cpu/rpx0xx: implement periph_spi

[fengelhardt]

Contribution description

This PR adds spi functionality to the rpx0xx MCU. It also adds spi configurations to the rpi-pico board's periph_conf.h.

The RP2040 has two SPI blocks of the PL022 type, which are DMA-capable and can be configured in various modes. The SPI clock can be set from clock_periph by means of two clock divisors. With the 125MHz clock of the RPi Pico, only the 100 KHz clock setting can be met exactly. See below.

DMA is not supported by this PR by now. Implementation should be easy once someone can add DMA support.

I have set the default pinout for the RPi Pico as follows in periph_conf.h:

• SPI 0
  • MOSI: pin 3
  • MISO: pin 4
  • CLK: pin 2
• SPI 1
  • MOSI: pin 11
  • MISO: pin 12
  • CLK: pin 10

The pinout might be worth discussing. There might be collisions soon when someone also ad I2C support. The only other option for SPI1 already collides with UART1. Maybe it is better to just leave out SPI1 in the default board config.

Testing procedure

I have run the standard tests in tests/periph_spi on a self-made RP2040-board, which is more or less a Raspberry Pi Pico clone. I have shorted MISO and MOSI with a wire bridge for running this test.

I have also tested spi function with CC1101 wireless transceivers. I was able to communicate successfully between two boards.

Issues/PRs references

Integration of rpx0xx peripherals is tracked in issue #15822

Achieved SPI Clock Speeds

SPI clock is derived from clock_periph by dividing it by two divisors, of which one must be an even number. My current algorithm for finding the divisors is inspired by the method from the Pico SDK, but a bit optimized for speed. With the 125 MHz clock on a RPi Pico, the following SPI clocks are achieved:

• 100 KHz -> exact match
• 400 KHz -> 400641 Hz
• 1 MHz -> 992063 Hz
• 5 MHz -> 4807692 Hz
• 10 MHz -> 10416666 Hz

[dylad]

@fengelhardt Thanks for your contribution !
It already looks really good. I'll try to prepare a quick setup with a sensor or something to give it a try.

[dylad]

I gave this PR a try using a SPI<->SDCARD adapter.
I was able to read my card SD content so it's nice !
@fengelhardt If you have time, could you address @benpicco comments ? It would be good to merge this :)

[fengelhardt]

@fengelhardt If you have time, could you address @benpicco comments ? It would be good to merge this :)

Sure! I was not able to find time yet. But in the coming week maybe.

[fengelhardt]

I think I have addressed everything. Also rebased to current master.

[riot-ci]

Murdock results

✔️ PASSED

7768206 boards/rpi-pico: add spi config

Success	Failures	Total	Runtime
6931	0	6931	10m:19s

Artifacts

• Documentation preview

[maribu]

Cool, only to minor changes and a squash missing, it seems :)

[maribu]

lgtm, please squash.

@benpicco, @dylad: Anything left to do?

[dylad]

I'd like to test it one more time. I should have some time for that tomorrow. But I am all for a rebase/squash 👍

[dylad]

I just give it another shoot. And it still looks good.
Please squash/rebase.

[fengelhardt]

Cool :)

[maribu]

ACK, thx :)

Anyone still wanting changes should speak up now ;)

[maribu]

bors merge

[bors]

Build failed:

• static-tests

[dylad]

Huh bors static-tests complained quite a lot.

[dylad]

bors merge

[bors]

Build succeeded!

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• Murdock
• static-tests
• tools-build-success

[dylad]

Thanks for your contribution @fengelhardt !

[fengelhardt]

Thanks for your contribution @fengelhardt !

Sure! Looking forward to make further contributions. :)