For sufficiently large cyw43 PIO SPI transfers, sleep via async_context before entering busy wait. #2344
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
…text before entering busy wait.
lurch
reviewed
Mar 13, 2025
| @@ -54,6 +54,17 @@ void cyw43_set_pio_clkdiv_int_frac8(uint32_t clock_div_int, uint8_t clock_div_fr | |||
| } | |||
| #endif | |||
|
|
|||
| #if CYW43_PIO_SLEEP_MIN_US | |||
There was a problem hiding this comment.
Perhaps this should have a // PICO_CONFIG: metadata-comment? See https://github.com/search?q=repo%3Araspberrypi%2Fpico-sdk%20PICO_CONFIG&type=code for other examples. (although I guess that means you probably want to decide on a sensible "default" value for this too? 😉 )
There was a problem hiding this comment.
The default value is 0/undefined, which preserves the present functionality.
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Outdated suggestions cannot be applied.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.
Fixes #2343
The function cyw43_spi_transfer() busy waits on the transfer DMA channel(s), even for large transfers.
This is far from optimal in an RTOS or other asynchronous environment.
We might use DMA interrupts to handle the completion of the transfer, but this would require some restructuring of the driver code.
More simply, we can estimate the duration of the transfer, and if it's larger than a threshold call cyw43_delay_us() to sleep via the async context before starting the busy wait for the end of the transfer.
Define CYW43_PIO_SLEEP_MIN_US as the threshold duration (microseconds) to enable the feature.