Power Efficient Software Coding

Question

In a typical handheld/portable embedded system device Battery life is a major concern in design of H/W, S/W and the features the device can support. From the Software progra

Answer 1

Zeroith, use a fully static machine that can stop when idle. You can't beat zero Hz.

First up, switch to a tickless operating system scheduler. Waking up every millisecend or so wastes power. If you can't, consider slowing the scheduler interrupt instead.

Secondly, ensure your idle thread is a power save, wait for next interrupt instruction. You can do this in the sort of under-regulated "userland" most small devices have.

Thirdly, if you have to poll or perform user confidence activities like updating the UI, sleep, do it, and get back to sleep.

Don't trust GUI frameworks that you haven't checked for "sleep and spin" kind of code. Especially the event timer you may be tempted to use for #2.

Block a thread on read instead of polling with select()/epoll()/ WaitForMultipleObjects(). Puts stress on the thread scheuler ( and your brain) but the devices generally do okay. This ends up changing your high-level design a bit; it gets tidier!. A main loop that polls all the things you Might do ends up slow and wasteful on CPU, but does guarantee performance. ( Guaranteed to be slow)

Cache results, lazily create things. Users expect the device to be slow so don't disappoint them. Less running is better. Run as little as you can get away with. Separate threads can be killed off when you stop needing them.

Try to get more memory than you need, then you can insert into more than one hashtable and save ever searching. This is a direct tradeoff if the memory is DRAM.

Look at a realtime-ier system than you think you might need. It saves time (sic) later. They cope better with threading too.