During Compute Operation, the AIPS peripheral space is disabled and attempted accesses
generate bus errors. The private peripheral bus (PPB) remains accessible during Compute
Operation, including the MCM, System Control Space (SCS) (for NVIC and FPU), and
SysTick. Although access to the GPIO registers is supported, the GPIO port data input
registers do not return valid data since clocks are disabled to the Port Control and
Interrupt modules. By writing to the GPIO port data output registers, it is possible to
control those GPIO ports that are configured as output pins.
Compute Operation is controlled by the CPO register in the MCM, which is only
accessible to the CPU. Setting or clearing the CPOREQ bit in the MCM initiates entry or
exit into Compute Operation. Compute Operation can also be configured to exit
automatically on detection of an interrupt, which is required in order to service most
interrupts. Only the core system interrupts (exceptions, including NMI and SysTick) and
any edge sensitive interrupts can be serviced without exiting Compute Operation.
When entering Compute Operation, the CPOACK status bit indicates when entry has
completed. When exiting Compute Operation in Run mode, the CPOACK status bit
negates immediately. When exiting Compute Operation in VLP Run mode, the exit is
delayed to allow the PMC to handle the change in power consumption. This delay means
the CPOACK bit is polled to determine when the AIPS peripheral space can be accessed
without generating a bus error.
The DMA wakeup is also supported during Compute Operation and causes the CPOACK
status bit to clear and the AIPS peripheral space to be accessible for the duration of the
DMA wakeup. At the completion of the DMA wakeup, the device transitions back into
Compute Operation.
7.2.4 Peripheral Doze
Several peripherals support a Peripheral Doze mode, where a register bit can be used to
disable the peripheral for the duration of a low-power mode. The flash memory can also
be placed in a low-power state during Peripheral Doze via a register bit in the SIM.
Peripheral Doze is defined to include all of the modes of operation listed below.
• The CPU is in Wait mode.
• The CPU is in Stop mode, including the entry sequence and for the duration of a
DMA wakeup.
• The CPU is in Compute Operation, including the entry sequence and for the duration
of a DMA wakeup.
Clocking modes
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Freescale Semiconductor, Inc.