Chapter 03 Power, Reset, and Clock Management.pdf

Normalized power
1.0
0.5
0
Without DPS
Leakage
1 2 3 4 5
Execution time
Energy consumed = 1.3 J
Public Version
Introduction to Power Managements www.ti.com
With SmartReflex, the frequency steps are identified and the voltage is adapted according to the silicon
performance of the device. In this case, instead of a voltage step for each frequency step, there is a
corresponding range of voltages. The range depends on the fabrication process of the device and its
real-time operating state (temperature) at a given frequency.
3.1.2.3 Dynamic Power Switching
Like DVFS, dynamic power switching (DPS) is a power-management technique that reduces active power
consumption of a device. However, whereas DVFS reduces dynamic and leakage power consumption,
DPS reduces only leakage power consumption, at the expense of a slight overhead in dynamic power
consumption.
With DPS, the system switches dynamically between high- and low-consumption system power modes
during system active time. When DPS is applied, a processor or system runs at the highest OPP
(maximum frequency and voltage) to complete its tasks quickly, followed by an automatic switch to a
low-power mode for minimum power consumption. DPS is useful when a real-time application is waiting
for an event. The system can switch to a low-power system mode if the wake-up latency conditions allow
it.
This technique consists of maximizing the idle period of the system to reduce its power consumption.
Figure 3-3 compares energy consumption with and without DPS.
Figure 3-3. Comparison of Energy Consumed With/Without DPS
Normalized power
1.0
0.5
0
With DPS
Transition
overhead
1 2 3 4 5
Execution time
Energy consumed = 1.15 J
prcm-003
Figure 3-3 compares the power consumption behavior for the same device operation without DPS (left
side of the figure) and with DPS (right side of the figure). When operating without DPS, the device has a
constant leakage current in idle mode. By using DPS, the system reduces the leakage current to zero.
However, the transitions between system power modes can require storing the information before entering
a low-power inactive state and restoring the information after a wake-up event (see Figure 3-3). This
results in additional dynamic power consumption, referred to as the transition overhead, (see Figure 3-3).
Transition overhead must be considered for a DPS operation.
For efficient deployment of DPS techniques, it is necessary to dynamically predict the performance
requirement of the applications running on the processor. The DPS controller must account for the
overhead of wake-up latencies related to domain switching and ensure that they do not significantly affect
the performance of the device. Even with transition overhead, however, the user can identify an optimal
idle-time limit after which the DPS is useful for dynamic power-saving.
3.1.2.4 Standby Leakage Management
Standby leakage management (SLM) is a power-management technique that reduces standby power
consumption by reducing power leakage.
226 Power, Reset, and Clock Management SPRUGN4L–May 2010–Revised June 2011
Copyright © 2010–2011, Texas Instruments Incorporated