Exiting LPM3 or LPM4 Mode – DMA Trigger Based Wakeup (Not Applicable for MSP432P401R and MSP432P401M Devices)
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SLAU356I – March 2015 – Revised June 2019
Copyright © 2015–2019, Texas Instruments Incorporated
Power Control Manager (PCM)
8.19 Exiting LPM3 or LPM4 Mode – DMA Trigger Based Wakeup (Not Applicable for
MSP432P401R and MSP432P401M Devices)
In all devices except MSP432P401R and MSP432P401M, wakeup from LPM3 or LPM4 modes upon DMA
trigger from peripherals as well as external DMA trigger pin (DMAE0) is possible. It is necessary to
configure the channel specific trigger source configuration registers in the DMA module for wake up from
LPM3 or LPM4 modes in addition to configuring the peripherals or device pin for DMA trigger. For the
DMA trigger from the device pin, it is required to configure the pin to the correct secondary function
through PxSELy registers and also the direction to be input through PxDIR register.
It is not possible to exit from LPM3.5 or LPM4.5 modes upon DMA trigger from peripherals or device pin.
In active and LPM0 modes the functionality of DMA trigger from peripherals as well as device pin is
preserved and leads to DMA data transfer if the DMA is configured properly.
Device enters LPM0 mode upon wake up due to DMA triggers and DMA carries out the data transfer.
CPU is inactive and remains in the clock gated state. Device remains in LPM0 itself after DMA transfers
are completed. Device can go into active mode either upon DMA DONE interrupt condition or upon other
peripheral/pin interrupts. If re-entry into LPM3 or LPM4 is desired, then sleep-on-exit may be programmed
in the Arm core and LPM3 or LPM4 mode will be restored after ISR execution is completed.
8.20 Entering LPM3.5 and LPM4.5 Modes
LPM3.5 and LPM4.5 entry and exit is different from the other low-power modes. LPM3.5 and LPM4.5
modes, when used properly, give the lowest power consumption available on a device. To achieve this,
entry to LPM3.5 and LPM4.5 disables the majority of the circuitry on the device by removing supply power.
Because the supply voltage is removed from the circuitry, most register contents and SRAM contents are
lost. For LPM3.5, the only modules available are the RTC and WDT, and bank 0 of SRAM is in retention
mode. These modules are optionally active and are selectable by the user. For LPM4.5, no module
functionality is available. In LPM4.5, the complete core logic supply is turned off, and power is completely
removed from all the circuitry. During LPM4.5 operation, only the minimum circuitry is powered that is
required to wake-up the device.
The basic steps for entry into LPM3.5 and LPM4.5 modes follow. Details about the operation of RTC,
WDT, and Digital I/O during LPMx.5 modes can be found in the respective module chapters.
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Set LOCKLPM5 = 0 and LOCKBKUP = 0, which may have been set from a previous LPMx.5 entry.
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Configure I/Os appropriately. See the Digital I/O chapter for complete details on configuring I/O for
LPMx.5 modes.
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Set all ports to general-purpose I/O. Configure each port to ensure no floating inputs based on the
application requirements.
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If wake-up input from an I/O is desired, configure the wake-up I/O ports appropriately.
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For LPM3.5, if RTC operation is desired, enable the RTC. In addition, configure any RTC interrupts, if
desired for a LPM3.5 wake-up event. See the RTC chapter for complete details.
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Enter LPM3.5 or LPM4.5 by writing LPMR = Ah or Ch, respectively and setting SLEEPDEEP = 1 in
SCR.
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The device waits for a WFI, WFE, or sleep-on-exit event. Upon entering LPMx.5 mode, the I/O pin
conditions remain locked at their current state. Also the LOCKLPM5 and LOCKBKUP bits are
automatically set on entry into LPM3.5 mode. Only the LOCKLPM5 bit is set on entry into LPM4.5
mode.
NOTE:
Before LPM3.5 entry, the application must configure the watchdog timer in the
interval timer mode and not in the watchdog mode. Failure to do so might trigger a
soft or hard reset condition during the low-power mode transitions. This could result
in the system being in an indeterministic state.
NOTE:
Clocks brought out on device pins also cause clock requests to the respective
clocks in the device. The application should therefore treat these similar to other
peripherals when entering LPM3.5 or LPM4.5 mode.