[Gta04-owner] USB questions

Andreas Kemnade andreas at kemnade.info
Wed Mar 14 09:22:07 CET 2012


Hi,

I have some questions regarding USB.

1. The most critical thing and the most annoying problem with the GTA04 in
general is the fact that GTA04 does not cope with power supplies which cannot
provide the full current at some time. Voltage breaks down and the GTA04 does 
not use the power supply at all. So the voltage goes up again. Seen with 3.2
kernels and 2.6.32. In contrairy GTA02 does not stop drawing power in such 
situations. What can be done here? Simply ignore VBus disconnect events 
(perhaps until iD is low)?

2. The usb mode sysfs control does not evaluate what is written to it or
am I missing something? (in both 3.2 and 2.6.32). What's going on there?
in musb_core.c the platform mode callback is called is called and passed on to
but in musb/omap2430.c musb_platform_set_mode() does not evaulate the mode
parameter.

3. In 2.6.32 there is code in otg/twl4030_usb.c commented out dealing with
the OTG_CTRL_DRVVBUS because it is done in mbus. But I cannot find it there.
Where is it done?
Anyway I found out that clearing DRVVBUS after ID is pulled low gives the
opportunity to use it as unpowered and so you can reuse stuff like old special
cables created for GTA02 (including USB hubs giving out power to the host side)
 if ID pin is low.

Greetings
Andreas Kemnade
PS: I have not forgotten that si4721 stuff.
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