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This commit adds a new parameter to the PIO program decorator, to indicate an explicit program origin in the PIO memory area. There was no possibility to pass an origin position in the PIO constructor, and that would create some problems for PIO programs that use computed jump offsets. By default the state machine program loader does not guarantee a specific start position inside the PIO memory block, which makes things unpredictable for jump tables. Now the decorator allows for an `origin` parameter that takes an integer containing the required offset in PIO memory. Without that parameter behaviour is unchanged. An example showing the usage of this parameter is supplied, `examples/rp2/pio_quadencoder.py`. That is a direct port from `quadrature_encoder.pio` in the Raspberry Pi Pico samples repository into MicroPython's own PIO assembler. Relevant documentation was also updated to keep track of the new decorator signature. Signed-off-by: Alessandro Gatti <a.gatti@frob.it>
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Summary
This PR adds a new parameter to the PIO program decorator, to indicate an explicit program origin in the PIO memory area.
There was no possibility to pass an origin position in the PIO constructor, and that would create some problems for PIO programs that use computed jump offsets. By default the state machine program loader does not guarantee a specific start position inside the PIO memory block, which makes things unpredictable for jump tables.
Now the decorator allows for an
originparameter that takes an integer containing the required offset in PIO memory. Without that parameter behaviour is unchanged.An example showing the usage of this parameter is supplied,
examples/rp2/pio_quadencoder.py. That is a direct port fromquadrature_encoder.pioin the Raspberry Pi Pico samples repository into MicroPython's own PIO assembler.Relevant documentation was also updated to keep track of the new decorator signature.
This closes #11531.
Testing
Although I don't have an encoder available (who knows where the rotary switches went...), the clock frequency is high enough that when running the example code on a RP2040 shorting either pin 16 or pin 17 to ground triggers an increment/decrement response, demonstrating that the PIO program origin was actually picked up correctly (plus you can debug your own way through and see the value coming out :)).
Trade-offs and Alternatives
Size increase is minimal, but this might probably be the least amount of code needed to pull this off.
There are a few PRs that are supposed to improve the state of things w.r.t. PIO, but none of those actually implement origin support. If somebody else with a more complete PR wants to take these changes in to merge with theirs, that's fine by me.
Generative AI
I did not use generative AI tools when creating this PR.