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RTC-Only Mode
9.7
RTC-Only Mode
In real-time clock (RTC)-only mode, the RTC is powered on and the rest of the device is completely
powered off (all supplies except the RTC supply are removed). In this mode, the RTC is fully functional
and keeps track of date, hours, minutes, and seconds. In this mode, the overall power consumption would
be significantly lower, as voltage from the rest of the core and I/O logic can be completely removed,
eliminating most of the active and static power of the device, except for what is consumed by the RTC
module, running at 32 kHz.
NOTE:
To put the device in RTC-only mode, there is no software control sequence. You can put
the device in the RTC-only mode by removing the power supply from all core and I/O logic,
except for the RTC core logic supply (RTC_CVDD). During wake up, all power sequencing
requirements described in the device-specific data manual must be followed.
Some limitations apply in the RTC-only mode. First, the RTC_ALARM pin is not available as an option for
use as a control to signal an external power supply to reapply power to the rest of the device. This is
because the RTC_ALARM pin is powered by the I/O supply that is powered down in RTC-only mode.
Second, in RTC-only mode, only the RTC register contents are preserved, all other internal memory and
register contents are lost. Mobile DDR and DDR2 contents can be preserved through the use of
self-refresh (see
). However, software must be in place to restore the context of the device,
for example, reinitialize internal registers, setup cache memory configurations, interrupt vectors, etc.
9.8
Dynamic Voltage and Frequency Scaling (DVFS)
Dynamic voltage and frequency scaling (DVFS) consists of minimizing the idle time of the system. The
DVFS technique uses dynamic selection of the optimal frequency and voltage to allow a task to be
performed in the required amount of time. This reduces the total power consumption of the device while
still meeting task requirements. DVFS requires control over the clock frequency and the operating voltage
of the device elements. By intelligently switching these elements to their optimal operating points, it is
possible to minimize the power consumption of the device for a given task.
For reasons related to the device (clock architecture, process, etc.), DVFS is used only for a few discrete
steps, not over a continuum of voltage and frequency values. Each step, or operating performance point
(OPP), is composed of a voltage and frequency pair. For an OPP, the frequency corresponds to the
maximum frequency allowed at a voltage, or reciprocally; the voltage corresponds to the minimum voltage
allowed for a frequency. See your device data manual for a list of the OPPs supported by the device.
When applying DVFS, a processor or system always runs at the lowest OPP that meets the performance
requirement at a given time. You determine the optimal OPP for a given task and then switch to that OPP
to save power.
137
SPRUGX5A
–
May 2011
Power Management
Copyright
©
2011, Texas Instruments Incorporated
Содержание AM1802
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