Maximizing Battery Life

Hi,

Just noticed jacobbeningo's excellent post (10 Tips for Maximizing Battery Life)  in Embedded on Maximizing Battery Life. Some really good advice which any designer should take note of. Thanks, Jacob!

This is a subject I've spoken on many times at conferences over the years. For many systems, battery life is the most important driver in the design and it's going to become more important as time goes on. Mirroring Jacob's excellent approach, my tips would be as follows...

#1 Minimize memory access

It is well known that memory access consumes significantly more energy than executing instructions. An instruction involving an external memory access can consume an order of magnitude more energy than one which doesn't. This is really the big elephant in the room when it comes to being frugal with energy. There is also a clear hierarchy in how much energy it takes to access different types of memory. register accesses are obviously cheapest, followed by on-chip RAM, then cache, then external memory. So, consider:

• how efficient are your data structures?
• how well do you make use of cache (cache accesses are much cheaper)?
• is there an area of on-chip SRAM which you can use (usually much faster as well as more energy-efficient)?

#2 Minimize instruction count

Executing instructions may be unavoidable but each instruction consumes energy. There is a lot you can do to minimize the number of instructions executed by your program, ranging from making sure you have the right compiler options (correct target system/architecture, optimize for speed etc) to choosing the right algorithm for the job.

#3 Make as much use as possible of power saving modes

Here, Jacob and I are on the same ground. All ARM-based systems include a range of power saving modes - it's built into our DNA! The chip implementers work very hard to ensure that the microarchitecture supports them as much as possible, with multiple clock and power domains etc. But if the software developers don't use them, they're wasted! The goal for any frugal software application must be to spend as much time as possible in as low power a mode as possible. Make sure you understand the modes supported by your chosen device and architect your system to make maximum use of them.

There are lots of other considerations as well and I'm presenting on just this subject at TechCon in a few weeks time. If you're interested in the subject, it would good to see you in the session.

Chris

ARM at ARM TechCon