Functional Description
ARM DDI 0500D
Copyright © 2013-2014 ARM. All rights reserved.
2-25
ID021414
Non-Confidential
•
All system registers are saved.
•
All debug related state is saved.
5.
Execute an
ISB
instruction to ensure that all of the register changes from the previous steps
have been committed.
6.
Execute a
DSB
instruction to ensure that all cache, TLB and branch predictor maintenance
operations issued by any core in the cluster before the SMPEN bit was cleared have
completed. In addition, this ensures that all state saving has completed.
7.
Execute a
WFI
instruction and wait until the
STANDBYWFI
output is asserted, to indicate
that the core is in idle and low power state.
8.
Repeat the previous steps for all cores, and wait for all
STANDBYWFI
outputs to be
asserted.
9.
If the ACP interface is configured, ensure that any master connected to the interface does
not send new transactions, then assert
AINACTS
.
10.
If ACE is implemented, the SoC asserts the input pin
ACINACTM
to idle the AXI master
interface after all snoop transactions have been sent on the interface. If CHI is
implemented, the SoC asserts the input pin
SINACT
.
When the L2 has completed the outstanding transactions for the AXI master and slave
interfaces,
STANDBYWFIL2
is asserted to indicate that L2 memory system is idle. All
Cortex-A53 processor implementations contain an L2 memory system, including
implementations without an L2 cache.
11.
When all cores
STANDBYWFI
and
STANDBYWFIL2
are asserted, the cluster is ready
to enter Dormant mode.
12.
Activate the L2 cache RAM input clamps.
13.
Remove power from the PDCPU and PDCORTEXA53 power domains.
To exit Dormant mode, apply the following sequence:
1.
Apply a normal cold reset sequence. You must apply resets to the cores and the L2
memory system logic until power is restored. During this reset sequence,
L2RSTDISABLE
must be held HIGH to disable the L2 cache hardware reset
mechanism.
2.
When power has been restored, release the L2 cache RAM input clamps.
3.
Continue a normal cold reset sequence with
L2RSTDISABLE
held HIGH.
4.
The architectural state must be restored, if required.
Retention state
Contact ARM for information about retention state.
2.4.3
Event communication using WFE or SEV
An external agent can use the
EVENTI
pin to participate in a WFE or SEV event
communication with the Cortex-A53 processor. When this pin is asserted, it sends an event
message to all the cores in the device. This is similar to executing a
SEV
instruction on one core
in the cluster. This enables the external agent to signal to the cores that it has released a
semaphore and that the cores can leave the WFE low-power state. The
EVENTI
input pin must
remain HIGH for at least one
CLKIN
clock cycle to be visible by the cores.