SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
Dynamic voltage and frequency scaling (DVFS) consists of minimizing the idle time of the system. The DVFS technique uses dynamic selection of the optimal operating frequency and voltage to allow a task to be performed in the required length of time. This reduces the active power consumption (power consumed while executing a task) of the device while still meeting task requirements.
The values in Figure 3-16 are hypothetical. They are meant only to clarify the concept and do not represent valid test results on the device.
Figure 3-16 shows the DVFS technique by comparing a process executed at maximum frequency and operating voltage without applying DVFS to the same process executed at optimal frequency and voltage using DVFS, based on the task requirements. If a task that must terminate in 4 seconds is performed at maximum operating frequency (see the left side of the figure), it terminates in 1 second, and the remaining 3 seconds are spent in idle mode.
With DVFS (see the right side of the figure), the operating frequency is reduced to optimal level; the task takes the full 4 seconds to complete, but power consumption is reduced. In addition, the voltage can be reduced further to save power so the dynamic and leakage power consumption are reduced.
DVFS requires control over the clock frequency and the operating voltage of the device elements. By intelligently switching the individual elements of the device to their OPPs, the power consumption of the device for a given task can be minimized.
For practical reasons related to the development of the device (flow, tools), DVFS can be used only for a few discrete steps, not over a continuum of voltage and frequency values. Each step, or OPP, is composed of a voltage (V) and frequency (F) 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.
When applying DVFS, a processor or system always runs at the lowest OPP that meets the performance requirement at a given time. The user determines the optimal OPP for a given task and then switches to that OPP to save power.