What does macOS kernel return 0xE0008106 (kIOFireWireIsochBandwidthNotAvailable) mean?

 
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kIOFireWireInvalidResponseLength kIOFWMessageServiceIsRequestingClose

kIOFireWireIsochBandwidthNotAvailable

Bandwidth is reserved before real-time traffic starts

kIOFireWireIsochBandwidthNotAvailable means that the isochronous resource manager could not reserve the requested bandwidth for the stream. FireWire requires a node to obtain both a channel and a bandwidth reservation before it begins isochronous sending or receiving. The reservation protects the timing budget for real-time traffic; it is not an application buffer size and is not repaired by resubmitting the same transfer.

The resource manager tracks a bus-wide availability quantity. IEEE 1394 material describes a dedicated bandwidth-available register, while the Linux FireWire API reports channel and bandwidth allocation separately. Consequently, this status differs from kIOFireWireNoChannels: a channel may be obtainable even though the requested time budget is not.

Diagnose the reservation, not just the device

  • Record the requested stream parameters that determine per-cycle demand, including payload size, packet rate, speed, and any audio or video mode that changes the isochronous load.
  • List other isochronous streams on the same bus and retain the resource-manager result. A device attached through another connector can still compete when it shares the same FireWire bus.
  • Lower bandwidth only through a documented stream mode that changes the actual FireWire reservation. Reducing an unrelated application queue does not release bus bandwidth.
  • Handle bus resets as allocation events: reservations can be recovered automatically, but recovery can fail and the application must check the resulting channel and bandwidth state before restarting media flow.

References

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