Power, Reset, and Clock Management
8.1.4.6.1 Periodic Idling of Cortex A8 MPU
To implement Cortex A8 MPU periodic ON/OFF in the use case, the control flow could be implemented
according to the following steps:
1. Cortex A8 MPU executes WFI instruction
2. Any peripheral interrupt in any of the next steps will trigger a wake interrupt to CortexM3 via MPU
Subsystem’s WKUP signal (INTR2 shown on the diagram). Cortex M3 powers down the
MPU(PD_MPU)
3. On receiving an interrupt Cortex M3 switches ON the MPU power domain by turning on PD_MPU
4. Cortex M3 goes into idle mode using WFI instruction
8.1.4.6.2 Sleep Sequencing
This section gives the system level guidelines for sleep sequencing. The guidelines can serve as an
example for implementing the sleep mode sequencing. The user can opt to implement a sequence with
certain steps interchanged between the MPU and Cortex M3 processor.
1. Application saves context of peripherals to memories supporting retention and DDR – this step is only
required for Deepsleep0.
2. MPU OCMC_RAM remains in retention
3. Unused power domains are turned OFF - program clock/power domains PWRSTCTRL, save contexts
etc
4. Software populates L3_OCMC_RAM for wakeup restoration viz Save EMIF settings, public restoration
pointers, etc.
5. Execute WFI from SRAM
6. Any peripheral interrupt will trigger a wake interrupt to CortexM3 via Cortex A8 MPU’s WKUP signal
(INTR2 shown on the diagram).
7. After MPU power domain is clock gated PRCM will provide an interrupt to CortexM3 (using INTR1
shown in the block diagram)
8. CortexM3 starts execution and performs low level power sequencing to turn off certain power domain,
and eventually executes WFI.
9. Hardware oscillator control circuit disables the oscillator once CortexM3 goes into WFI
8.1.4.6.3 Wakeup Sequencing
This section gives the guidelines for Wakeup sequencing.
1. One of the wakeup event triggers (which was configured during the sleep sequencing) will initiate a
wakeup sequence
2. The wake up event will switch on the oscillator (if it was configured to go OFF during sleep)
3. The wake up event will also trigger interrupt to Cortex M3
4. On the wakeup event due to interrupt Cortex M3 execute the following
•
Restore the voltages to normal Operating voltage
•
Enable PLL locking
•
Cortex M3 will switch ON the power domains and/or enable clocks for PD_PER
•
Cortex M3 will switch ON the power domains and/or enable clocks for PD_MPU
•
Executes WFI
5. Cortex A8 MPU starts executing from ROM reset vector
6. Restore the application context(only for Deep sleep 0)
8.1.5 PRCM Module Overview
The PRCM is structured using the architectural concepts presented in the 5000x Power Management
Framework. This framework provides:
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SPRUH73H – October 2011 – Revised April 2013
Power, Reset, and Clock Management (PRCM)
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