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nes2hdmi.sv
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// NES video and sound to HDMI converter
// nand2mario, 2022.9
`timescale 1ns / 1ps
module nes2hdmi (
input clk, // nes clock
input resetn,
// nes video signals
input [5:0] color,
input [8:0] cycle,
input [8:0] scanline,
input [15:0] sample,
input aspect_8x7, // 1: 8x7 pixel aspect ratio mode
// overlay interface
input overlay,
output [7:0] overlay_x,
output [7:0] overlay_y,
input [14:0] overlay_color, // BGR5
// video clocks
input clk_pixel,
input clk_5x_pixel,
// output [7:0] led,
// output signals
output tmds_clk_n,
output tmds_clk_p,
output [2:0] tmds_d_n,
output [2:0] tmds_d_p
);
// NES generates 256x240. We assume the center 256x224 is visible and scale that to 4:3 aspect ratio.
// https://www.nesdev.org/wiki/Overscan
localparam FRAMEWIDTH = 1280;
localparam FRAMEHEIGHT = 720;
localparam TOTALWIDTH = 1650;
localparam TOTALHEIGHT = 750;
localparam SCALE = 5;
localparam VIDEOID = 4;
localparam VIDEO_REFRESH = 60.0;
// localparam IDIV_SEL_X5 = 3;
// localparam FBDIV_SEL_X5 = 54;
// localparam ODIV_SEL_X5 = 2;
// localparam DUTYDA_SEL_X5 = "1000";
// localparam DYN_SDIV_SEL_X5 = 2;
localparam CLKFRQ = 74250;
localparam COLLEN = 80;
localparam AUDIO_BIT_WIDTH = 16;
localparam POWERUPNS = 100000000.0;
localparam CLKPERNS = (1.0/CLKFRQ)*1000000.0;
localparam int POWERUPCYCLES = $rtoi($ceil( POWERUPNS/CLKPERNS ));
// video stuff
wire [9:0] cy, frameHeight;
wire [10:0] cx, frameWidth;
//
// BRAM frame buffer
//
localparam MEM_DEPTH=256*240;
localparam MEM_ABITS=16;
logic [5:0] mem [0:256*240-1];
logic [15:0] mem_portA_addr;
logic [5:0] mem_portA_wdata;
logic mem_portA_we;
wire [15:0] mem_portB_addr;
logic [5:0] mem_portB_rdata;
// BRAM port A read/write
always_ff @(posedge clk) begin
if (mem_portA_we) begin
mem[mem_portA_addr] <= mem_portA_wdata;
end
end
// BRAM port B read
always_ff @(posedge clk_pixel) begin
mem_portB_rdata <= mem[mem_portB_addr];
end
initial begin
$readmemb("background.txt", mem);
end
//
// Data input and initial background loading
//
logic [8:0] r_scanline;
logic [8:0] r_cycle;
always @(posedge clk) begin
r_scanline <= scanline;
r_cycle <= cycle;
mem_portA_we <= 1'b0;
if ((r_scanline != scanline || r_cycle != cycle) && scanline < 9'd240 && ~cycle[8]) begin
mem_portA_addr <= {scanline[7:0], cycle[7:0]};
mem_portA_wdata <= color;
mem_portA_we <= 1'b1;
end
end
// audio stuff
