Low Power Modes
142
SPRUHE8E – October 2012 – Revised November 2019
Copyright © 2012–2019, Texas Instruments Incorporated
System Control and Interrupts
summarizes the low-power modes on the M3 subsystem.
(1)
The low-power mode clock gating scheme will suppress the debug accesses in sleep and deep sleep mode.
(2)
If the user exits deep-sleep mode, the user must not re-enter this mode within 5us otherwise the PLL timing may get affected.
(3)
Turning OSC off in deep-sleep mode is not supported.
Table 1-25. M3 Subsystem Low-Power Modes
Mode
Enter Using
Oscillator clock
PLL
(can be
turned off /
on
depending
on
SYSCLKCT
L register)
X1, X2
FCLK to M3
CPU
HCLK to M3
CPU
Exit
SLEEP
(1)
Sleep Now
WFE / WFI
instructions
on
on
on
on
off
Any event
for WFE /
Any interrupt
for WFI
Sleep on Exit
Set Sleep-on-exit bit
of
Cortex M3
SYSCTRL register
+WFE/WFI
on
on
on
on
off
Any event
for WFE /
Any interrupt
for WFI
DEEP
SLEEP
(1) (2)
Set SLEEPDEEP bit
of
Cortex M3
SYSCTRL register
+ Sleep now or
Sleep-on-exit
On but lower
frequency
(3)
(Refer to the
DSLPCLKCFG
register)
off
On
on
off
Any event
for WFE /
Any interrupt
for WFI
The SLEEPDEEP bit of the System Control (SYSCTRL) register selects which sleep mode is used. Refer
to the SYSCTRL register description in the
Cortex-M3 Peripherals
chapter for more details.
1.9.1.1.1 Entering Low-Power Mode
This section describes the mechanisms for entering low-power mode and the conditions for waking up
from low-power mode, both of which apply to sleep mode and deep-sleep mode.
The only distinguishing factor between selecting sleep or deep sleep as the system’s low-power mode is
the SLEEPDEEP bit of the M3 System Control (SYSCTRL) register. The value of this bit indicates the low-
power mode selection for the system.
SLEEPDEEP Value
Description
0
Use sleep mode as the low power mode
1
Use deep-sleep mode as the low power mode
All the mechanisms below can be used to enter either sleep or deep sleep mode.
1.9.1.1.1.1 WAIT For INTERRUPT
The wait for interrupt instruction, WFI, causes immediate entry to sleep mode unless the wake-up
condition is true (see
). When the processor executes a WFI instruction, it stops
executing instructions and enters sleep mode. See the
Cortex™-M3 Instruction Set Technical User's
Manual
for more information.