folks, as you saw a couple months back we have an issue with the EOMA68-A20 CPU Card where [without authorisation] some changes were made to the power distribution by the ODM. i still haven't worked out if those changes were/are a blessing or a curse.
a reminder of the issue: they connected the ACIN *directly* to VBUS on the USB-OTG input, removing the usual safety and detection features (a SY6280 plus use of some GPIO) which allow programmable (or AXP209-controlled at least) switching between USB-OTG power and 5V input power.
i have this sneaking suspicion that the solution might actually be staring me in the face, so wanted to run it by people, see what they thought. what i *believe* the solution is, is to simply move that USB-OTG/5V detection circuitry (in this case a SY6280 plus use of some GPIO) onto the I/O boards, and to effectively treat the EOMA68 5V power "as if" it was a USB-OTG two-way power system.
so rather than have in the spec "you must provide 5V power", change that to "you must imagine that the power circuits are identical to what you'd normally have to do for USB-OTG". which, because wits-tech directly connected the bloody USB-OTG power to the ACIN by fusing the pins together at the AXP209 is actually exactly how it is.
the advantage of this change (i say change, it's more like being frog-marched unwillingly towards a solution...) is that if people happen to accidentally plug in the CPU Card into a USB-OTG socket and keep it powered up, then
a) the CPU Card will survive unplugging and can transition happily from one chassis to another
b) as long as it doesn't draw too much current it would be possible to power a portable device *from* the USB-OTG... or at least charge its battery (if it has one)
c) i'm sure there's something else...
anyway i *think* it's a blessing - it would just have been nice to have been consulted by the ODM, eh?
if anyone's got any other suggestions on how to manage USB-OTG power switching it would be very helpful to hear them: i will put them into the EOMA68 spec as implementation guidelines.
l.