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kIOUSBLinkErr
kIOUSBLinkErr reports a USB link or transaction condition at the host-controller or bus layer. Diagnose the transfer path first; the value does not by itself identify an application- or class-driver error.
Where the result is produced
IOKit return values, internal tokens, and service messages share an integer representation but not the same control-flow meaning. Determine whether the API returns the value or delivers it as a message before treating it as failure.
Evidence to preserve
| Capture | Diagnostic value |
|---|---|
| Controller, port path, device address, speed, endpoint, transfer type, completion code, and bus generation. | Identifies the concrete object and operation associated with the result. |
| Numeric IOReturn/message value decoded with the matching SDK header. | Separates an argument or lifecycle state from a failure reported by the underlying provider. |
| Registry generation and first provider/client event before the result. | Correlates the link failure with the registry generation and provider event that immediately preceded it. |
| Known-good device or service state on the same macOS/driver build. | Shows whether the observed value is the primary result or a translated summary. |
A controlled diagnostic sequence
- Move the device to a known-good port/controller with the same cable and request.
- Change one topology or lifecycle condition while keeping the request payload fixed.
- Verify cleanup and object lifetime after the controlled operation.
Correction and proof
Targeted correction. Repair signal, cable, power, hub, controller, or device link behavior before changing application protocol data.
Acceptance criterion. The transfer completes on the original supported topology and repeated reconnects do not reproduce link failures.
Technical references
- Apple XNU: IOReturn definitions — defines the status namespace used.
- Apple: IOKit documentation — documents the API or lifecycle boundary behind it.
- Apple OSS: XNU source — provides ABI, implementation, or protocol context.
- Apple XNU: USB definitions — supports the portability and verification limits.
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