// localparam AUDIO_RATE=32000; // weird only 32K sampling rate works
// localparam AUDIO_RATE=96000;
localparam AUDIO_RATE=48000;
localparam AUDIO_CLK_DELAY = CLKFRQ * 1000 / AUDIO_RATE / 2;
logic [$clog2(AUDIO_CLK_DELAY)-1:0] audio_divider;
logic clk_audio;
always_ff@(posedge clk_pixel)
begin
if (audio_divider != AUDIO_CLK_DELAY - 1)
audio_divider++;
else begin
clk_audio <= ~clk_audio;
audio_divider <= 0;
end
end
reg [15:0] audio_sample_word [1:0], audio_sample_word0 [1:0];
always @(posedge clk_pixel) begin // crossing clock domain
audio_sample_word0[0] <= sample;
audio_sample_word[0] <= audio_sample_word0[0];
audio_sample_word0[1] <= sample;
audio_sample_word[1] <= audio_sample_word0[1];
end
//
// Video
// Scale 256x224 to 1280x720
//
localparam WIDTH=256;
localparam HEIGHT=240;
reg [23:0] rgb; // actual RGB output
reg active /* xsynthesis syn_keep=1 */;
reg [$clog2(WIDTH)-1:0] xx /* xsynthesis syn_keep=1 */; // scaled-down pixel position
reg [$clog2(HEIGHT)-1:0] yy /* xsynthesis syn_keep=1 */;
reg [10:0] xcnt /* xsynthesis syn_keep=1 */;
reg [10:0] ycnt /* xsynthesis syn_keep=1 */; // fractional scaling counters
reg [9:0] cy_r;
assign mem_portB_addr = yy * WIDTH + xx + 8*256;
assign overlay_x = xx;
assign overlay_y = yy;
localparam XSTART = (1280 - 960) / 2; // 960:720 = 4:3
localparam XSTOP = (1280 + 960) / 2;
// address calculation
// Assume the video occupies fully on the Y direction, we are upscaling the video by `720/height`.
// xcnt and ycnt are fractional scaling counters.
always @(posedge clk_pixel) begin
reg active_t;
reg [10:0] xcnt_next;
reg [10:0] ycnt_next;
xcnt_next = xcnt + 256;
ycnt_next = ycnt + 224;
active_t = 0;
if (cx == XSTART - 1) begin
active_t = 1;
active <= 1;
end else if (cx == XSTOP - 1) begin
active_t = 0;
active <= 0;
end
if (active_t | active) begin // increment xx
xcnt <= xcnt_next;
if (xcnt_next >= 960) begin
xcnt <= xcnt_next - 960;
xx <= xx + 1;
end
end
cy_r <= cy;
if (cy[0] != cy_r[0]) begin // increment yy at new lines
ycnt <= ycnt_next;
if (ycnt_next >= 720) begin
ycnt <= ycnt_next - 720;
yy <= yy + 1;
end
end
if (cx == 0) begin
xx <= 0;
xcnt <= 0;
end
if (cy == 0) begin
yy <= 0;
ycnt <= 0;
end
end
// calc rgb value to hdmi
reg [23:0] NES_PALETTE [0:63];
always @(posedge clk_pixel) begin
if (active) begin
if (overlay)
rgb <= {overlay_color[4:0],3'b0,overlay_color[9:5],3'b0,overlay_color[14:10],3'b0}; // BGR5 to RGB8
else
rgb <= NES_PALETTE[mem_portB_rdata];
end else
rgb <= 24'h303030;
end
// HDMI output.
