cpu/sam0_common: Implement time-sharing of SERCOMs

[maribu]

Contribution description

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.

Testing procedure

make BOARD=adafruit-metro-m4-express flash term -C tests/periph/selftest_shield

2024-11-21 20:29:42,410 # ALL TESTS SUCCEEDED

2024-11-21 20:29:42,395 # main(): This is RIOT! (Version: 2025.01-devel-156-g1baf0-cpu/sam0_common/periph_sercom)
2024-11-21 20:29:42,396 # self-testing peripheral drivers
2024-11-21 20:29:42,396 # ===============================
2024-11-21 20:29:42,396 # Starting test for GPIO at tests/periph/selftest_shield/main.c:350
2024-11-21 20:29:42,396 # [OK]
2024-11-21 20:29:42,397 # Starting test for GPIO at tests/periph/selftest_shield/main.c:372
2024-11-21 20:29:42,397 # [OK]
2024-11-21 20:29:42,397 # Starting test for GPIO at tests/periph/selftest_shield/main.c:402
2024-11-21 20:29:42,397 # [OK]
2024-11-21 20:29:42,397 # Starting test for GPIO at tests/periph/selftest_shield/main.c:432
2024-11-21 20:29:42,397 # (skipped)
2024-11-21 20:29:42,398 # Starting test for GPIO at tests/periph/selftest_shield/main.c:458
2024-11-21 20:29:42,398 # (skipped)
2024-11-21 20:29:42,398 # Starting test for GPIO-IRQ at tests/periph/selftest_shield/main.c:505
2024-11-21 20:29:42,398 # [OK]
2024-11-21 20:29:42,399 # Starting test for GPIO-IRQ at tests/periph/selftest_shield/main.c:571
2024-11-21 20:29:42,399 # [OK]
2024-11-21 20:29:42,399 # Starting test for GPIO-IRQ at tests/periph/selftest_shield/main.c:637
2024-11-21 20:29:42,399 # [OK]
2024-11-21 20:29:42,399 # Starting test for I2C at tests/periph/selftest_shield/main.c:711
2024-11-21 20:29:42,399 # [OK]
2024-11-21 20:29:42,400 # Starting test for UART at tests/periph/selftest_shield/main.c:806
2024-11-21 20:29:42,400 # [OK]
2024-11-21 20:29:42,400 # Starting test for UART at tests/periph/selftest_shield/main.c:815
2024-11-21 20:29:42,400 # [OK]
2024-11-21 20:29:42,400 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,401 # [OK]
2024-11-21 20:29:42,401 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,401 # [OK]
2024-11-21 20:29:42,401 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,401 # [OK]
2024-11-21 20:29:42,402 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,402 # [OK]
2024-11-21 20:29:42,402 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,402 # [OK]
2024-11-21 20:29:42,402 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,402 # [OK]
2024-11-21 20:29:42,403 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,403 # [OK]
2024-11-21 20:29:42,403 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,403 # [OK]
2024-11-21 20:29:42,404 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,404 # [OK]
2024-11-21 20:29:42,404 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,404 # [OK]
2024-11-21 20:29:42,404 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,405 # [OK]
2024-11-21 20:29:42,405 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,405 # [OK]
2024-11-21 20:29:42,405 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,405 # [OK]
2024-11-21 20:29:42,406 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,406 # [OK]
2024-11-21 20:29:42,406 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,406 # [OK]
2024-11-21 20:29:42,406 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,406 # [OK]
2024-11-21 20:29:42,407 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,407 # [OK]
2024-11-21 20:29:42,407 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,407 # [OK]
2024-11-21 20:29:42,408 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,408 # [OK]
2024-11-21 20:29:42,408 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,408 # [OK]
2024-11-21 20:29:42,408 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,408 # [OK]
2024-11-21 20:29:42,409 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,409 # [OK]
2024-11-21 20:29:42,409 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,409 # [OK]
2024-11-21 20:29:42,409 # Starting test for SPI at tests/periph/selftest_shield/main.c:858
2024-11-21 20:29:42,409 # [OK]
2024-11-21 20:29:42,410 # Starting test for ADC at tests/periph/selftest_shield/main.c:1072
2024-11-21 20:29:42,410 # [OK]
2024-11-21 20:29:42,410 # 
2024-11-21 20:29:42,410 # 
2024-11-21 20:29:42,410 # ALL TESTS SUCCEEDED
2024-11-21 20:29:42,410 # { "threads": [{ "name": "main", "stack_size": 1536, "stack_used": 572}]}

Issues/PRs references

None

[riot-ci]

Murdock results

✔️ PASSED

bd365b1 boards: fix whitespace style issues

Success	Failures	Total	Runtime
10248	0	10249	16m:54s

Artifacts

• Documentation preview

[kfessel]

please reduce static noise

there are multiple warnings like

Check warning on line 122 in boards/arduino-nano-33-iot/include/periph_conf.h
GitHub Actions / static-tests

comma should be followed by whitespace

- .rx_pin   = GPIO_PIN(PB,23),
+ .rx_pin   = GPIO_PIN(PB, 23),

[kfessel]

boards/samd20-xpro/include/periph_conf.h
and
boards/samd21-xpro/include/periph_conf.h

also miss white space ( i don't know why these messages are not brought up at once but trickel after every commit)

the static test also don't like regular form past tens of irregular "reset"

[kfessel]

seems like vera++ produced that noise, i reduced that list to once per file and warning

boards/samd20-xpro/include/periph_conf.h:141: warning: comma should be followed by whitespace
boards/samd21-xpro/include/periph_conf.h:143: warning: comma should be followed by whitespace
boards/samr21-xpro/include/periph_conf.h:165: warning: comma should be followed by whitespace
boards/samr30-xpro/include/periph_conf.h:63: warning: comma should be followed by whitespace
boards/sodaq-autonomo/include/periph_conf.h:45: warning: comma should be followed by whitespace
boards/sodaq-explorer/include/periph_conf.h:41: warning: comma should be followed by whitespace
boards/sodaq-one/include/periph_conf.h:44: warning: comma should be followed by whitespace
boards/sodaq-sara-aff/include/periph_conf.h:61: warning: comma should be followed by whitespace
cpu/cortexm_common/include/cpu.h:95: warning: line is longer than 100 characters
cpu/cortexm_common/include/cpu.h:[24](https://github.com/RIOT-OS/RIOT/actions/runs/12050475159/job/33599437291?pr=21029#step:6:31)4: warning: horizontal tab used
cpu/sam0_common/periph/i2c.c:209: warning: comma should not be preceded by whitespace
cpu/sam0_common/periph/i2c.c:308: warning: full block {} expected in the control structure
cpu/samd21/include/periph_cpu.h:55: warning: too many consecutive empty lines
cpu/saml1x/include/periph_cpu.h:139: warning: line is longer than 100 characters
cpu/saml21/include/periph_cpu.h:198: warning: line is longer than 100 characters
pkg/openwsn/include/openwsn_log.h:72: warning: full block {} expected in the control structure

[maribu]

vera++ should now be happy