I want to build a linux(yes i want linux specifically or a deritive of it) smartwatch as a prototype that lasts ~24 hours. Ive been looking for chips that are small and power effient enough but most of them cant run linux. If i have a 400mah battery that gives me a power budget of about 60mw… I know its possibly because there are wearos(basically android) watches that last 3-4 days. I dont know what kind of sorcery that is but that means it consumes about 15mw??? I really do feel like im miscalculating something but i checked multiple times. Do they hibernate linux/android and run it off of another chip. I also dont know how to excecute that properly and its kind of off topic of my question. So point is linux on a ~60mw budget in s smartwatch. I want to use a mip display as i really like the look and it uses little power but if ever want a heart rate sensor in it thats even more power consumpotion. Thanks in advance i guess if a saint answers this shitstorm of a question.
You will have a hard enough time just finding a SOC that you can get documentation for without signing and NDA and promising to buy massive quantities of them.
I thought of getting a low power arm cpu like the one in the raspberry pi zero 2 or something less powerfull and then use the rp2040 as a coprocessor. The rp2040 only uses a few ma so its a good choice and i could use interrupts to wake the main cpu. I can also put the rp2040 into sleep and only operate the screen and that would basically be a normal watch and it would last for months.
That’s a lot to fit in a watch. The PCB layout will be difficult and the requirements for it will likely exceed what the usual prototype PCB manufacturers can produce.
The RP2040 is a power hog. It takes 180µA in its lowest power sleep mode. There are other microcontrollers that can be in run mode and use less power than a sleeping RP2040. I would suggest looking into some of the STM32L series microcontrollers. They can get down into the nanoamp range in sleep mode and run less than 100µA/MHz.
Thanks for the suggestion but of course ill look into what mcu i want better when it comes to that. A larger pcb at first doesnt bother me that much but i want to get down to watch size in the far-future. This is only a hobby project so nothings set in stone. Im also working on a flashlight right now so im balancing these two projects.