Magic Blue Smoke


Voltage/Frequency Scaling Mechanisms

I was in Boston last week attending SNUG and got a chance to interact with many designers and one of the key concerns raised were in understanding the Voltage scaling approach . Planning to take a quick tour on this topic in my next few posts

There are various voltage scaling approaches that are in use today

Static Voltage Scaling: Different blocks in the design will be operating at different fixed supply voltages

Multi-level Voltage Scaling: An extension to static voltage scaling where in different blocks are switched between two or more voltage levels.

Dynamic Voltage and Frequency Scaling : An extension to Multi-Level Voltage Scaling Voltage levels are dynamically varied as per the work-load of the block

Adaptive Voltage Scaling : An extension to  DVFS and its a closed loop representation of the above method. Power Controller block within the design adopts itself dynamically to varying work-loads.

DVFS example: Here is an outline of tasks that will be executed within a design to scale voltage and frequency dynamically, controller first decides the minimum clock speed that meets the workload requirements. It then determines the lowest supply voltage that will support that clock speed. Given below is an example of a sequence thats followed  if the target frequency is higher than the current frequency

— Controller monitors the variance in work-load
— Controller detects variation in work-load and programs the device to operate at different voltage
— Block under question continues operating at the current clock frequency until the voltage settles to the new value
— Controller then programs the desired pre-determined clock frequency

Varying clocks and voltages during operation is  a new methodology in the design and leads to many challenges in the design process

— Identifying the optimal combination of Voltage/Frequency
— How to model the timing behavior
— Clock and Power Supply locking times.