ADSP-2126x SHARC Processor Hardware Reference
3-59
Program Sequencer
Programs should change the interrupt nesting enable (
NESTM
) bit only
while outside of an interrupt service routine or during the reset service
routine.
If nesting is enabled and a higher priority interrupt occurs immediately
after a lower priority interrupt, the service routine of the higher priority
interrupt is delayed by one cycle. This delay allows the first instruction of
the lower priority interrupt routine to be executed, before it is
interrupted.
When servicing nested interrupts, the DSP uses the interrupt mask
pointer (
IMASKP
) to create a temporary interrupt mask for each level of
interrupt nesting; the
IMASK
value is not effected. The DSP changes
IMASKP
each time a higher priority interrupt interrupts a lower priority ser-
vice routine.
The bits in
IMASKP
correspond to the interrupts in order of priority. When
an interrupt occurs, the DSP sets its bit in
IMASKP
. If nesting is enabled,
the DSP uses
IMASKP
to generate a new temporary interrupt mask, mask-
ing all interrupts of equal or lower priority to the highest priority bit set in
IMASKP
and keeping higher priority interrupts the same as in
IMASK
. When
a return from an interrupt service routine (
RTI
) is executed, the DSP clears
the highest priority bit set in
IMASKP
and generates a new temporary inter-
rupt mask.
The DSP masks all interrupts of equal or lower priority to the highest pri-
ority bit set in
IMASKP
. The bit set in
IMASKP
that has the highest priority
always corresponds to the priority of the interrupt being serviced.
The
MSKP
bits in the
LIRPTL
register, and the entire
IMASKP
register
are for interrupt controller use only. Modifying these bits interferes
with the proper operation of the interrupt controller. Furthermore,
explicit bit manipulation of
any
bit in the
LIRPTL
register while the
IRPTEN
bit (bit 12 in the
MODE1
register) is set causes an interrupt to
be serviced twice.
Summary of Contents for ADSP-21261 SHARC
Page 30: ...Contents xxx ADSP 2126x SHARC Processor Hardware Reference ...
Page 40: ...Register Diagram Conventions xl ADSP 2126x SHARC Processor Hardware Reference ...
Page 58: ...Differences From Previous SHARCs 1 18 ADSP 2126x SHARC Processor Hardware Reference ...
Page 112: ...Secondary Processing Element PEy 2 54 ADSP 2126x SHARC Processor Hardware Reference ...
Page 178: ...Summary 3 66 ADSP 2126x SHARC Processor Hardware Reference ...
Page 204: ...DAG Instruction Summary 4 26 ADSP 2126x SHARC Processor Hardware Reference ...
Page 322: ...Setting Up DMA 7 32 ADSP 2126x SHARC Processor Hardware Reference ...
Page 436: ...SPORT Programming Examples 9 86 ADSP 2126x SHARC Processor Hardware Reference ...
Page 521: ...ADSP 2126x SHARC Processor Hardware Reference 11 31 Input Data Port rts IDP_ISR end ...
Page 522: ...Input Data Port Programming Example 11 32 ADSP 2126x SHARC Processor Hardware Reference ...
Page 590: ...Timer Programming Examples 14 20 ADSP 2126x SHARC Processor Hardware Reference ...
Page 796: ...I O Processor Registers A 174 ADSP 2126x SHARC Processor Hardware Reference ...
Page 800: ...B 4 ADSP 2126x SHARC Processor Core Manual ...
Page 846: ...Index I 36 ADSP 2126x SHARC Processor Hardware Reference ...