Power Management
15-48
J
RTC (on–chip Real–time–clock) registers and logic.
Since only selective peripheral registers are reset by a warm-reset via
MPU_RST assertion, it is recommended that the safest approach in using the
MPU_RST signal for warm-reset is to always perform a complete system
re-initialization at re-boot.
The OMAP5910 device implements a single low power pin (LOW_PWR) that
indicates to external logic that the device is in low power mode or deep sleep
mode. The LOW_PWR signal is multiplexed on the same pin as the MPUIO5
signal, so to utilize the low power function, user software needs to configure
the pin appropriately as LOW_PWR. A warm reset condition (MPU_RST
active) has the following effects on the LOW_PWR output pin:
Given a warm reset condition when OMAP5910 is awake:
-
Multiplexing logic responsible for driving LOW_PWR onto the correct pin
is not reset.
-
The LOW_PWR pin remains low
Given a warm reset condition when OMAP5910 is in low power or deep sleep
mode:
-
Multiplexing logic responsible for driving LOW_PWR onto the correct pin
is not reset.
-
The LOW_PWR pin transitions from high to low.
OMAP5910 implements a deep sleep mode wherein the 12 MHz oscillator is
powered down. A MPU_RESET event will alert the ULPD module, which will
turn on the 12 MHz oscillator. When this oscillator’s clock is stable, the re-boot
of the ARM9 can begin. The time required for oscillator stability is defined by
the value programmed in the analog delay counter.
15.3.10
Power Control for External Devices
The idle and wake-up control module implements a power control for external
devices through the FLASH.RP output pin. The FLASH.RP signal is asserted
low for eight input clock cycles (Trl) when a global reset occurs.
Before an idle/wake-up sequence entry, the external power control can be
enabled/disabled and the time can be programmed depending on the system
application. When a global reset is asserted, the timing of the FLASH.RP
signal is fixed as shown in Figure 15–15. The eight cycle count starts from
when the MPU_RST pin is detected high (OMAPNRST). This means that there