What does NTSTATUS 0x4000000C (STATUS_SERIAL_COUNTER_TIMEOUT) mean?

STATUS_SERIAL_COUNTER_TIMEOUT

The serial XOFF counter expired before reaching zero

This informational result is the timeout path of IOCTL_SERIAL_XOFF_COUNTER. The driver transmitted XOFF and waited for the configured number of outgoing bytes, but the interval expired before enough writes reduced the counter to zero. The original request is complete even though its byte-count condition was not met.

Investigate whether the application stopped writing, a queue was purged, flow control blocked transmission, or the timeout was shorter than the expected traffic gap. Read and write timeout settings are separate from protocol-level acknowledgements, so increasing them blindly can delay failure detection without fixing stalled communication.

What to inspect

• Capture the requested counter, timeout, queue depth, and transmitted byte count.
• Inspect XON/XOFF and CTS/RTS handshaking state at the time of completion.
• Treat the result as a completed timed operation, not as a still-pending IOCTL.

References

• Microsoft: IOCTL_SERIAL_SET_TIMEOUTS
• Microsoft: IOCTL_SERIAL_GET_COMMSTATUS
• Microsoft Open Specifications: NTSTATUS values