rp2/spi: Allow omitting of unused pins #16428
Conversation
The change makes it possible to omit unused SPI pins. This can be achieved by setting a pin as `None`. The commit changes behavior if the constructor method. Previously if a pin was set as `None` the default pin number for this interface has been used. Signed-off-by: Maksim Salau <maksim.salau@gmail.com>
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This is a good feature to have, but we need to check how other ports handle this case (of omitting pins) so the API is the same across all ports. |
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Missed that I had effectively duplicated this here: #16922 In most cases users would be disabling MISO, for the reasons given in my PR, but it's feasible that MISO or MOSI could be disabled for single direction SPI (read a read only device, write a write only device). Not to be confused for half duplex mode. sck though? That's a tough sell! |
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It seems that a similar change was merged today: commit dd7a950. |
I made a HX711 driver once which uses MOSI to create the clock signal of 25-27 clock pulses. So the SPI SCK was not used. But applications are rare, and it this case using GPIO bit banging was better. The only advantage of using SPI was a reliable timing. |
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Thanks for pointing out that similar feature is already in repo. |
Summary
The change makes it possible to omit unused SPI pins.
This can be achieved by setting a pin as
None.Testing
The change as been tested on a custom RP2040 board with only SCK and MOSI used to drive a SPI IC.
Trade-offs and Alternatives
The commit changes behavior if the constructor method.
Previously if a pin was set as
Nonethe default pin number for this interface has been used.