Electronics > FPGA

FPGA VGA Controller for 8-bit computer

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nockieboy:

--- Quote from: BrianHG on June 24, 2022, 08:40:06 pm ---In my above link, don't forget to download my final .zip showing you how to parallel simulate your VHDL vs Verilog to proof your design.
--- End quote ---

I think I'll stick with the VHDL.  I don't think I'll gain much from translating it to Verilog, I was just wondering if there was an easy way to do it.

In other news, I seem to be hitting some glitches in the GPU.  I've noticed that the display on the TV keeps cutting out, quite frequently at first, almost as if the screen display is changing mode or the HDMI cable is loose (it's not).  After a few minutes it seems to stabilise and not do it any more.

Another glitch I noticed earlier today whilst writing some code to display a cursor caret in the DMI.  I noticed these vertical blue lines down the left edge of the screen - a little flickery, there for a short time, then disappeared, then reappeared briefly a few times then went completely.  Hadn't noticed these before.  Here's a pic:



Any ideas what could be causing this?

BrianHG:
(Wait... before the rest, I used to get this problem before changing my HDMI cable as the plug on the DECA board keeps on eating a contact in my HDMI cable every time I plug one in and out a few times...)

If not the cable, then:

Strange.  What does your final timing report say?
It looks like a problem with the HDMI data or CLK line timing or noise.
Are you powering your project from USB alone, or using the power supply?  What happens if you insert or remove the SD card?
How warm is the FPGA getting?  What happens if you cool it?
Note that mine runs cool, however, my ellipse demo is a far simpler design.

If all else fails, send an update of your latest complete project with a 1mb RS232 debug capture file of your system where those blue dots appear to see if I can see them here.

BrianHG:
Note that some of my above point may be that you could be overloading the onboard switcher PSU and you are seeing noise during my DDR3 video line buffer bursting which runs at the full 1600mb/sec once every H-sync.

The system limit of the DECA is ~2 watts when powered by the USB.
Are you powering any of you Z80 circuitry as well?

(note that on my side, I found the DECA hdmi transmitter is really weak.  I even had to ensure that my monitor's AC plug when into the same power bar as my PC powering the DECA for 1080p to work.  (Most likely frame GND interference via a gigantic GND loop)  This is not a DDR3 issue as either an active HDMI cable amplifier or a really short cable would also solve the issue on my side.)

nockieboy:

--- Quote from: BrianHG on July 04, 2022, 07:51:19 pm ---Note that some of my above point may be that you could be overloading the onboard switcher PSU and you are seeing noise during my DDR3 video line buffer bursting which runs at the full 1600mb/sec once every H-sync.

The system limit of the DECA is ~2 watts when powered by the USB.
Are you powering any of you Z80 circuitry as well?

(note that on my side, I found the DECA hdmi transmitter is really weak.  I even had to ensure that my monitor's AC plug when into the same power bar as my PC powering the DECA for 1080p to work.  (Most likely frame GND interference via a gigantic GND loop)  This is not a DDR3 issue as either an active HDMI cable amplifier or a really short cable would also solve the issue on my side.)
--- End quote ---

It's a really intermittent issue, which makes it hard to solve.  More often than not, there's no issue - perhaps one time in ten or more I see screen blanking, I saw the blue lines down the side for the first time when I took the picture yesterday.

I've tried wiggling (gently) the HDMI connector, haven't noticed any interference as a result and the image is rock-steady today.

I am currently powering both the DECA and the uCOM from the same USB 3.1 port for convenience.  The entire setup is drawing about 0.85A - which is close to the maximum 900mA for a standard USB 3 port. :-\  I can always connect the DECA via another USB port (i.e. one off the back of the PC) to split the power demand, this takes the uCOM's power draw down to just under 2.5W.

I'll see if I can get temperatures and more information the next time the issue crops up.

BrianHG:
It may not be the USB port limit, but DECA's the onboard PSP which may be designed for the 500ma limit of USB1.

As for intermittent, remember to grab the RS232 debugger and capture 1mb snapshot when you see the problem.

The you TX the 1mb file lateron when the problem isn't there to see if it comes back.

You can also try changing the HDMI from HDMI mode to DVI mode in the I2C controls to see if that helps.

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