Texas Instruments OMAP36 Series, Техническое справочное руководство

Страница: 353 / 3738

W
a
k
e
-u
p
tr
a
n
s
it
io
n
RETENTION
INACTIVE
OFF
ACTIVE
S
le
e
p
tr
a
n
s
it
io
n
Switch to retention
voltage
Switch to normal
operating voltage and
activate clocks
Cut
clocks
Switch to normal
operating voltage and
activate clocks
Switch voltage
to 0 V
Activate
clocks
D
e
v
ic
e
p
o
w
e
r
c
o
n
s
u
m
p
ti
o
n
prcm-071
Transient state
Public Version
www.ti.com
PRCM Functional Description
3.5.4 PRCM Idle and Wake-Up Management
3.5.4.1 Overview
When a group of modules belonging to a clock domain in a power domain does not require a clock
(interface or functional), the PRCM module can be programmed to automatically cut the clock to these
modules, thereby reducing their power consumption. The PRCM module can then switch the power
domain to low-power retention or off mode to ensure minimum power consumption. When all clocks in a
domain are cut, the domain is idle.
Similarly, when a module belonging to a power domain in low-power idle mode is required to switch to
active mode, the PRCM module switches on the power to the entire power domain and activates the
necessary clock signals to the module. This is a wake-up transition. Generally, a wake-up event triggers
the wake-up transition.
A sleep/wake-up dependency can be defined between power domains. A sleep dependency ensures that
a power domain does not make a sleep transition unless all the dependent power domains are in idle
mode and do not require the power domain. Similarly, a wake-up dependency ensures that a power
domain wakes up when any of its dependent power domains wakes up.
The PRCM module automatically handles the sequence clock-gating conditions and power switching for
each power domain, based on the configured dependencies between the domains and the clock-control
bits of the modules.
Figure 3-75 shows the sleep/wake-up transition of the power domains. The INACTIVE state is a transient
power state of a power domain, while moving from ACTIVE to RETENTION or OFF power state. In
INACTIVE state, all the domain clocks are gated. A power domain cannot switch from OFF to
RETENTION or RETENTION to OFF power state without passing to the ACTIVE power state.
A low-power state (INACTIVE, RETENTION, or OFF) means less power consumption. However, wake-up
latency increases as the power domain switches to INACTIVE, RETENTION, or OFF power state.
Figure 3-75. Power Domain Sleep/Wake-Up Transition
Functionally, the PRCM module is composed of a single global control block and a power-control block for
each power domain. The domain power-control block handles power switching, wake-up events, and
clock-gating control for the domain. The domain power controllers communicate with each other for power
sequencing, sleep dependencies, and wake-up dependencies. All these blocks interact with the global
control block that handles reset management, clock generation and distribution, and all PRCM registers.
353 SWPU177N – December 2009 – Revised November 2010 Power, Reset, and Clock Management
Copyright © 2009–2010, Texas Instruments Incorporated