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I think waking up in itself is expensive, regardless of what is actually done after.
Not really. The CPU needs to wake up all the time to keep Bluetooth protocol happy so waking/sleeping is fast and is not an issue. nrf52 can last months from coin battery sending advertising packets every few hundred of milliseconds which wakes up CPU and radio for every packet.
So it definitely depends on what is actually done after waking and for how long. The power is drawn by CPU being busy running code or by some other hardware which is not put to sleep . Bangle running any JS code from flash storage makes CPU and SPI flash chip busy. Drawing to display keeps CPU and display busy.
fanoush
@halemmerich
I think waking up in itself is expensive, regardless of what is actually done after. So refreshes every second are 60 times as expensive as doing that only every minute, in regard to the cost of waking the processor from sleep. Drawing to the screen is relatively slow and I suspect it keeps the processor awake that whole time.
drawImagesdocumentation says it should render "only" the rectangle that is needed to cover the images, but that seems to be all pixels of every used image so it will probably only save relevant amounts of time if the images are small. Updating only changed pixels would need some way of a fast check for change between what will be drawn and what is on screen. I do not think that exists in a way that is faster than just rendering all pixels.