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MPC563XM Reference Manual, Rev. 1
438
Freescale Semiconductor
Preliminary—Subject to Change Without Notice
to a SET
x
bit on the second processor. The second processor, after accessing the block of data, clears the
corresponding CLR
x
bit and then writes ‘1’ to a SET
x
bit on the first processor, informing it that it now
can access the block of data.
14.7.9
Lowering Priority Within an ISR
In SoC implementations without the software setable interrupt requests in
Software Set/Clear Interrupt Registers (INTC_SSCIR0_3 - INTC_SSCIR4_7)
besides scheduling a task through an RTOS to not have priority inversion with an ISR whose work spans
multiple priorities as described in
Section 14.7.8.1, “Scheduling a Lower Priority Portion of an ISR
lower the current priority. However, the INTC has a LIFO whose depth is determined by the number of
priorities.
NOTE
Lowering the PRI value in either
Section 14.5.4, “INTC Current Priority
Register for Processor 0 (INTC_CPR_PRC0)
Current Priority Register for Processor 1 (INTC_CPR_PRC1)
” within an
ISR to below the ISR’s corresponding PRI value in
Priority Select Registers (INTC_PSR0_3 - INTC_PSR508_511)
more preemptions than the depth of the LIFO can support.
Therefore, the INTC does not support lowering the current priority within an ISR as a way to avoid priority
inversion.
14.7.10 Negating an Interrupt Request Outside of its ISR
14.7.10.1 Negating an Interrupt Request as a Side Effect of an ISR
Some peripherals have flag bits which can be cleared as a side effect of servicing a peripheral interrupt
request. For example, reading a specific register can clear the flag bits, and consequently their
corresponding interrupt requests too. This clearing as a side effect of servicing a peripheral interrupt
request can cause the negation of other peripheral interrupt requests besides the peripheral interrupt request
whose ISR presently is executing. This negating of a peripheral interrupt request outside of its ISR can be
a desired effect.
14.7.10.2 Negating Multiple Interrupt Requests in One ISR
An ISR can clear other flag bits besides its own flag bit. One reason that an ISR clears multiple flag bits
is because it serviced those other flag bits, and therefore the ISRs for these other flag bits do not need to
be executed.
14.7.10.3 Proper Setting of Interrupt Request Priority
Whether an interrupt request negates outside of its own ISR due to the side effect of an ISR execution or
the intentional clearing a flag bit, the priorities of the peripheral or software setable interrupt requests for
these other flag bits must be selected properly. Their PRI
x
values in
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