Getting Started with QNX Neutrino - QNX Software Systems

Writing interrupt handlers
© 2009, QNX Software Systems GmbH & Co. KG.
Attaching with InterruptAttachEvent()
Attaching with InterruptAttach()
The InterruptAttachEvent() function takes two additional arguments: the argument
event, which is a pointer to the struct sigevent that should be delivered, and a
flags parameter. InterruptAttachEvent() tells the kernel that the event should be
returned whenever the interrupt is detected, and that the interrupt level should be
masked off. Note that it’s the kernel that interprets the event and figures out which
thread should be made READY.
With InterruptAttach(), we’re specifying a different set of parameters. The handler
parameter is the address of a function to call. As you can see from the prototype,
handler() returns a struct sigevent, which indicates what kind of an event to
return, and takes two parameters. The first passed parameter is the area, which is
simply the area parameter that’s passed to InterruptAttach() to begin with. The second
parameter, id, is the identification of the interrupt, which is also the return value from
InterruptAttach(). This is used to identify the interrupt and to mask, unmask, lock, or
unlock the interrupt. The fourth parameter to InterruptAttach() is the size, which
indicates how big (in bytes) the data area that you passed in area is. Finally, the flags
parameter is the same as that passed for the InterruptAttachEvent(); we’ll discuss that
shortly.
Now that you’ve attached an interrupt
At this point, you’ve called either InterruptAttachEvent() or InterruptAttach().
Since attaching an interrupt isn’t something you want everyone to be able to do,
Neutrino allows only threads that have “I/O privileges” enabled to do it (see the
ThreadCtl() function in the Neutrino Library Reference). Only threads running from
the root account or that are setuid() to root can obtain “I/O privileges”; hence we’re
effectively limiting this ability to root.
Here’s a code snippet that attaches an ISR to the hardware interrupt vector, which
we’ve identified in our code sample by the constant HW_SERIAL_IRQ:
#include
int interruptID;
const struct sigevent *
intHandler (void *arg, int id)
{
...
}
int
main (int argc, char **argv)
{
...
interruptID = InterruptAttach (HW_SERIAL_IRQ,
intHandler,
&event,
176 Chapter 4 • Interrupts April 30, 2009