Power Management Modes; Strongarm Power Management Modes; Power Management On The Bitsy Plus - Applied Data Systems Bitsy Plus User Manual

Bitsy Plus User's Manual
5.2

Power Management Modes

Handheld and portable systems available today never really turn "off." They make use of power
management algorithms that cycle the electronics into "standby" and "sleep" modes, but never
fully remove power from the full system.
This section describes the various power management modes of the StrongARM processor and
how the Bitsy Plus makes use of them.
5.2.1

StrongARM Power Management Modes

The StrongARM SA-1110 processor supports three operational modes: RUN, IDLE, and SLEEP.
RUN mode offers the greatest performance at the highest cost in power consumption. IDLE mode
defines operation with reduced power consumption from RUN mode while offering a shorter
transition time to RUN than from SLEEP. In IDLE mode, the StrongARM continues to run, while
unused peripherals are disabled. SLEEP mode offers the greatest reduction of operating current.
The processor core is powered off and only a few peripherals (RTC, I/Os and interrupt control)
remain active.
5.2.2

Power Management on the Bitsy Plus

The Bitsy Plus can actively be configured to be in StrongARM RUN or SLEEP modes. IDLE
mode is controlled by the operating system and is typically transparent to the application.
In RUN and IDLE modes, the power supplies are in their standard, full-power state and
applications run normally on the system. Specific subsystems (as described in section 5.3.2) may
be selectively disabled to conserve power during these states.
In SLEEP mode, sometimes called "Suspend" mode, the processor puts the SDRAM in a low-
power, self-refresh mode, the processor core shuts off, most peripheral sub-systems are shut down
and the power supplies drop into low-power states or turn off entirely (see the diagram in section
5.3.2 for details). In this state, the Bitsy consumes very little power, most of which is dedicated to
the maintenance of the RAM (see section 6.2.5 for specifications). The system can be "awakened"
and returned to the RUN state by initiating a system wakeup using one of the methods described in
section 5.3.3.
If Main Power (DC_IN or VBATT_POS) drops below the power supply trip point (section 6.2.2),
the Bitsy Plus generates and interrupt that the operating system can use to put the system into
Sleep mode. The transition time from RUN mode to SLEEP mode is a function of the operating
system. System SLEEP can also be initiated programmatically.
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