Interrupt

Hardware devices need to notify the system that something requires attention.

THe disk drive notifies completion by requesting an interrupt. → connect to an Interrupt Controller hardware that then sends the request to a processor for handling.

Interrupt Service Routine (ISR)

Routine/function that executed when a interrupt sent to Interrup controller hardware which sends the request to a processor.

Interrupt Request Level (IRQL)

Priority for hardware interrupt. A hardware may send a request with IRQL 5 , a processor if has a lower IRQL will save it’s current state and then execute the ISR.

NOTE: Mask ISR is executed by the same thread.

NOTE: Context switching is no tpossible when the IRQL of interrupted processoris 2 or higher.

IRQL Levels

• PASSIVE_LEVEL in WDK (0) - Normal User mode/kernel mode
• APC_LEVEL (1) - Used for kernel APCs.
• DISPATCH_LEVEL (2) - scheduler cannot wakeup on this CPU. Paged memory access is not allowed.
• DEVICE IRQL (3-11)
• HIGHEST LEVEL (15)

Interupts.exe