ADSP-BF535 Blackfin Processor Hardware Reference
4-53
Program Sequencer
still asserted, at least one pulse is again generated by the SIC. The
Interrupt Status registers indicate the current state of the shared interrupt
sources.
Self-Nesting Mode
The nesting method described in the previous section allows an interrupt
of higher priority to preempt interrupts of lower priority. However, it
does not allow one interrupt to preempt another interrupt of the same pri-
ority, nor does it allow nesting at the same priority level.
When self-nested interrupts are not enabled, general-purpose interrupts
can only preempt general-purpose interrupts of a lower priority (higher
index). For example, when processing interrupt 7, another interrupt 7
request remains pending (
ILAT[7] = 1
), but the interrupt is not serviced
until the current interrupt 7 service routine executes an RTI.
On the other hand, when self-nesting interrupts are enabled, an event
interrupts processing at the same interrupt service level, provided
RETI
is
pushed to the stack and interrupts are enabled. For example, when pro-
cessing interrupt 7 (
IPEND[7:0] = 0x80
), another interrupt 7 request
causes software to again vector to the interrupt 7 service routine.
Self-nesting of interrupts applies only to core interrupts or inter-
rupts generated using the
RAISE
instruction; it is not allowed with
peripheral interrupts.
For the interrupt system to allow self-nesting, software must set bit
SNEN
(self-nesting enable) in
SYSCFG
. See
Figure 4-3 on page 4-6
. In self-nesting
mode, the system sets the LSB of the address in the return register
RETI
(
RETI[0]
) to indicate an incoming interrupt has the same priority as an
interrupt that is currently being serviced. The bit
RETI[0]
is automatically
set on entry into an interrupt service routine, and it is simply used as a sta-
tus bit to flag the processor that the current ISR is self-nesting.
Summary of Contents for ADSP-BF535 Blackfin
Page 80: ...Development Tools 1 26 ADSP BF535 Blackfin Processor Hardware Reference...
Page 312: ...Working With Memory 6 86 ADSP BF535 Blackfin Processor Hardware Reference...
Page 332: ...System Interfaces 7 20 ADSP BF535 Blackfin Processor Hardware Reference...
Page 360: ...Dynamic Power Management Controller 8 28 ADSP BF535 Blackfin Processor Hardware Reference...
Page 446: ...Beginning and Ending an SPI Transfer 10 40 ADSP BF535 Blackfin Processor Hardware Reference...
Page 522: ...Timing Examples 11 76 ADSP BF535 Blackfin Processor Hardware Reference...
Page 562: ...IrDA Support 12 40 ADSP BF535 Blackfin Processor Hardware Reference...
Page 608: ...PCI I O Issues 13 46 ADSP BF535 Blackfin Processor Hardware Reference...
Page 672: ...References 14 64 ADSP BF535 Blackfin Processor Hardware Reference...
Page 810: ...SDRAM Controller SDC 18 86 ADSP BF535 Blackfin Processor Hardware Reference...
Page 811: ...ADSP BF535 Blackfin Processor Hardware Reference 18 87 External Bus Interface Unit...
Page 812: ...SDRAM Controller SDC 18 88 ADSP BF535 Blackfin Processor Hardware Reference...
Page 860: ...DMA Bus Debug Registers 20 30 ADSP BF535 Blackfin Processor Hardware Reference...