[Gta04-owner] Connecting USB-Stick

NeilBrown neilb at suse.de
Mon Sep 17 23:41:40 CEST 2012


On Mon, 17 Sep 2012 22:19:04 +0200 Christoph Mair <christoph.mair at gmail.com>
wrote:

> Hi Sven,
> 
> On Mon, Sep 17, 2012 at 10:14 PM, Sven <openmoko at maricon.de> wrote:
> > Another question:
> > Is the limitation to 100mA due to hardware or to software? Or in other
> > words: Would it be possible that QtMoko throws a question directly after
> > booting, something like: "You connected an USB device that requests 200mA.
> > Do you want to provide this with regard to your battery lifetime?"
> 
> Unfortunately this is a hardware limitation and I'm don't know an easy
> "fix" for it yet.

Yes and no...

The "software" in the USB stick claims that it needs 200mA.
The software in the GTA04 reads this, determines that 200 > 100, and so
refused the enumerate the device.

When I was testing, I hacked that last test so it would enumerate the device
anyway, and I managed to mount the USB stick.
So presumably the GTA04 actually delivers enough current for this particular
USB stick to actually work - at least some of the time.

If you used the USB stick in a way the required lots of current - maybe wrote
many 100s of megabytes to it - it could possibly fail to write successfully,
or might even fry your GTA04 (depends on whether there is effective current
limitation ... I suspect there is).

If you want to try (and risk harming your USB port) I can point you to where
you can try hacking the code...

(look for 
	.power		= 50,			/* up to 100 mA */
in arch/arm/mach-omap2/usb-musb.c, but don't say that I send you.
Note that the units of power are "2mA".
)

NeilBrown
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