Exploring FPGA Graphics

The purpose of this site is to teach the fundamentals of creating graphics and having them show up on an external display. Driving a VGA signal is extremely straightforward compared to the complexity of HDMI. Generating an HDMI signal is arguably not the main goal of the site, so using VGA makes total sense imo.

I think from a hardware perspective this would be non-trivial, despite sounding like an obvious thing in principle.

In sending the entire frame with every refresh you get pixel addressing "for free", since you just send the data for each pixel sequentially in a predefined order. If you only wanted to update a single pixel, you would need to effectively send an instruction saying "set pixel x to rgb: a, b, c" or whatever, including both the pixel colour values and the pixel address. You'd also need some sort of edge detection for when a pixel is supposed to change which adds a delay.

This is fine for one pixel, but if every pixel on the screen changes at once then suddenly you are going to be sending a hell of a lot of instructions that not only contain the colour values as in the "old crt style" method, but also the address of every individual pixel too, which will then have to be decoded by the screen-side hardware.

All in all, you'll be using a lot more bandwidth and will need a much faster clock to do all of that in the same period of time. In the old school way, you just have a pixel clock that matches the pixel rate and some serdes for serialisation/deserialisation on each end which imo is considerably simpler.

VGA is incredibly easy to generate - you can do it via bitbanging (carefully turning on and off) GPIO pins on an Arduino [1], simply because the tolerances are insanely huge. A step above is SD-SDI [2], which uses less pins but has stricter requirements on timing, and equipment accepting SDI is usually only found in the professional-grade TV production space.

DVI, HDMI, DisplayPort or heaven forbid Thunderbolt are a hot mess - to generate a signal out of these without the usage of dedicated chips, you need a ton of logic and parts: output format negotiation, extremely strict timing requirements that completely rule out bitbanging, signal conditioning, specially shielded cables, shielded traces on the circuit board.

[1] https://hackaday.com/2014/06/10/640x480-vga-on-an-arduino/

[2] https://en.wikipedia.org/wiki/Serial_digital_interface

The examples aren’t limited to VGA; I support four different outputs with these designs.

* VGA using a Pmod board (you could also create your own register ladder)

* DVI using the TI TFP410 on the DVI Pmod board

* DVI generated on FPGA with a Verilog TMDS encoder (no IC required)

* SDL simulation on a PC

DVI is a subset of HDMI, so works on modern TVs and monitors.

You can find the source on GitHub: https://github.com/projf/projf-explore/tree/main/graphics/fp...

Oh, I’ll get to that :D