For sufficiently large cyw43 PIO SPI transfers, sleep via async_context before entering busy wait. #2344

2025-03-10T12:52:49-05:00

esky-software commented

2025-03-10 12:52:49 -05:00

(Migrated from github.com)

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.

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.

lurch (Migrated from github.com) reviewed

2025-03-13 05:36:27 -05:00

src/rp2_common/pico_cyw43_driver/cyw43_bus_pio_spi.c

					
				@ -55,2 +55,4 @@

				#endif

				// PICO_CONFIG: CYW43_PIO_SLEEP_MIN_US, For PIO SPI transfers longer than this (in microseconds), sleep via async_context before entering busy wait, type=int, default=disabled, group=pico_cyw43_driver

				#if CYW43_PIO_SLEEP_MIN_US

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? 😉 )

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? :wink: )

esky-software (Migrated from github.com) reviewed

2025-03-13 11:58:15 -05:00

src/rp2_common/pico_cyw43_driver/cyw43_bus_pio_spi.c

					
				@ -55,2 +55,4 @@

				#endif

				// PICO_CONFIG: CYW43_PIO_SLEEP_MIN_US, For PIO SPI transfers longer than this (in microseconds), sleep via async_context before entering busy wait, type=int, default=disabled, group=pico_cyw43_driver

				#if CYW43_PIO_SLEEP_MIN_US

The default value is 0/undefined, which preserves the present functionality.

kilograham (Migrated from github.com) reviewed

2025-04-04 13:29:45 -05:00

src/rp2_common/pico_cyw43_driver/cyw43_bus_pio_spi.c

					
				@ -55,2 +55,4 @@

				#endif

				// PICO_CONFIG: CYW43_PIO_SLEEP_MIN_US, For PIO SPI transfers longer than this (in microseconds), sleep via async_context before entering busy wait, type=int, default=disabled, group=pico_cyw43_driver

				#if CYW43_PIO_SLEEP_MIN_US

it should still have a PICO_CONFIG so people know it exists (it will show up in the docs)

esky-software (Migrated from github.com) reviewed

2025-04-10 07:12:09 -05:00

src/rp2_common/pico_cyw43_driver/cyw43_bus_pio_spi.c

					
				@ -55,2 +55,4 @@

				#endif

				// PICO_CONFIG: CYW43_PIO_SLEEP_MIN_US, For PIO SPI transfers longer than this (in microseconds), sleep via async_context before entering busy wait, type=int, default=disabled, group=pico_cyw43_driver

				#if CYW43_PIO_SLEEP_MIN_US

Added.

peterharperuk (Migrated from github.com) reviewed

2025-05-08 11:20:25 -05:00

peterharperuk (Migrated from github.com) left a comment

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Seem like a good change and a good idea.

lurch (Migrated from github.com) reviewed

2025-05-08 11:40:09 -05:00

src/rp2_common/pico_cyw43_driver/cyw43_bus_pio_spi.c

					
				@ -54,6 +54,18 @@ void cyw43_set_pio_clkdiv_int_frac8(uint32_t clock_div_int, uint8_t clock_div_fr

				}

Could you add type=int, in here (just before the default) please? (apologies for the late feedback)

Could you add `type=int, ` in here (just before the `default`) please? (apologies for the late feedback)

esky-software (Migrated from github.com) reviewed

2025-05-08 12:01:17 -05:00

src/rp2_common/pico_cyw43_driver/cyw43_bus_pio_spi.c

					
				@ -54,6 +54,18 @@ void cyw43_set_pio_clkdiv_int_frac8(uint32_t clock_div_int, uint8_t clock_div_fr

				}

Done.

esky-software commented

2025-05-30 05:13:57 -05:00

(Migrated from github.com)

Not sure why this shows as 'esky software dismissed peterharperuk's stale review...' with my update.
Did I do something wrongly?

Not sure why this shows as 'esky software dismissed peterharperuk's stale review...' with my update. Did I do something wrongly?

peterharperuk commented

2025-05-30 05:39:33 -05:00

(Migrated from github.com)

It's a mystery - don't worry about it.

peterharperuk (Migrated from github.com) approved these changes

2025-05-30 10:41:13 -05:00

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