RP-CVideo

Generate a binary/monochrome composite video signal on the RP2040 and RP235x MCUs

Features

• Clock cycle consistent timing
• Supports progressive and interlaced video
• Supports single and double buffering
• Supports non-standard stuff like:
  • Different number of display lines
  • Bigger or smaller front/back porch (horizontal margins)
  • Fewer or more blank lines on top and bottom
  • Non-square pixels
  • Different frame-rates
  • And more
  • These options can be useful when you're using one of those old 80's CRT monitors with adjustment knobs, which allows you - for example - to trade a bit of framerate for vertical resolution or the other way around.
• Uses one only one PIO state-machine (and 13 instructions)
• Supports non-standard system clock frequencies
• Optional embedded_graphics driver, which allows you to draw common shapes and text.
• Stores pixel data efficiently using 1 bit per pixel. To give an idea, in single-buffer / progressive mode, with a resolution of 400x250 you need about 21kb. There is some overhead for all the non visible portions of the composite signal.
• Const time configuration. Allows for perfectly sized static buffer allocation and catching many configuration mistakes at compile time.

Limitations

(PR's welcome)

• No colors
• Currently only supports 2 level black/white level monochrome. More levels might be possible with some modifications
• No per line-buffering, it has to keep at least one whole frame/field in memory
• No feedback on being too late with commiting the next frame, other than seeing glitches on your monitor
• No async support

Known issues

• The (optional) embedded graphics driver doesn't draw correctly in combination with the semi-double buffering mode. See example semi_double_buffered.rs

Examples

You can find some examples in the directory rp-cvideo-examples in the root of the repository.

Hardware

Two digital pins of the MCU are used to generate an analog signal containing 3 discrete voltage levels: 0.0, 0.3 and 1.0 volt, respectively meaning sync, black and white. The easiest way to make this work is with the following example schematic:

┌─────────────────┐ ┌──────┐
│        GP0(sync)├─┤ 560Ω ├───┐
│ RP              │ └──────┘   │
│ Pico            │ ┌──────┐   │
│       GP1(video)├─┤ 220Ω ├───┴──► composite
│                 │ └──────┘        video
│                 │                 plug
│              GND├───────────────►
└─────────────────┘

Note These resistor values are for 3.2v digital pins!

Thanks

• Thanks to the rp-rs team for their excellent work that makes this library possible
• Thanks for batsocks for his/hers great reference on the composite video signal

Demo video

A video of the matrix example running on an old green phosphor monitor