Hello Everyone!
I would like to ask you about your experiences with using different SBCs/SOMs on battery power. First thing I'm interested in is possibilities to reduce power consumption while running (in idle mode, with disabled unnecessary peripherals), doing reliable suspend/resume and proper system shutdown and also time needed from powering up device to start kernel boot. The other things that would be nice to have integrated in such systems are battery charger and power switches. Also it would be nice to have device-tree compatible kernel. Most of popular boards (such as Raspberry Pi and most of Orange Pi) are based on set-top-box dedicated chips which have not almost any power management beside frequency scaling. I played a little with these boards:
- Raspberry Pi - everyone knows, no sleep mode, no proper shutdown, older versions even didn't have SMPS so it's not the best choice for battery powered device. The one advantage (beside of the biggest community and available articles base) is that you can build really fast booting system with buildroot.
- Orange Pi Zero (and probably other Allwinner H2/H3/H5 boards) - pretty powerfull, can be put to sleep but power consumption reduction is not great - at least on their Armbian system, I didn't dig deep into kernel and don't know if PMIC is controlled properly. But waking-up (or even booting-up) is not reliable.
- Orange Pi i96 - even less documentation and community which is sad because RDA8810PL looks perfect for battery powered, compact device - this is the REAL system on chip with RAM, ROM and power management integrated in single package and there are even programmable regulators on chip but not available outside of the board. Can run on li-ion cell but does not charge it - it looks like some components are missing. Does reliable sleep/resume (with additional wakeups at random) but does not boot from every sd card and I failed with flashing Linux to on-chip flash. Also shutting down does not work well - it goes to the state in which it consumes more power than running. Non-mainline but open source kernel - unfortunately does not support DTB and looks a little bit hardcoded for particular configuration - for example if you turn off V4L support it won't even compile. Also as far as I know there is no hardware SPI/I2C support - everything had to be done with bit-banging which can have impact on performance for example when working with SPI display. And biggest fail is no reset button/pin/whatever - especially irritating when you have battery soldered to the board
Both orange pi boards have on-board wifi but not very usable - big latencies and random disconnects.
- Arietta G25 - Atmel SOC with ARM9 so a little bit older hardware but really nice form factor, documentation available, mainline kernel with DTB and buildroot support out of the box, no binary blobs, reliable sleep with waking up from gpio or rtc
- Lichee Pi Nano - also ARM9 but from Allwinner, only 32MB RAM (integrated with CPU), very nice form factor, very cheap but absolutely any English docs or community. With help of Google translate you can read some rudimentary documentation and one Chinese forum where people are working out things for variety of operating systems. I failed with making my own kernel+buildroot with their instructions but it looks possible, prebuilt Linux boots, sleeps and resumes rather reliable. There are also development of other systems such as Micropython and xboot which work but does not support sleep mode. Especially xboot with it's small footprint, lua scripting, modularity and support of hardware configuration similar to devicetree - where you can very precisely set up peripheral power management and clocks - looks great for single app device but lack of sleep mode limits its usability.
I did some measurements of power consumption that are not honest and systematic in any way (and not necesserily were made in optimal configurations) so I won't write numbers here but above they are ordered from higher to lower consumption in sleep mode.
I didn't test yet any i.MX and OMAP board - these CPUs are used in some pretty well power optimized devices and looks well documented but boards are more expensive than RasPi or Chinese SBCs so it would be nice to read some opinions before picking up one.