logic[2:0] tmds;
hdmi #( .VIDEO_ID_CODE(VIDEOID),
.DVI_OUTPUT(0),
.VIDEO_REFRESH_RATE(VIDEO_REFRESH),
.IT_CONTENT(1),
.AUDIO_RATE(AUDIO_RATE),
.AUDIO_BIT_WIDTH(AUDIO_BIT_WIDTH),
.START_X(0),
.START_Y(0) )
hdmi( .clk_pixel_x5(clk_5x_pixel),
.clk_pixel(clk_pixel),
.clk_audio(clk_audio),
.rgb(rgb),
.reset( 0 ),
.audio_sample_word(audio_sample_word),
.tmds(tmds),
.tmds_clock(tmdsClk),
.cx(cx),
.cy(cy),
.frame_width( frameWidth ),
.frame_height( frameHeight ) );
// Gowin LVDS output buffer
ELVDS_OBUF tmds_bufds [3:0] (
.I({clk_pixel, tmds}),
.O({tmds_clk_p, tmds_d_p}),
.OB({tmds_clk_n, tmds_d_n})
);
// 2C02 palette: https://www.nesdev.org/wiki/PPU_palettes
assign NES_PALETTE[0] = 24'h545454; assign NES_PALETTE[1] = 24'h001e74; assign NES_PALETTE[2] = 24'h081090; assign NES_PALETTE[3] = 24'h300088;
assign NES_PALETTE[4] = 24'h440064; assign NES_PALETTE[5] = 24'h5c0030; assign NES_PALETTE[6] = 24'h540400; assign NES_PALETTE[7] = 24'h3c1800;
assign NES_PALETTE[8] = 24'h202a00; assign NES_PALETTE[9] = 24'h083a00; assign NES_PALETTE[10] = 24'h004000; assign NES_PALETTE[11] = 24'h003c00;
assign NES_PALETTE[12] = 24'h00323c; assign NES_PALETTE[13] = 24'h000000; assign NES_PALETTE[14] = 24'h000000; assign NES_PALETTE[15] = 24'h000000;
assign NES_PALETTE[16] = 24'h989698; assign NES_PALETTE[17] = 24'h084cc4; assign NES_PALETTE[18] = 24'h3032ec; assign NES_PALETTE[19] = 24'h5c1ee4;
assign NES_PALETTE[20] = 24'h8814b0; assign NES_PALETTE[21] = 24'ha01464; assign NES_PALETTE[22] = 24'h982220; assign NES_PALETTE[23] = 24'h783c00;
assign NES_PALETTE[24] = 24'h545a00; assign NES_PALETTE[25] = 24'h287200; assign NES_PALETTE[26] = 24'h087c00; assign NES_PALETTE[27] = 24'h007628;
assign NES_PALETTE[28] = 24'h006678; assign NES_PALETTE[29] = 24'h000000; assign NES_PALETTE[30] = 24'h000000; assign NES_PALETTE[31] = 24'h000000;
assign NES_PALETTE[32] = 24'heceeec; assign NES_PALETTE[33] = 24'h4c9aec; assign NES_PALETTE[34] = 24'h787cec; assign NES_PALETTE[35] = 24'hb062ec;
assign NES_PALETTE[36] = 24'he454ec; assign NES_PALETTE[37] = 24'hec58b4; assign NES_PALETTE[38] = 24'hec6a64; assign NES_PALETTE[39] = 24'hd48820;
assign NES_PALETTE[40] = 24'ha0aa00; assign NES_PALETTE[41] = 24'h74c400; assign NES_PALETTE[42] = 24'h4cd020; assign NES_PALETTE[43] = 24'h38cc6c;
assign NES_PALETTE[44] = 24'h38b4cc; assign NES_PALETTE[45] = 24'h3c3c3c; assign NES_PALETTE[46] = 24'h000000; assign NES_PALETTE[47] = 24'h000000;
assign NES_PALETTE[48] = 24'heceeec; assign NES_PALETTE[49] = 24'ha8ccec; assign NES_PALETTE[50] = 24'hbcbcec; assign NES_PALETTE[51] = 24'hd4b2ec;
assign NES_PALETTE[52] = 24'hecaeec; assign NES_PALETTE[53] = 24'hecaed4; assign NES_PALETTE[54] = 24'hecb4b0; assign NES_PALETTE[55] = 24'he4c490;
assign NES_PALETTE[56] = 24'hccd278; assign NES_PALETTE[57] = 24'hb4de78; assign NES_PALETTE[58] = 24'ha8e290; assign NES_PALETTE[59] = 24'h98e2b4;
assign NES_PALETTE[60] = 24'ha0d6e4; assign NES_PALETTE[61] = 24'ha0a2a0; assign NES_PALETTE[62] = 24'h000000; assign NES_PALETTE[63] = 24'h000000;
endmodule