Getting Started with QNX Neutrino - QNX Software Systems

Writing interrupt handlers
© 2009, QNX Software Systems GmbH & Co. KG.
Using InterruptAttachEvent()
With the volatile keyword, we’re telling the compiler not to cache the value of any
of these variables, because they can change at any point during execution.
The next thing we notice is the prototype for the interrupt service routine itself. It’s
marked as const struct sigevent *. This says that the routine intHandler()
returns a struct sigevent pointer. This is standard for all interrupt service
routines.
Finally, notice that the ISR decides if the thread will or won’t be sent an event. Only in
the case of a Modem Status Register (MSR) interrupt do we want the event to be
delivered (the event is identified by the variable event, which was conveniently passed
to the ISR when we attached it). In all other cases, we ignore the interrupt (and update
some global variables). In all cases, however, we clear the source of the interrupt. This
is done by reading the I/O port via in8().
If we were to recode the example above to use InterruptAttachEvent(), it would look
like this:
/*
* part of int2.c
*/
#include
#include
#define HW_SERIAL_IRQ 3
#define REG_RX 0
#define REG_II 2
#define REG_LS 5
#define REG_MS 6
#define IIR_MASK
0x07
#define IIR_MSR
0x00
#define IIR_THE
0x02
#define IIR_RX
0x04
#define IIR_LSR
0x06
#define IIR_MASK
0x07
static int base_reg = 0x2f8;
int
main (int argc, char **argv)
{
int intId; // interrupt id
int iir; // interrupt identification register
int serial_msr; // saved contents of Modem Status Reg
int serial_rx; // saved contents of RX register
int serial_lsr; // saved contents of Line Status Reg
struct sigevent event;
// usual main() setup stuff...
// set up the event
intId = InterruptAttachEvent (HW_SERIAL_IRQ, &event, 0);
for (;;) {
// wait for an interrupt event (could use MsgReceive instead)
180 Chapter 4 • Interrupts April 30, 2009