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kIOFireWireLastDCLToken
kIOFireWireLastDCLToken is an internal FireWire marker for the final callback or token in a Device Control Language program. It should be interpreted in that program's callback sequence rather than as a general I/O failure.
Operational meaning
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.
Build a reproducible record
| Capture | Diagnostic value |
|---|---|
| DCL program layout, callback order, token value, program generation, channel, and completion trace. | Identifies the concrete object and operation associated with internal final DCL callback token. |
| Numeric IOReturn/message value decoded with the matching SDK header. | Separates argument or lifecycle state from the provider beneath kIOFireWireLastDCLToken. |
| Registry generation and first provider/client event before the result. | Ties the token to one DCL program generation and callback sequence. |
| Known-good device or service state on the same macOS/driver build. | Shows whether kIOFireWireLastDCLToken is the first result or a translated summary. |
Checks that separate the causes
- Run a minimal DCL program with one explicit final callback.
- Change one topology or lifecycle condition while keeping the request payload fixed.
- Verify cleanup and object lifetime after the controlled operation.
Resolution criteria
Targeted correction. Treat the token according to the owning FireWire API and avoid converting it into a generic error path.
Acceptance criterion. The final callback occurs exactly once and program teardown does not consume the token as an error.
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: FireWire family common definitions — supports the portability and verification limits.
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