10.3.9.2 EM23 Voltage Scaling
The EM23VSCALE bitfield in EMU_CTRL allows user to independently setup the voltage scaling value for EM23 energy mode. The
EM23VSCALE in EMU_CTRL should be programmed to a level which is less than or equal to VSCALE in EMU_STATUS. This means
that EM23 voltage scaling is always a voltage scaling down process. If EM23VSCALE level in EMU_CTRL is greater than VSCALE
level in EMU_STATUS, the VSCALE level will be implemented in EM23 instead of EM23VSCALE. Upon EM23 entry, the system will
scale down the voltage to a smaller level between VSCALE or EM23VSCALE.
Note:
The reset value of EM23VSCALE is Voltage Scale Level 2. Therefore, if user scales EM01 voltage to Voltage Scale Level 0 (re-
flected in VSCALE in EMU_STATUS) and enters EM23, this VSCALE voltage of Voltage Scale Level 0 is maintained in EM23 as well
since this is smaller level between VSCALE and EM23VSCALE.
10.3.9.2.1 EM23 Voltage Scaling Guidelines
Note that when using EM23VSCALE in EMU_CTRL to scale down EM23, the scaled down voltage in EM23 is maintained after waking
from EM23 to EM01. For example, if VSCALE was at Voltage Scale Level 2 prior to EM23 entry, and EM23VSCALE was set to Voltage
Scale Level 0, the system will scale down to Voltage Scale Level 0 on EM23 entry. When waking up to EM01, the system maintains its
voltage at Voltage Scale Level 0. Therefore, user must ensure the system clock frequency and Flash wait states are programmed to
correct values to support waking up to EM01 at the lower voltages prior to EM23 entry.
EM23VSCALEAUTOWSEN bitfield in EMU_CTRL enables hardware to automatically configure the system clock frequency and Flash
wait states to support low voltage operation when waking up to EM01 from EM23. Therefore, this obviates the need for user to setup
the clock frequency and Flash wait states prior to EM23 entry with EM23VSCALE.
10.3.9.3 EM4H Voltage Scaling
EM4HVSCALE bitfield in EMU_CTRL allows user to independently setup the voltage scaling levels for EM4H energy mode. The
EM4HVSCALE in EMU_CTRL should be programmed to a level which is smaller than or equal to VSCALE level in EMU_STATUS or
EM23VSCALE in EMU_CTRL. This means that EM4H voltage scaling is always a voltage scaling down process. If EM4HVSCALE level
in EMU_CTRL is greater than level of VSCALE in EMU_STATUS or level of EM23VSCALE in EMU_CTRL, the smaller of VSCALE,
EM23VSCALE or EM4HVSCALE levels will be implemented in EM4H.
Note:
The reset level of EM4HVSCALE is Voltage Scale Level 2. Therefore, if user scales EM01 voltage to Voltage Scale Level 0 (re-
flected in VSCALE in EMU_STATUS) and enters EM4H, this VSCALE voltage of Voltage Scale Level 0 is maintained in EM23 as well
since this is minimum of VSCALE and EM23VSCALE.
10.3.9.3.1 EM4H Voltage Scaling Guidelines
Note that when using EM4HVSCALE in EMU_CTRL to scale down voltage in EM4H, the scaled down voltage in EM4H is maintained
after waking from EM4H to EM01. For example prior to EM4H entry, if VSCALE was at Voltage Scale Level 2 and EM4HVSCALE was
set to Voltage Scale Level 0, the system will scale down to Voltage Scale Level 0 on EM4H entry. When waking up to EM01, the system
maintains its voltage at Voltage Scale Level 0.
10.3.9.4 Voltage Scaling Recommended Use
Refer to the data sheet for the maximum supported system frequencies for different Voltage Scaling Levels. Use of the lowest voltage
scaling level is recommended for maximum power savings. For any voltage scaling level, it is recommend to use the highest frequency
for performance benefits.
Voltage can then be scaled to higher voltage scale levels only when higher system clock frequency is required by the application for a
period of time after which user can dynamically scale the voltage back to lower voltage scale levels to continue saving power.
Reference Manual
EMU - Energy Management Unit
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