| Debugging Tools for Windows |
The IRQL_UNEXPECTED_VALUE bug check has a value of 0x000000C8. This indicates that the processor's IRQL is not what it should be at this time.
The following parameters are displayed on the blue screen.
| Parameter | Description |
|---|---|
| 1 | The value of the following bit computation: (Current IRQL << 16) | (Expected IRQL << 8) | UniqueValue |
| 2 | Zero, or APC->KernelRoutine |
| 3 | Zero, or APC |
| 4 | Zero, or APC->NormalRoutine |
You can determine "UniqueValue" by computing (Parameter 1 AND 0xFF). If "UniqueValue" is either zero or one, Parameter 2, Parameter 3, and Parameter 4 will equal the indicated APC pointers. Otherwise, these parameters will equal zero.
This error is usually caused by a device driver or another lower-level program that changed the IRQL for some period and did not restore the original IRQL at the end of that period. For example, the routine may have acquired a spin lock and failed to release it.