HwInterrupt Routine

On entry, a HwInterrupt routine should determine if its HBA actually generated an interrupt. HwInterrupt must return FALSE as soon as possible if it detects a spurious interrupt so the interrupt service routine for the device that generated the interrupt can be called quickly.

Otherwise, a miniport's HwInterrupt routine is generally responsible for completing the I/O operation that caused the interrupt. Depending on the HBA and the design of the miniport, a HwInterrupt routine does some or all of the following:

• Dismisses the interrupt on the HBA
• Notifies (by calling ScsiPortNotification or ScsiPortCompleteRequest) the port driver if the HBA indicates that certain SCSI error conditions occurred during the operation and logging the error (see Error Handling)
• Completing the requested operation that caused the interrupt, such as calling ScsiPortIoMapTransfer if the interrupt came in from a previously selected target TID and LU indicating a readiness to transfer data

When the HwInterrupt routine (or an internal miniport routine) completes an SRB, it calls ScsiPortNotification twice:

1. First, with the NotificationType RequestComplete and the just satisfied request
2. Next, with the NotificationType NextRequest, or with NextLuRequest if the HBA supports tagged queuing or multiple requests per logical unit

For better overall system performance, a miniport's HwInterrupt routine should do only the minimum necessary to process I/O requests. That is, the miniport should be designed to return control from the HwInterrupt routine as quickly as possible, rather than tying up a processor and preventing other drivers from servicing device interrupts.

If interrupt-driven I/O operations take a long time to complete, a miniport driver should have a pair of HwEnableInterruptsCallback and HwDisableInterruptsCallback routines. For example, if a miniport must poll for longer than 50 microseconds doing PIO, its HwInterrupt routine should not retain control of the CPU for the full polling interval in order to complete a requested operation. Instead, its HwInterrupt routine should do the following:

1. Disable interrupts from the HBA.
2. Set up the device extension with any context necessary to complete the operation.
3. Call ScsiPortNotification with a pointer to the device extension, the NotificationType CallEnableInterrupts, and the miniport's HwEnableInterruptsCallback routine, described in HwEnableInterruptsCallback Routine.
4. Return control.

ScsiPortNotification calls the HwEnableInterruptsCallback routine as an DPC.