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Functional Description
212
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
System Control
NOTE:
If the Cortex-M4F Debug Access Port (DAP) has been enabled, and the device wakes from
a low-power sleep or deep-sleep mode, the core may start executing code before all clocks
to peripherals have been restored to their run mode configuration. The DAP is usually
enabled by software tools accessing the JTAG or SWD interface when debugging or flash
programming. If this condition occurs, a Hard Fault is triggered when software accesses a
peripheral with an invalid clock.
A software delay loop can be used at the beginning of the interrupt routine that is used to
wake up a system from a WFI instruction. This stalls the execution of any code that
accesses a peripheral register that might cause a fault. This loop can be removed for
production software, because the DAP is most likely not enabled during normal execution.
Because the DAP is disabled by default (after a POR), the user can also reset the device.
The DAP is not enabled unless it is enabled through the JTAG or SWD interface.
4.1.6.3
Deep-Sleep Mode
In deep-sleep mode, the clock frequency of the active peripherals may change (depending on the deep-
sleep mode clock configuration) in addition to the processor clock being stopped. An interrupt returns the
microcontroller to run mode from one of the sleep modes; the sleep modes are entered on request from
the code. Deep-sleep mode is entered by first setting the SLEEPDEEP bit in the System Control
(
) register and then executing a WFI instruction. Any properly configured interrupt event in the
system returns the processor to run mode. See
for more details.
NOTE:
If the DAP is enabled in run mode and the device tries to transition into deep-sleep mode,
the device is prevented from entering deep-sleep mode.
The Cortex-M4F processor core and the memory subsystem are not clocked in deep-sleep mode.
Peripherals are clocked if enabled in the peripheral-specific DCGC registers when automatic clock gating
is enabled or in the peripheral-specific RCGC registers when automatic clock gating is disabled.
The system clock source is specified in the DSCLKCFG register. When the DSCLKCFG register is used,
the internal oscillator source is powered up, if necessary, and other clocks are powered down. If the PLL
is running at the time of the WFI instruction, hardware shuts down the PLL for power savings. For
additional power savings, the PIOSC can be disabled through the PIOSCPD bit in the DSCLKCFG
register. When the deep-sleep exit event occurs, hardware returns the system clock to the source and
frequency it had at the start of deep-sleep mode before enabling the clocks that had been stopped during
deep-sleep mode. If the PIOSC is used as the PLL reference clock source, it may continue to provide the
clock during deep-sleep mode (see
).
NOTE:
If the MOSC is chosen as the deep-sleep clock source in the DSCLKCFG register, the
MOSC must also be configured as the run and sleep clock source in the RSCLKCFG register
before entering deep-sleep mode. If the PIOSC, LFIOSC, or Hibernation RTC module
oscillator (HIBLFIOSC or 32-kHz crystal) is configured as the run and sleep clock source in
the RSCLKFCFG register, and the MOSC is configured as the deep-sleep clock source in
the DSCLKCFG register, then two outcomes are possible:
•
If the PIOSC is still powered in deep sleep (using the PIOSCPD bit in the DSCLKCFG
register), the PIOSC is used as the clock source when entering deep sleep, and the
device enters and exits deep-sleep mode normally. The MOSC is not used as the clock
source in deep-sleep mode.
•
If the PIOSC has been configured to be powered down in deep-sleep mode, the device
can enter deep-sleep mode but cannot exit properly. This situation can be avoided by
programming the MOSC as the run and sleep clock source in the RSCLKCFG register
before entering deep-sleep mode.