Getting Started with QNX Neutrino - QNX Software Systems

Writing interrupt handlers
© 2009, QNX Software Systems GmbH & Co. KG.
The flags parameter
The last parameter, flags, controls all kinds of things:
_NTO_INTR_FLAGS_END
Indicates that this handler should go after other handlers that may be attached to
the same interrupt source.
_NTO_INTR_FLAGS_PROCESS
Indicates that this handler is associated with the process rather than the thread.
What this boils down to is that if you specify this flag, the interrupt handler will
be automatically dissociated from the interrupt source when the process exits. If
you don’t specify this flag, the interrupt handler will be dissociated from the
interrupt source when the thread that created the association in the first place
exits.
_NTO_INTR_FLAGS_TRK_MSK
The interrupt service routine
Using InterruptAttach()
Indicates that the kernel should track the number of times the interrupt has been
masked. This causes a little more work for the kernel, but is required to ensure
an orderly unmasking of the interrupt source should the process or thread exit.
Let’s look at the ISR itself. In the first example, we’ll look at using the
InterruptAttach() function. Then, we’ll see the exact same thing, except with
InterruptAttachEvent().
Continuing our example, here’s the ISR intHandler(). It looks at the 8250 serial port
chip that we assume is attached to HW_SERIAL_IRQ:
/*
* int1.c
*/
#include
#include
#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
volatile int serial_msr; // saved contents of Modem Status Reg
volatile int serial_rx; // saved contents of RX register
volatile int serial_lsr; // saved contents of Line Status Reg
static int base_reg = 0x2f8;
178 Chapter 4 • Interrupts April 30, 2009