cpu/sam0_common: Implement time-sharing of SERCOMs #21029
Draft
+1,222
−985
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
github-actions
bot
added
Platform: ARM
maribu
added
the
CI: ready for build
maribu
changed the title
benpicco
reviewed
Nov 21, 2024
| @@ -104,7 +104,7 @@ static const adc_conf_chan_t adc_channels[] = { | |||
| */ | |||
| static const i2c_conf_t i2c_config[] = { | |||
| { | |||
| .dev = &(SERCOM3->I2CM), | |||
| .sercom = 3, | |||
There was a problem hiding this comment.
We already have sercom_id(), that would be less invasive
There was a problem hiding this comment.
This is a bit more efficient, though. And the conversion is pretty straight-forward.
But I can change this to use sercom_id(), if you prefer compatibility with out-of-tree boards.
There was a problem hiding this comment.
Whats the verdict? Use uint8_t sercom and touch all boards for better efficiency, or stick with void *dev for backward compatibility with out-of-tree boards?
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.
Now that sharing SERCOMs is implemented, we can make use of that :) A warning is emitted if this is actually done, as sharing with UART is often not working as expected.
Calling `uart_poweroff()` when done with the UART test allows sharing the underlying hardware e.g. to provide other peripheral interfaces. One example of this would be the SERCOM3 on the Adafruit Metro M4 Express that is used to provide UART on D1/D0 and SPI on D11/D12/D13.
We cannot use the D0/D1 UART if it is also used for STDIO. However, the logic did not take into account whether `stdio_uart` was used at all. This fixes the issue.
The M4 Express does now have an I2C and an UART compatible with Arduino Shields, so we can expose them.
maribu
force-pushed
the
cpu/sam0_common/periph_sercom
branch
from
1baf069
to
f9c952d
Compare
kfessel
reviewed
Nov 22, 2024
kfessel
reviewed
Nov 22, 2024
kfessel
reviewed
Nov 22, 2024
Also detect TTY of bootloader with `MOST_RECENT_PORT=1`.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Contribution description
This adds a
periph_sercomfeature and implementation whichperiph_i2c,periph_uart, andperiph_spiare 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()andi2c_release()/spi_release(), UARTs are typically not shared and most users will not calluart_poweron()anduart_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_shield2024-11-21 20:29:42,410 # ALL TESTS SUCCEEDEDIssues/PRs references
None