force usb charge current

Andy Green andy at
Tue Jan 27 18:47:11 CET 2009

Hash: SHA1

Somebody in the thread at some point said:
| Hi,
| I can force charge current to 100mA / 500mA / 1A  via
| /sys/class/i2c-adapter/i2c-0/0-0073/pcf50633-mbc/force_usb_limit_dangerous
| .. but I find it a bit too coarse grained...
| Is it possible to set allowed current to arbitrary value, or at least
| 350mA or 750mA ?

Well, the short answer is "no" but it's actually an answer to the
question you didn't ask.

We can set charging current in a finegrained way.  But, what we actually
need to set is the USB connector current limit regardless of where the
current is used.

If we set charging current then the actual current at the USB connector
is going to be that current, plus whatever else is used by backlight or
CPU or whatever.  How can we compute the charging current then?

There is a global "at the USB connector" current limit, but it only has
those steps, 100, 500, or 1000mA.

You could add ability to force max charging current separately, and
estimate a maximum current for "everything else" but it doesn't seem
like a good idea to me when WLAN can add >100mA, GSM unit might decide
to do something, etc and you only had a budget of 350mA to start with.

- -Andy

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