USB bulk endpoint stalls during firmware transfer
A sample report for a device that enumerates but stalls or times out during a bulk endpoint transaction.
Evidence handoff preview
Failure boundary Enumeration succeeded, but the failure occurs after host traffic moves to the bulk endpoint used by the firmware transfer.
Raw evidence excerpt
Device configured; bulk OUT starts; transfer status changes to stall/timeout; no matching successful completion for the requested payload window.Evidence screenshots
Evidence table
| Layer | Finding | Implication |
|---|---|---|
| Enumeration | The device configured successfully before bulk transfer traffic began. | The failure is not basic USB visibility or driver installation. |
| Bulk endpoint | The failing status appears on the endpoint used for the transfer payload. | Firmware transfer handling, endpoint buffering, or host timeout settings should be reviewed. |
| Payload window | The captured payload context narrows the failure to a repeatable transaction window. | The case can be reproduced and compared across firmware builds. |
Recommended fix
- Retest with the same payload size on a known-good firmware build.
- Check endpoint max packet size, buffering, NAK/stall handling, and host timeout policy.
- Save the .bscope session and attach the report to the firmware regression ticket.