NXP Semiconductors MPC5644A, Reference Manual, Page: 374 / 1735

Interrupt Controller (INTC)
MPC5644A Microcontroller Reference Manual, Rev. 6
374 Freescale Semiconductor
wrteei 1 # enable processor recognition of interrupts
code to save rest of context required by e500 EABI
bl ISR x # branch to ISR for interrupt with vector x
epilog:
code to restore most of context required by e500 EABI
# Popping the LIFO after the restoration of most of the context and the disabling of processor
# recognition of interrupts eases the calculation of the maximum stack depth at the cost of
# postponing the servicing of the next interrupt request.
mbar # ensure store to clear flag bit has completed
lis r3,INTC_EOIR@ha # form adjusted upper half of INTC_EOIR address
li r4,0x0 # form 0 to write to INTC_EOIR
wrteei 0 # disable processor recognition of interrupts
stw r4,INTC_EOIR@l(r3) # store to INTC_EOIR, informing INTC to lower priority
code to restore SRR0 and SRR1, restore working registers, and delete stack frame
rfi
ISR x :
code to service the interrupt event
code to clear flag bit which drives interrupt request to INTC
blr # branch to epilog
15.6.3 ISR, RTOS, and task hierarchy
The RTOS and all of the tasks under its control typically execute with PRI in INTC current priority register
(INTC_CPR) having a value of 0. The RTOS execute the tasks according to whatever priority scheme that
it has, but that priority scheme is independent and has a lower priority of execution than the priority scheme
of the INTC. In other words, the ISRs execute above INTC_CPR priority 0 and outside the control of the
RTOS, the RTOS executes at INTC_CPR priority 0, and while the tasks execute at different priorities
under the control of the RTOS, they also execute at INTC_CPR priority 0.
If a task shares a resource with an ISR and the PCP is being used to manage that shared resource, then the
task’s priority can be elevated in the INTC_CPR while the shared resource is being accessed.
An ISR whose PRI n in INTC priority select registers (INTC_PSR0–INTC_PSR485) has a value of 0 does
not cause an interrupt request to the processor, even if its peripheral or software configurable interrupt
request is asserted. For a peripheral interrupt request, not setting its enable bit or disabling the mask bit
causes it to remain negated, which consequently also does not cause an interrupt request to the processor.
Since the ISRs are outside the control of the RTOS, this ISR does not run unless called by another ISR or
the interrupt exception handler, perhaps after executing another ISR.