So, this board takes 90mA in full-speed run mode. That's not better than Raspberry Pi Zero (despite pico having 2000 times less RAM, and 10-20 times slower CPU). So why would one use this over Zero? Am I missing something?
A microcontroller like this should be able to sleep for microseconds at a time or possibly even less (but you can obviously sleep for long periods of time too), letting you spend the majority of every second asleep, just waking up for brief instants throughout the second (possibly thousands of times) to do work. This enables huge power savings over something like the Pi Zero.
You can also run the microcontroller at a lower clock speed to save more power, if you don't need to run at maximum speed to get things done.
I would be curious what process node this microcontroller is built on, because I completely understand why these numbers would be discouraging when the microcontroller is running at full tilt.
Microcontrollers allow much lower system complexity, more predictable timing and real-time response times, and nearly instant boot times.
Virtually every USB port can supply at least 100mA, so for most applications there’s no difference between using 9mA or 90mA. That said, if you’re making a battery project you’ll almost certainly be able to stretch the microcontroller further. Micros generally have fantastic support for low power sleep modes.
I would add that it really depends on the problem you're trying to solve, though. Microcontrollers are disadvantaged compared to Linux SoCs for many workloads other than low power and low latency (i.e. hard and soft realtime).
Keep in mind that's at maybe 2 volts rather than 5 volts. Still, it's 360uA per MHz, counting the two 125MHz M0+ cores as 250MHz total. That's pretty power hungry compared to other Cortex M0+ products which tend to be in the 100uA/MHz range. I think the real product here is the RP2040 SOC and the Pico board is described as a breakout board for it. I like to think the RP2040 will find its way onto future RPi Linux boards, to give them some analog and realtime capabilities.
That said, your point about power is well taken. I haven't looked at the Pico. What is the power draw in sleep mode?
0.006W from memory. But do not trust me. Watch the video.