Arm
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CoreLink™ GIC-600AE Generic Interrupt Controller
Technical Reference Manual
Document ID: 101206_0003_04_en
Issue: 04
Operation
4.16.5 Isolating a chip from the system
You can isolate a chip from the system.
About this task
To isolate a chip from the system, use the following procedure:
Procedure
1. Ensure that all cores on the chip are asleep by setting GICR_WAKER.ProcessorSleep.
2. Ensure all ITS blocks on the chip are disabled and the buses are quiesced by using the
qreqn_its<n> Q-Channel interfaces.
Before isolating the chip, the ITSs must be powered off because the Routing table is invalid
when the GIC P-Channel is in the OFF state.
3. Ensure that LPIs from other chips are not routed to this chip.
4. Attempt to enter the CONFIG state (pstate signal = 0x9).
If the GIC is idle and all credits are returned, it accepts the request to go into CONFIG state,
otherwise it denies the request and remains in RUN state.
All SPIs must return to their own chip before a request is accepted. This means
that SPIs that are enabled and pending, but targeting a core on a remote chip
where the relevant CPU group is disabled, prevent transition into the CONFIG
state.
When in the CONFIG state, any cross-chip messages that change the internal state are held in
the cross-chip interface, and all messages assert the pactive signal. If the pactive signal asserts
while attempting to enter a lower power state, you must return to RUN (pstate signal == 0x0).
5. When in CONFIG state, any required state can be saved.
Writing to GICD_CHIPRn or GICD_DCHIPR for any purpose other than to restore saved values
after a hardware reset is unpredictable.
6. Power down the Redistributors using the GICR_PWRR registers.
7. Flush the LPI cache using GICR_WAKER.Sleep.
We recommend that if wake-on-interrupt is required, LPIs from other chips do not target this
chip while the chip is being powered down (step 3 on page 92). Also, LPIs from other chips
must be routed back while the chip is in the OFF state.
If LPIs arrive after sleep is set in the CONFIG state, then the LPIs are dropped.
8. Attempt to enter the OFF state.
If the pactive signal is HIGH, return to the CONFIG state.
9. Use the Q-Channel to put the GIC into a safe mode to reset.
If the SPI Collator is in a different domain to the Distributor and only one of the domains is
being reset, then the power Q-Channel must have also accepted before the reset can occur.
This might require masking interrupts outside of the GIC to ensure that all interrupt lines have
reached their idle state.
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