Battery powered linux product suggestions? - Page 1
Forum section: electronics / general

author: t-ray
author_rank: Newbie
timestamp: August 11, 2017, 11:12:08 pm
content: Hi forum! I'm curious if anyone has suggstions for a processor (module prefered) that runs Linux (can be very minimal) that would make sense to put in a handheld battery powered device. Imagine something like standard DVMM (I know its Dave's favorite topic) and has a battery life of say 100hrs on 2x AA's.To be specific20-30mW Average PowerVery idle, update segmented LCD or dotmatrix LCD every second or so but still "on" (could be sleeping though..)Small amount of background tasks (ADC's, I2C, SPI)BT 4.0+Segmented LCD of graphic displayUSB but off/idle at this power levelThe resononing is its a thing that would be doing the above slow things 98% of the time. But the other 2% a much higher end device that could say serve a basic web page or have very flexible USB (keyboard, flash drive, etc) and maybe regular video out (VGA, HDMI). This 2% of the time could be while its powered by something else.I keep thinking smart watches but I'm not sure if those run linux or just a low level RTOS. And a custom CPU is not really an option.Any suggestions? I know this is probably shooting for the moon but figured I'd ask anyway.TIA,T-Ray

author: tszaboo
author_rank: Super Contributor
timestamp: August 11, 2017, 11:20:32 pm
content: Nope. DDR memory alone is a huge power hog. Any kind of DDR memory. We are talking about 200mW-0.5W for a small memory chip, just on standby. Maybe with some exotic components like PCM, but those are unobtanium.There is one or two order of magnitude power consumption difference between a MCU and an MPU.

author: ejeffrey
author_rank: Super Contributor
timestamp: August 13, 2017, 02:29:40 am
content: There are ways to do this, but it is hard -- it takes a lot of work both in hardware and software to get a system that is functional, powerful, and low power.Maybe a good example to think of is the Amazon Kindle. According to this page:http://www.devicespecifications.com/en/model-cpu/92752e19It has an ARM Cortex-A8 class CPU, yet lasts for weeks or months on a charge.Those specs list 256 MB of RAM. Thats enough to run Linux, although I don't know what the Kindle does. Of course this will be some low power ram (LPDDRX takes much less power in "suspend mode"), but even that doesn't get you the kind of lifetime the kindle has. Probably it uses a combination of techniques: a low power microcontroller that can take over some tasks without waking the application processor, and an OS optimized for instant-on so that it can go into a super-low power mode that shuts off RAM refresh, yet recover quickly when the user demands it. Many (most? all?) ARM application processors have the ability to configure the CPU cache as an SRAM that you can execute from. This can allow you to have a minimal execution environment for simple tasks without powering up the DRAM.So these techniques can all limit the standby power, but remember that all of the code that runs in the MCU, or is executing from cache in the APU don't have the benefit of the full Linux environment. As you move more and more of the everyday functionality into those reduced power enviornments, you are going to wonder if it is actually worth the trouble to have the applications processor at all. I am the guy who thinks it is silly how people like to use tiny microcontrollers in non-power and space constrained applications, then faff around with 1980s style C, and then worry about running out of their 8K of RAM when they could just use a bigger processor and written their code faster and more functional. But battery powered application processors are hard.