A4.9
Power up and down sequences
The following approach allows taking the Cortex-A76 cores in the cluster in and out of coherence.
Core powerdown
To take a core out of coherence ready for core powerdown, the following power down steps must be
performed:
1. Save all architectural states.
2. Configure the GIC distributor to disable or reroute interrupts away from this core.
3. Set the CPUPWRCTLR.CORE_PWRDN_EN bit to 1 to indicate to the power controller that a
powerdown is requested.
4. Execute an
ISB
instruction.
5. Execute a
WFI
instruction.
All L1 and L2 cache disabling, L1 and L2 cache flushing, and communication with the L3 memory
system is performed in hardware after the
WFI
is executed, under the direction of the power controller.
Note
Executing any
WFI
instruction when the CPUPWRCTLR.CORE_PWRDN_EN bit is set automatically
masks out all interrupts and wake-up events in the core. If executed when the
CPUPWRCTLR.CORE_PWRDN_EN bit is set the WFI never wakes up and the core needs to be reset to
restart.
For information about cluster powerdown, see the
Arm
®
DynamIQ
™
Shared Unit Technical Reference
Manual
.
Core powerup
To bring a core into coherence after reset, no software steps are required.
Related references
B2.31 CPUPWRCTLR_EL1, Power Control Register, EL1
on page B2-188
A4 Power management
A4.9 Power up and down sequences
100798_0300_00_en
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Summary of Contents for Cortex-A76 Core
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