new sample modules for rp2: ieee488, DMA/PIO extended neopixels, and a compressing bus analyzer

[mendenm]

I am finally getting around to posting some of the useful bits of code I have written in the past year or so. They are on github, at:
https://github.com/mendenm/rp2_micropython_tricks

The modules are:

1. data_compressing_analyzer, which is a PIO-based bus analyzer that transmits back only changes in pins being monitored, with timestamps. Thus, it can operate at high time resolution (clock frequency / 11, at best), but not overflow memory with idle, identical words waiting for the next transition

2. ieee488, an implementation of the ieee-488 (GPIB) protocol using the PIO. I have tested this directly wiring a single IEEE-488 power supply to an RP2040, with no intervening components. It violates all kinds of formal bus loading and driving rules, but seems to work fine. The pull-up current from the device seems to not overload the protective diodes in the CPU, so the 5V -> 3.3V mismatch doesn't seem harmful. I wouldn't attach multiple IEEE-488 devices to a single CPU, though, or current limits (both sourcing and sinking) may be exceeded.

3. rp2_neopixel, a greatly extended neopixel driver, using PIOs and DMA, to allow a neopixel string to be dynamically updated with almost no CPU load. It automatically handles 3-color RGB, 4-color RGBW, and single-color (all white) strings. It can automatically multiple-buffer outputs, so you can be writing data to a buffer, which the previous buffer is being transmitted via the DMA channel. This allows a wide variety of asyncio and synchronous approaches to handling long strings (thousands) of neopixels, and allows multiple string to be supported.