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cpu/sam0_common: Implement time-sharing of SERCOMs #21029

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cpu/sam0_common: Implement time-sharing of SERCOMs #21029

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Commits on Nov 27, 2024

  1. cpu/sam0_common: implement SERCOM time-sharing 

    This adds a `periph_sercom` feature and implementation which
`periph_i2c`, `periph_uart`, and `periph_spi` are implemented on top.
This allows for sharing a single SERCOM instance to provide multiple
serial interfaces (in round-robin time-sharing fashion).

Note: In practice, a SERCOM can often not be shared if it needs to
      provide an UART.

Background:

While code using the I2C/SPI APIs is already optimized to share the
peripheral with `i2c_acquire()`/`spi_acquire()` and
`i2c_release()`/`spi_release()`, UARTs are typically not shared and most
users will not call `uart_poweron()` and `uart_poweroff()` to only have
the SERCOM in UART mode when actually needed. Worse: For many use cases
(such as stdin), the UART will need to be constantly running, as
receiving data happens asynchronously at unpredictable points in time.
    @maribu
    maribu committed Nov 27, 2024
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  2. boards/adafruit-metro-m4-express: make use of SERCOM sharing 

    Now that time-sharing SERCOMs is possible, we can provide the SPI on
D11/D12/D13 (backed by SERCOM3) also when the UART on D0/D1 (also backed
by SERCOM3) is used.
    @maribu
    maribu committed Nov 27, 2024
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  3. boards: fix whitespace style issues 

    This adds the space missing after the comma in `GPIO_PORT(<port>,<pin>`
at multiple places
    @maribu
    maribu committed Nov 27, 2024
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