01-31-2022, 12:42 PM
(01-31-2022, 10:09 AM)grump_fiddle_reinstall Wrote: OK so if I understand correctly, the phone battery discharges as the connection between it and the keyboard battery is limited to 500 mA. So even though there is enough juice in the keyboard battery and the keyboard battery is connected to a mains charger the phone battery discharges.
It is not really the connection what limits the current (it is mostly depends on the width of PCB traces) but the USB specification itself.
For an USB 2.0 port, basically a device can draw up to 500 mA of current and not more (otherwise it may cause problems like blowing a fuse or overdrive PSU).
So this is where charging protocols may come up or at least charger should tell the phone somehow if it can provide higher current.
However, keyboard only has five connectors - SDA/SCL/VCC/GND/INT, so basically it can not communicate directly with charging controller.
So that is what can be overridden by the method above, but not for any power sources which can not provide this amount of current.
That means a real solution would be an automatism... I don't know what is the internal schematics of keyboard, so what information of its microcontroller has.
Ideally, it may has some information which may be communicated towards OS.
...or at least OS knows keyboard is attached and if it is, it may set higher current rate when current limit is set to 500 mA.
However, it is also an interesting question what happens if phone's own USB connector is powered but it depends on the circuit(s)... it may has to be handled somehow even if this scenario is not supported... (I hope internal PSU may not overrun this case).
