RMT: Tentative timing fix/workaround#4637
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This is currently broken due to undocumented timing/ordering constraints of the peripheral, which leads to erroneous behavior when the sclk divider is large (i.e. presuamably when the RMT sclk is slow compared to some bus clock?).
Setting a large RMT SCLK divider breaks the driver in unexpected ways. There's nothing in the documentation hinting at relevant timing constraints (the only thing mentioned are limits on pulse code periods, but that's not the issue here), and the IDF code also doesn't seem to do anything special. It does order some register operations differently, first sets register and only then fills the hardware buffer, and also does more stuff (book keeping, locking, ...). This PR does the following: - match update() calls better to what IDF does (only before tx start, after tx stop, after rx start) - add some delays between configuring channels and actually starting transactions: It appears that adding a delay of about 1 SCLK period fixes all the weirdness. This suggests that some settings take a while to be properly propagated in the peripheral, and failing to provide that time results in weird glitches and hangs. It might be that IDF accidentally sidesteps this due to ordering things as follows (and due to overall doing more including locking, runtime checks, ...): 1. write RMT config registers 2. write data to RMT RAM 3. start tx whereas we switch steps 1 + 2. Thus, switching order might be a way to decrease the required delay, but that would require more research into whether that is really sufficient (e.g. when the data is short and writing it to RAM completes quickly). If there's no overall better way to fix this, maybe one could use cycle counters to just wait the minimal necessary time? In any case, this commit seems to be a minimally-invasive workaround/fix.
Give a more precise error when specifying timings that would make some of the pulses longer than the idle_threshold
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Triggered full HIL run for #4637. Run: https://github.com/esp-rs/esp-hal/actions/runs/20063369980 Status update: ❌ HIL (full) run failed (conclusion: failure). |
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Pull Request Details 📖
Tentative fix for the timing/clock divider issues pointed out in the comments at #3930 (comment). See the commit messages for much more detail.
@ Espressif people: Is there any way for you to figure out what's required to make this work reliably? Whatever the precise issue with large SCLK dividers is, it seems to be entirely undocumented.
cc @kleinesfilmroellchen
Testing
HIL tests on C3.