Analog Devices ADSP-BF53x Blackfin, Reference

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Interrupt Processing
4-50 ADSP-BF53x/BF56x Blackfin Processor Programming Reference
Software Interrupts
Software cannot set bits of the
ILAT
register directly, as writes to
ILAT
cause write-1-to-clear (W1C) operation. Instead, use the
RAISE
instruction
to set individual
ILAT
bits by software. It safely sets any of the
ILAT
bits
without affecting the rest of the register.
RAISE 1; /* fire reset interrupt request */
The
RAISE
instruction must not be used to fire emulation events or excep-
tions, which are managed by the related
EMUEXCPT
and
EXCPT
instructions.
For details, see Chapter 16, “External Event Management.”
Often, the
RAISE
instruction is executed in interrupt service routines to
degrade the interrupt priority. This enables less urgent parts of the service
routine to be interrupted even by low priority interrupts.
isr7: /* service routine for IVG7 */
...
/* execute high priority instructions here */
/* handshake with signalling peripheral */
RAISE 14;
RTI;
isr7.end:
isr14: /* service routine for IVG14 */
...
/* further process event initiated by IVG7 */
RTI;
isr14.end:
The example above may read data from any receiving interface, post it to a
queue, and let the lower priority service routine process the queue after
the
isr7
routine returns. Since
IVG15
is used for normal program execu-
tion in non-multi-tasking system,
IVG14
is often dedicated to software
interrupt purposes.