## Input/Output Device Driver Reference

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### Parallel Port IRQ Timeout Processing

The parallel port device driver sets a 120-second timer after receiving a Write request and sending the first byte to the parallel port. If a hardware interrupt is not generated after 120 seconds, the timer expires and a timeout occurs.

There are two different mechanisms for processing timeouts:

If infinite retry is enabled, the parallel port device driver does not terminate the request and indefinitely continues to try to send the data to the printer.

If infinite retry is disabled, the parallel port device driver terminates the Write request, returning the number of actual bytes sent to the device.

When a monitor is registered, infinite retry is always enabled. The parallel port device driver sends a status monitor packet through the data chain (Index=1) when a timeout error occurs. This activity alerts all monitors of the error.

If a hardware interrupt does occur, the parallel port device driver resets the timer to 120 seconds and sends the next byte to the device. This activity continues until all data has been sent to the device. Once the parallel port device driver determines that all characters have been sent, it turns the timer OFF.