Interrupt Functions

The following functions are available to manage RTX interrupt services.

Attaching Functions

RtAttachInterrupt can attach an Interrupt Service Thread (IST) and/or an Interrupt Service Routine (ISR) to a specified interrupt. Interrupts may be either line-based or message-based (MSI/MSI-X). You can also share interrupts exclusively attached within the RTSS environment with this call. Use RtAttachInterrupt when attaching an RTSS process to an interrupt.
RtAttachInterruptVectorEx can attach an Interrupt Service Thread (IST) and/or an Interrupt Service Routine (ISR) to a specified interrupt. You can also share interrupts exclusively attached within either the RTSS or Win32 environments (but not both) with this call. Use RtAttachInterruptVectorEx when attaching a Win32 process to an interrupt.
RtAttachInterruptVector attaches an Interrupt Service Thread (IST) to a specified interrupt. You can use RtAttachInterruptVector when attaching a Win32 process to an interrupt, however, RtAttachInterruptVectorEx contains more functionality and is preferable to RtAttachInterruptVector when attaching Win32 processes.

Releasing Functions

RtReleaseInterrupt releases an interrupt previously attached with RtAttachInterrupt. Like RtAttachInterrupt, RTReleaseInterrupt is only supported in the RTSS environment.
RtReleaseInterruptVector releases an interrupt previously attached with RtAttachInterruptVectorEx or RtAttachInterruptVector. This API can be called in RTSS or Windows environments.

Other Functions

RtQueryPciMsiCapability allows a user to query a PCI device and determine if the device has MSI or MSI-X capability. RtQueryPciMsiCapability is only supported in the RTSS environment.
RtDisableInterrupts, under the Win32 environment, disables interrupt handling for all interrupts attached to a process. In the RTSS environment, all interrupts are disabled at the processor level.
RtEnableInterrupts enables all interrupts disabled by RtDisableInterrupts.

Programming Considerations

General Programming Considerations

As with any thread, an interrupt thread can be preempted at any time by a thread that runs at a higher thread priority level.
In dedicated environments, IRQ affinity is set at attach time.
Time slicing effects the execution of ISTs if there is a time quantum set for the IST.
Interrupt processing can be disabled for the set of interrupts attached to the RTX process by raising the thread priority level of the currently executing thread. The level must be higher than all of the thread priority levels specified for the RTSS Interrupt Service Threads (ISTs). An interrupt handler that signals an object may satisfy the wait conditions of a higher priority thread. Resuming the higher priority thread will delay the completion of the interrupt handler and delay the time at which the interrupt source will be unmasked. High priority threads never mask timer interrupts; thus, the timer interrupt is effectively the highest priority interrupt. To mask timer interrupts, use RtDisableInterrupts.

Win32 Environment Programming Considerations

All processing in the RTSS environment takes priority over all processing in the Win32 environment. Therefore, any time-critical interrupt processing that must be accomplished should be done with a handler running an RTSS process, rather than a Win32 process. In the Win32 environment, the Windows scheduler services RTX interrupt threads. This can lead to non-deterministic scheduling latencies for the handling thread to receive and process the interrupt.

Also, remember to use RtAttachInterruptVectorEx or RtAttachInterruptVector when attaching Win32 processes. RtAttachInterrupt is not supported in the Win32 environment.

Examples

For an example of using RtAttachInterrupt, see the IntelPro1000 topic.

For an example of using RtAttachInterruptVector, see the Interrupt Management and Port I/O Calls Programming Example topic.