the root cause of flip-flop charging logic if you insert wall charger

matt_hsu matt_hsu at
Thu Sep 18 07:47:28 CEST 2008

Werner Almesberger wrote:
> Andy Green wrote:
>> | The root cause is the signal from VBUS rasies and drops rapidly when
>> | inserting a wall charger.
> [...]
>> It sounds like you were already in Linux doing this, so I wonder what is
>> the excuse of the adapter now to drop dead briefly on insertion?
> Is this VBUS coming out of the adapter (i.e., measured on the adapter's
> cable) or VBUS obtained by the system,
I'm not sure of this. I measured it from USB1/USB2 which is connected to 
Do you think this elevator-style-signal is caused by system?
>  i.e., subject to contact bounce
> and all that ?
> Still, USB detection has a fairly generous debounce time of 62ms, which
> should be sufficient.
Yes. But the USBx ping voltage raises/drops over 62ms, according to the 
following pics.

The time dimension is 500ms.

> By the way, Matt, I didn't see your original mail. Could you perhaps
> post it here with the pictures (or, if they're too big, put them on
> sita aka people) ?
> - Werner

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