[Gta04-owner] Power supply for internal USB PHY
neilb at suse.de
Thu Jan 17 01:51:41 CET 2013
I've been exploring the possibility of enabling "off-mode" for the OMAP3
which hopefully will save a bit of power. It mostly works, however the two
USB ports (internal and external) don't survive the transition through off
As a result of raising this issue - of the internal USB particularly - on
the linux-omap list, it seems that it might be necessary to power-cycle the
internal USB transceiver (USB3221). You can read the thread starting:
The best explanation that I can come up with is that when the 'CORE'
power-domain of the OMAP3 turns off and comes back on it loses sync with
the USB phy in a way that 'reset' is insufficient to fix and a power-cycle
is needed. Seems strange and I'm not completely certain that this is the
case, but the evidence seems to point that way.
So it appears that it would be useful to be able to independently
power-cycle the USB phy in much the same way that you can now power-cycle
As I say, I'm not completely sure so this isn't yet a "must have" for the
GTA04a5, but it could be useful if it isn't too hard.
On a related topic, my reading of the documentation for the USB3221 suggests
that the VDD3V3 pin is a power *output*, not a power *input*, whereas the
schematics show it wired like an input for the GTA04a. I wouldn't
expect this to be a serious problem, but it seems wrong and could possibly
cause an unexpected power leakage.
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