Arduino for STM32

Below 4.2v, I can pretty much leave it to change. When it reaches 4.2v I can kind of 'pwm' it to mimic a reducing current charging say for an hour and finally off. I think you haven't read charging algorithm.... You need to limit voltage to 4.2V and reduce current when below 4.2V. When charging vol...

I use this bootloader and there are no errors.
I got .bin file from this link:
https://github.com/Serasidis/STM32_HID_ ... -670308140

I wrote simple program for testing digital IO speed. For read tests it's using 2 different pins (PA1 and PB1). This it what I get (-O3 fastest optimization): Port I/O speed test. Arduino digitalRead/Write / digitalReadFast/WriteFast / STM32 register ********* Write test: ********* digitalWrite: 1853...

I found (using an oscilloscope) that the reaction time to a repeating pulse from a Nano is very 'juddery' and varies between: 1.7uS to 3.8uS using Method A (digitalRead) and 1.0uS to 2.6uS using Method B (digitalReadFast) Is this what you would expect? Am I doing something fundamentally flawed? Hav...

I think that every thing is quite clearly explained on the site you linked. All pins with same number are connected to line with same number. They are multiplexed to one line. IMPORTANT: You can not use two pins on one line simultaneously: PA0 and PB0 and P C0 and so on, are connected to Line0, so y...

Charging li-ion algorithm is pretty simple and you can find it on many web sites.

You could use STM32 as uC for a charger but you'll need few more elements. Li-ion batteries are charged using CC/CV method, so you need to control voltage and current.
But it's easier to use dedicated uC (eg. TP4056)

Those might be magnetic encoders.

... analogWriteResolution(16) + analogWrite() command still have only 12-bit resolution. ... I don't know why, by analogWrite resolution is limited to max ADC resolution. wiring_analog.c void analogWriteResolution(int res) { if ((res > 0) && (res <= 32)) { _writeResolution = res; if (_write...

If you use built-in RTC and board like blue pill, then remove PC14 and PC15 pins.

Yes. If there is no support in Arduino compatible libraries you can use HAL or LL libraries.
Here's link to stm32duino Wiki:
https://github.com/stm32duino/wiki/wiki

And for API references:
https://github.com/stm32duino/wiki/wiki/API

Interrupts, DAC you can use same way as with Arduino boards.