Add documentation to dma_channel_abort regarding errata RP2040-E13 #816

2022-05-09T15:36:44-05:00

kilograham commented

2022-05-09 15:36:44 -05:00

(Migrated from github.com)

See https://github.com/raspberrypi/pico-feedback/issues/224

Note this is a documentation only fix, as dma_channel_abort does not have enough information to efficiently workaround the issue on the callers behalf.

See https://github.com/raspberrypi/pico-feedback/issues/224 Note this is a documentation only fix, as `dma_channel_abort` does not have enough information to efficiently workaround the issue on the callers behalf.

lurch (Migrated from github.com) reviewed

2022-05-09 16:07:36 -05:00

src/rp2_common/hardware_dma/include/hardware/dma.h

					
				@ -473,6 +473,32 @@ static inline void dma_channel_start(uint channel) {

				 *

"an channel completion" -> "a channel completion"

Wren6991 commented

2022-05-10 04:21:48 -05:00

(Migrated from github.com)

I fixed the typo pointed out by @lurch. I also made another change, which might be more contentious, so feel free to back out: poll BUSY rather than ABORT to check for ABORT completion, to guarantee the channel is returned to a quiescent state before the function exits. ABORT clears prematurely due to the erratum (in fact this is the erratum).

The difference in timing is the time taken for the in-flight transfers to drain from the bus FIFOs, which should be a few cycles.

I fixed the typo pointed out by @lurch. I also made another change, which might be more contentious, so feel free to back out: poll BUSY rather than ABORT to check for ABORT completion, to guarantee the channel is returned to a quiescent state before the function exits. ABORT clears prematurely due to the erratum (in fact this *is* the erratum). The difference in timing is the time taken for the in-flight transfers to drain from the bus FIFOs, which should be a few cycles.

Wren6991 (Migrated from github.com) reviewed

2022-05-10 04:22:29 -05:00

Wren6991 (Migrated from github.com) left a comment

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Approval for the docs updates, @kilograham please merge if you are happy with the ABORT -> BUSY polling change

kilograham commented

2022-05-10 16:26:55 -05:00

(Migrated from github.com)

Does the ABORT->BUSY change have an effect on what happens if the channel is disabled?

Wren6991 commented

2022-05-11 04:08:19 -05:00

(Migrated from github.com)

No. BUSY clears once the in-flight and not-yet-issued transfer counts both reach 0. The not-yet-issued count is cleared by the ABORT, and EN=0 does not prevent in-flight transfers from completing.

bruelltuete (Migrated from github.com) reviewed

2022-05-11 15:57:31 -05:00

src/rp2_common/hardware_dma/include/hardware/dma.h

					
				@ -473,6 +473,32 @@ static inline void dma_channel_start(uint channel) {

				 *

Another typo: "to" is twice.

kilograham commented

2022-05-11 19:25:05 -05:00

(Migrated from github.com)

Note I force merged this as the only change after approval was a type in a comment

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gh-raspberrypi/pico-sdk!816

				`@ -473,6 +473,32 @@ static inline void dma_channel_start(uint channel) {`
				`*`

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