // vertical top border
parameter V_BOTTOM = 14; // vertical bottom border
parameter V_SYNC = 3; // vertical sync # lines
// derived constants
parameter H_SYNC_START = H_DISPLAY + H_FRONT;
parameter H_SYNC_END = H_DISPLAY + H_FRONT + H_SYNC - 1;
parameter H_MAX = H_DISPLAY + H_BACK + H_FRONT + H_SYNC - 1;
parameter V_SYNC_START = V_DISPLAY + V_BOTTOM;
parameter V_SYNC_END = V_DISPLAY + V_BOTTOM + V_SYNC - 1;
parameter V_MAX = V_DISPLAY + V_TOP + V_BOTTOM + V_SYNC - 1;
wire hmaxxed = (hpos == H_MAX) || reset; // set when hpos is maximum
wire vmaxxed = (vpos == V_MAX) || reset; // set when vpos is maximum
// horizontal position counter
always @(posedge clk)
begin
hsync <= (hpos>=H_SYNC_START && hpos<=H_SYNC_END);
if(hmaxxed)
hpos <= 0;
else
hpos <= hpos + 1;
end
// vertical position counter
always @(posedge clk)
begin
vsync <= (vpos>=V_SYNC_START && vpos<=V_SYNC_END);
if(hmaxxed)
if (vmaxxed)
vpos <= 0;
else
vpos <= vpos + 1;
end
// display_on is set when beam is in "safe" visible frame
assign display_on = (hpos<H_DISPLAY) && (vpos<V_DISPLAY);
endmodule
`endif