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kIOUSBTransactionTimeout
A timeout does not identify the failing layer
kIOUSBTransactionTimeout says that the transaction reached its timeout before normal completion was reported. It is distinct from kIOUSBPipeStalled, which identifies a halted endpoint, and from kIOUSBPortWasSuspended, which identifies power-state interruption. The same timeout can result from a device that did not respond, an endpoint waiting for data, a busy bus path, a wrong protocol sequence, or an application timeout that is shorter than the valid operation.
The return code alone does not define the state of the higher-level command. Completion interfaces expose request-specific information such as remaining buffer length, and a device protocol may have processed part of a command before the host gave up waiting. A blind retry can duplicate non-idempotent work.
Useful evidence
- Log endpoint address, direction, transfer type, requested length, timeout value, remaining length, and the active configuration and alternate setting.
- Preserve the preceding control or bulk exchanges and any device-side status, rather than relying only on the timeout code.
- Compare the configured timeout with the documented timing of the specific device operation.
- Choose retry, abort, or re-enumeration from the device protocol and the operation's idempotence, not from the timeout code alone.
References
- Apple: IOUSBFamily error codes
- IOUSBFamily source: timeout handling in pipe I/O
- libusb: transfer completion states and timeout handling
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