USB power switch not enabled

[wad]

On the XO-1.5 prototypes, the USB power switch is not being turned on (by either OFW or Linux.) I'm using version Q3A03 of firmware.

The work-around is to place a zero-ohm resistor at R155, shorting around the USB power switch.

The signal which should be used to enable this power is GPO10 (pin AL18, NOT GPIO10) on the companion chip (alternate function is USBD_PDN#). This signal should be asserted (active high) to provide power to the USB ports.

Note that the power supplied to the USB ports on A1 prototypes is minimal (< 0.3A) due to undersized traces, fixed in later versions.

[wmb@…]

OFW already attempts to set GPO10 to high, and has done so since the early bringup versions. According to my reading of the registers, it appears that GPO10 should be high. I guess we need to probe the net and see what is going on.

[wmb@…]

Wad verified that - at least on one board - the net goes high when OFW starts.

I'd be rather surprised if Linux changes it...

According to the 855 data sheet, the GPO10 pin defaults to 0 after resume, so we need to verify that the setting is correct in that case.

[cjb]

USB works under Linux too, so closing this. We don't know what'll happen with overcurrent.