[Open-graphics] Help with specs on TV chip?

[Nicholas]

> Could someone help me with the spec on the TV chip?  In other words,
> could I get someone to read it for me and then answer specific
> questions?

I can look through it, and try to help, but I don't really have any
experience with anything beyond simple NTSC in the video category.

> Actually, at the moment, the main question is what is the pixel
> interface like?  It appears to be DDR, very much like a single-link
> DVI transmitter.

Do you have a link to the datasheet? I couldn't find it anywhere on the
wiki.

I made a really bad test interface for the DVI output module.
This was really quickly hacked together. It is supposed to be a signal
generator for the video, but I am sure it fails miserably since I
haven't done Verilog in a while and don't really understand DVI video
sync. I had two big questions about what I was writing:
1) how do you define constants? I like having nice descriptive names,
and constants allow me to easily change the value. I googled it and
found "specparam", but it wasn't working.
2) What is the difference between "<=" and "="? I thought that "=" was
non-blocking, but after rereading your tutorial, I came across:

	If you were to use blocking assignments, this is what you'd get:

	always @(posedge clock) begin
	x = in + 1;
	y = x + 1;
	z = y + 1;
	end

	time: values
	0: in=3, x='hx, y='hx, z='hx
	1: in=3, x=4, y=5, z=6

I don't understand how this is blocking, since all the computation
occurs in a single time period?
What I want for this code is that assignments like so:
		hstate <= 0;
		horiz <=0;
		vert <=0;
		vstate <=0;
are non-blocking, so that they execute in parallel, correct?

Also, is there a good resource that explains the DVI interface? I wasn't
really sure what I should send in terms of syncs, porches, etc...

Thanks!


// 800 X 600 @ 60Hz with a 40.000MHz pixel clock
module sync_const;
specparam 	H_ACTIVE =	800,	// pixels
 		H_FRONT_PORCH =	40,	// pixels
		H_SYNCH =	128,	// pixels
		H_BACK_PORCH =	88,	// pixels
		H_TOTAL = 	1056,	// pixels
		V_ACTIVE =	600,	// lines
		V_FRONT_PORCH =	1,	// lines
		V_SYNCH =	4,	// lines
		V_BACK_PORCH =	23,	// lines
		V_TOTAL =	628;	// lines

specparam 	SYNC_DATA_STATE=0,
		PORCH_DATA_STATE=1b'111111111111111111111111111111,
		COLOR_DATA_STATE=0;

wire clock;
wire clock_2x;
wire reset;
wire [29:0] vidout;

reg [29:0] vid_data; //29:20 R, 19:10 G, 9:0 B
reg clk;
reg [9:0] vert; //current vertical scanline location
reg [11:0] horiz; //current pixel in scanline
reg [1:0] hstate; //horizontal and vertical states
reg [1:0] vstate; //so it is easier to ref them.

assign clock=clk;
initial begin
	vert=0; horiz=0;
end
always begin
	#5 clk=~clk;
end

always @(posedge clk)
begin
	horiz <= horiz + 1;
	if (horiz>H_TOTAL)
	begin
		hstate <= 0;
		horiz <=0;
		vert <= vert + 1;
	end else if (horiz >  H_SYNCH + 
		H_FRONT_PORCH + H_ACTIVE)
	begin
		hstate <= 3;
	end else if (horiz > 
		H_FRONT_PORCH + H_ACTIVE)
	begin
		hstate <= 2;
	end else if (horiz > H_ACTIVE)
	begin
		hstate <= 1;
	end
	//now all the states are correct:
	//0) Active - White.
	//1) Front Porch.
	//2) Sync signal. 0.
	//3) Back Porch.
	//Now set up Vert in the same way... 
	if (vert>V_TOTAL)
	begin
		hstate <= 0;
		horiz <=0;
		vert <=0;
		vstate <=0;
		// new frame
	end else if (vert >  V_SYNCH + 
		V_FRONT_PORCH + V_ACTIVE)
	begin
		vstate <= 3;
	end else if (vert > 
		V_FRONT_PORCH + V_ACTIVE)
	begin
		vstate <= 2;
	end else if (vert > V_ACTIVE)
	begin
		vstate <= 1;
	end
	//now all is ready.
	//insert here the code to make colors based
	//on the various values.
	//example: just sync signals.
	if (vstate==2) //sync state
	begin
		vid_data<=SYNC_DATA_STATE;
	end
	if (hstate==2) //sync state
	begin
		vid_data<=SYNC_DATA_STATE;
	end
	if (hstate==1 || hstate==3) //porch state
	begin
		vid_data<=PORCH_DATA_STATE;
	end
	if (vstate==1 || vstate==3) //sync state
	begin
		vid_data<=PORCH_DATA_STATE;
	end
	if (hstate==0 && vstate==0) //draw state
	begin
		vid_data<=COLOR_DATA_STATE; //this is where you can add
			// Based on the x and y locations on the screen, horiz and vert.
	end
	$display("%g time; hstate %d, vstate %d. horiz=%d, vert=%d.\n",
$time,hstate,vstate,horiz,vert);
end
//head0_video_out u0(clock,clock_2x,reset,vidout,,,,,,,);
//I dunno what dvi_de, dvi_m_clk, dvi_s_clk are for... and we aren't
using
//dac_* for now, right?
endmodule