BCM88335 Data Sheet
PMU Sequencing
PMU Sequencing
The PMU sequencer is responsible for minimizing system power consumption. It enables and disables various
system resources based on a computation of the required resources and a table that describes the relationship
between resources and the time needed to enable and disable them.
Resource requests may come from several sources: clock requests from cores, the minimum resources defined
in the ResourceMin register, and the resources requested by any active resource request timers. The PMU
sequencer maps clock requests into a set of resources required to produce the requested clocks.
Each resource is in one of four states (enabled, disabled, transition_on, and transition_off) and has a timer that
contains 0 when the resource is enabled or disabled and a nonzero value in the transition states. The timer is
loaded with the time_on or time_off value of the resource when the PMU determines that the resource must be
enabled or disabled. That timer decrements on each 32.768 kHz PMU clock. When it reaches 0, the state
changes from transition_off to disabled or transition_on to enabled. If the time_on value is 0, the resource can
go immediately from disabled to enabled. Similarly, a time_off value of 0 indicates that the resource can go
immediately from enabled to disabled. The terms enable sequence and disable sequence refer to either the
immediate transition or the timer load-decrement sequence.
During each clock cycle, the PMU sequencer performs the following actions:
•
•
Computes the required resource set based on requests and the resource dependency table.
Decrements all timers whose values are non zero. If a timer reaches 0, the PMU clears the
ResourcePending bit for the resource and inverts the ResourceState bit.
•
•
•
Compares the request with the current resource status and determines which resources must be enabled
or disabled.
Initiates a disable sequence for each resource that is enabled, no longer being requested, and has no
powered up dependents.
Initiates an enable sequence for each resource that is disabled, is being requested, and has all of its
dependencies enabled.
Broadcom®
September 23, 2015 • 88335-DS100-R
Page 24
BROADCOM CONFIDENTIAL
CYPRESS [ CYPRESS ]
