[U-Boot] [linux-sunxi] A20-olinuxino-micro hangs in U-boot if powered from MINI-USB only.

[Nikolai Zhubr <n-a-zhubr@yandex.ru>]

Hi,
24.12.2018 22:54, John S:
> On Monday, 24 December 2018, 19:10:24 GMT, Nikolai Zhubr<n-a-zhubr@yandex.ru>  wrote:
>>> Hi,24.12.2018 20:32, Diego Roversi:
>>>> I'm observing that the said A20-onlinuxino-micro board hangs in U-boot
>>> in probing USB2 (see example below) in case it is powered by connecting
>>>
>>> I think it's normal. During the boot, u-boot initialize the usb otg, and for a
>>> fraction of second the power is disconnected. I solved it by attaching a
>>> battery (and I have a PSU as a side effect :) ).
>
>> Ah, got it. Thats a funny issue then. Its not the software to blame. Ok.
>> (Ideally, this peculiarity should probably have been mentioned by Olimex
>> in their docs, but maybe I've overlooked it.)
>> Solved it for now by disabling USB altogether.
>
> Isn't it caused by the software as stated above, i.e. nothing to do with Olimex?

Well, IMHO is has to do with Olimex because they designed this specific 
circuitry, and the circuitry is such that 5V voltage constantly applied 
to the micro-usb connector might essentially become disconnected (at the 
board side) by programming -- if I understood it correctly. I suppose 
this certainly could be prevented in hardware, by e.g. just wiring the 
5V usb line to a power unit through a diode, whatever, unless it is 
prohibited by some sort of usb compatability requirements. I don't know 
if it would be good though. Of course the effect is caused by software 
in some sence, but the software can not know that there is no other 
power supply line present when it probes this usb port? Or could it 
indeed? I'm not sure if AXP state could be somehow probed to do a 
workaround, in theory, but that would be an extreme overcomplication anyway.


Thank you,

Regards,
Nikolai



>
> John
>