Getting Started with QNX Neutrino - QNX Software Systems

© 2009, QNX Software Systems GmbH & Co. KG. Writing interrupt handlers
When the Ethernet ISR finished clearing the source of the interrupt (step 5), the
interrupt line is still asserted, thanks to the SCSI hardware device. However, the PIC,
being programmed in edge-sensitive mode, is looking for an inactive-to-active
transition (on the composite line) before recognizing another interrupt. That isn’t
going to happen because the kernel has already called both interrupt service routines
and is now waiting for another interrupt from the PIC.
In this case, a level-sensitive solution would be appropriate because when the Ethernet
ISR finishes and the kernel issues the EOI to the PIC, the PIC would pick up the fact
that an interrupt is still active on the bus and re-interrupt the kernel. The kernel would
then run through the chain of ISRs, and this time the SCSI driver would get a chance
to run and clear the source of the interrupt.
The selection of edge-sensitive versus level-sensitive is something that will depend on
the hardware and the startup code. Some hardware will support only one or the other;
hardware that supports either mode will be programmed by the startup code to one or
the other. You’ll have to consult the BSP (Board Support Package) documentation that
came with your system to get a definitive answer.
Writing interrupt handlers
Attaching an interrupt handler
Let’s see how to set up interrupt handlers — the calls, the characteristics, and some
strategies.
To attach to an interrupt source, you’d use either InterruptAttach() or
InterruptAttachEvent().
#include
int
InterruptAttachEvent (int intr,
const struct sigevent *event,
unsigned flags);
int
InterruptAttach (int intr,
const struct sigevent *
(*handler) (void *area, int id),
const void *area,
int size,
unsigned flags);
The intr argument specifies which interrupt you wish to attach the specified handler to.
The values passed are defined by the startup code that initialized the PIC (amongst
other things) just before Neutrino was started. (There’s more information on the
startup code in your Neutrino documentation; look in the Utilities Reference, under
startup-*; e.g., startup-p5064.)
At this point, the two functions InterruptAttach() and InterruptAttachEvent() differ.
Let’s look at InterruptAttachEvent() as it’s simpler, first. Then we’ll come back to
InterruptAttach().
April 30, 2009 Chapter 4 • Interrupts 175