drivers/ws281x: esp32 neopixel driver to set the rmt symbol high/low lengths at init instead of every write

[IsikcanYilmaz]

Contribution description

Minor change to the WS281x driver, specifically the esp32 side.

The ws281x driver for the esp32 uses a hardware module called the RMT, which generates the data signal that the ws281xs expect. The RMT module is supplied with the information about how to generate this signal; for a 1 symbol, how long should the signal be held high, how long should it be low, so on. These 1 and 0 symbol high/low times are recalculated at every RMT write.

This PR does the calculation once at init. Marginal speed up (~10us on my 80 neopixel strip).

If there was a reason for doing it at every write, it was not obvious to me. Please let me know if so.

[IsikcanYilmaz]

Currently the color_rgb_ts get converted to rmt_item32_ts at every write operation. As far as I understand, if we could avoid this conversion at every write, we could have the RMT driver do writes without blocking, and this would yield a better speedup.

Could be done by having ws281x_set_buffer to write to its buffer in the form of a rmt_item32_t instead of color_rgb_t, at least for the esp32 that uses the RMT.

Do the ESP gurus here see anything wrong with this potential solution?

[maribu]

The code change looks good to me. Do you happen to already have tested that this doesn't cause any regressions? (Not that I would expect any from the changes, but better safe than sorry.)

Otherwise I can give the code a spin.

[IsikcanYilmaz]

Do you happen to already have tested that this doesn't cause any regressions?

I'v been running it yes. So far so good.

Otherwise I can give the code a spin.

That would give me more confidence.

[IsikcanYilmaz]

as far as i understand, this change would affect someone's application only if they change clock frequency in run time.

with this change in, should someone do such thing, they would have to deinit and reinit the neopixel driver.

[riot-ci]

Murdock results

✔️ PASSED

53a4a8a drivers/ws281x: esp32 neopixel driver to set the rmt symbol data structures at init instead of every write

Success	Failures	Total	Runtime
10249	0	10249	17m:49s

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