LP-AM243: AM243x USB device mode: Endpoint stops responding after DFLUSH during IN transfer

Motofumi Kibata

Part Number: LP-AM243

Tool/software:

Hi,

I am using the AM243x in USB device mode, and have encountered an issue related to the use of DFLUSH on a Bulk IN endpoint.

Issue:
If we issue a DFLUSH command to an IN endpoint *while it is in the middle of an IN transfer*, the endpoint stops responding entirely after that point. It no longer returns NAK, STALL, or any response at all to the host.
Steps to reproduce:
1. Start an IN transfer on an endpoint (e.g. EP1 IN).
2. While the transfer is ongoing, set DFLUSH bit for that endpoint. (Sequence equivalent to the epFifoFlush() API)
3. The endpoint becomes unresponsive afterwards — host receives no response.
Question:
- Is this a known issue or hardware limitation of AM243x?
- Is it safe to call DFLUSH during an active IN transfer?
- Are there any recommended recovery methods or workarounds?

I tested repeatedly issuing DMA requests and DFLUSH commands while the relevant EP was not being transferred, and in that case, no issues seemed to occur.
I would appreciate any clarification on the expected behavior of DFLUSH and best practices to avoid this issue.

Best Regards,

10 months ago

0 Tushar Thakur 10 months ago

TI__Guru 64348 points

Hi Motofumi,

Motofumi Kibata said:
If we issue a DFLUSH command to an IN endpoint *while it is in the middle of an IN transfer*, the endpoint stops responding entirely after that point. It no longer returns NAK, STALL, or any response at all to the host.

Can you please tell why are you trying to flush the endpoint in the middle of transfer?

Regards,

Tushar

0 Motofumi Kibata 10 months ago in reply to Tushar Thakur

Prodigy 140 points

Hi Tushar,

Thank you for your reply.

I want to set a timeout for communication requests, but when the timeout occurs, communication may happen simultaneously with DFLUSH, potentially causing DFLUSH to be performed during an ongoing communication.

Best Regards,

Motofumi

0 Tushar Thakur 10 months ago in reply to Motofumi Kibata

TI__Guru 64348 points

Hi Motofumi,

You should not flush the endpoint in middle of transfers. Flushing the endpoint will clears the DRDY bit and stops DMA transfer. This will also flush the endpoint data from on-chip buffers.

You can refer to CUSBDMA_ChannelHandleStall API to stalls the endpoint.

Regards,

Tushar

0 Motofumi Kibata 10 months ago in reply to Tushar Thakur

Prodigy 140 points

Hi Tushar,

Thank you for your reply.

Instead of DFLUSH, I implemented stall -> unstall processing based on CUSBDMA_ChannelHandleStall. However, executing this during communication timing causes the same issue where subsequent communication becomes impossible.

Best Regards,

Motofumi

0 Motofumi Kibata 10 months ago in reply to Motofumi Kibata

Prodigy 140 points

Hi Tushar,

Sorry for asking so many questions in a row.

Tushar Thakur said:
You should not flush the endpoint in middle of transfers.

Is there a way to detect via software that a transfer is in progress?

Best Regards,

Motofumi

0 Tushar Thakur 10 months ago in reply to Motofumi Kibata

TI__Guru 64348 points

Hi Motofumi,

You can refer to the EP_STS.DBUSY[9] bit of the EP_STS register to check the DMA status.

If the bit is set, DMA transfer is going on otherwise DMA is free.

Regards,

Tushar

0 Motofumi Kibata 10 months ago in reply to Tushar Thakur

Prodigy 140 points

Hi Tushar,

I'll check EP_STS.DBUSY. Thank you so much.

Best Regards,

Motofumi

0 Tushar Thakur 10 months ago in reply to Motofumi Kibata

TI__Guru 64348 points

Hi Motofumi,

Thanks for the above confirmation.

Regards,

Tushar

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LP-AM243: AM243x USB device mode: Endpoint stops responding after DFLUSH during IN transfer