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PMU Sequencing

BCM4354 Data Sheet

BROADCOM CONFIDENTIAL

Broadcom®

October 15, 2014 • 4354-DS109-R

Page 25

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 non-zero 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.

BCM4354 データシート(PDF) 26 Page - Cypress Semiconductor