At Fri, 9 Aug 2019 17:01:28 -0400 [email protected] wrote:
>
>
> Robert,
>
> If you have a look at the Pocketbeagle schematic, you can see what happens
> with the USB connector, which comes in on page 2. Power on that pin goes to
> VIN.USB, which goes straight to (page 3) the Octavo OSD3358 VIN_USB pins.
>
> You can look at the Octavo datasheet [1] - it's for the OSD335x_SM - they
> tell you almost nothing. The only partly useful thing they tell you is "The
> OSD335x-SM may be powered by any combination of the following input power
> supplies. Please refer to the TPS65217C datasheet for details." The
> smartest thing to do would be to map the pins to the chips they are
> connected to using Octavo's tool [2] and the TI datasheets. I'm certain
> there's no isolation, but there is a switch to enable one or the other
> inputs (perhaps you had a looser definition of isolation in mind). Figure
> 11 on page 27 of the TPS65217C datasheet [3] should show you what that
> looks like. These are configured by the PPATH register in [3], which I am
> not precisely certain how it is configured in the first place, but you
> should be able to modify it on I2C0 (I think).
>
> All that said, it looks to me like it's fine to do. But I feel like I've
> done this and had some weird results, I just can't remember exactly what
> they were. I think the results included unplanned reverse power flow (USB
> charging other things connected to the same VIN power supply), the device
> not shutting down exactly as I expected, and similar behavior. I don't
> think we smoked anything, though, so there's that. Worth looking through
> that data sheet a little to make sure you're happy first.
OK. The reason I want to know is that I have an expansion board that supplies
power (and does other things). It does have a serial console header, so I can
connect a TTL serial<=> USB cable for debugging, but unless I really want to
raise XModem (from the dead?) there isn't any way to do something like
download a fresh executable program ("cross" built on a RPi). I just wondered
if it is "safest" to just unplug the Pocket Beagle from the expansion board
and tether it to my laptop and use the Tcp/Ip over USB to do the "large"
transfers of things like exe files, etc. This is what I have been doing and
was wondering if I really have to do it that way or if I can plug in the USB
while the Pocket Beagle is still being powered by the expansion board.
>
> I would be quite interested to know precisely where PPATH is configured,
> beyond its default settings. It may be in the uboot source which is not [I
> think] in the BB distributions. That stuff isn't bad to look at, and I was
> going to, but for the life of me I can't remember where I built that and I
> can't find it right now. Robert also has a few scripts in /opt/scripts/boot
> which configure a LOT of things, I've only scratched the surface trying to
> understand them.
>
> [0] -
> https://github.com/beagleboard/pocketbeagle/blob/master/PocketBeagle_sch.pdf
> [1] - https://octavosystems.com/docs/osd335x-sm-datasheet/
> [2] - https://octavosystems.com/app_notes/osd335x-family-pin-assignments/
> (search for VIN_USB)
> [3] - http://www.ti.com/lit/ds/symlink/tps65217.pdf
>
> Hope that helps. I have nothing to do with the pocket beagle but I did spin
> a couple boards based on it and the octavo RED board.
>
> Best,
>
> Jim
>
> On Fri, Aug 9, 2019 at 3:33 PM Robert Heller <[email protected]> wrote:
>
> > If I am applying a 5V power supply to the Vin pin (P1-1) of a Pocket Beagle
> > (say from an expansion board that includes a power supply), is it safe to
> > also
> > plug in a [powered] micro-USB cable? That is, does the Pocket Beagle have a
> > power protection / isolation circuit?
> >
> > --
> > Robert Heller -- 978-544-6933
> > Deepwoods Software -- Custom Software Services
> > http://www.deepsoft.com/ -- Linux Administration Services
> > [email protected] -- Webhosting Services
> >
> >
> > --
> > For more options, visit http://beagleboard.org/discuss
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> > .
> >
>
--
Robert Heller -- 978-544-6933
Deepwoods Software -- Custom Software Services
http://www.deepsoft.com/ -- Linux Administration Services
[email protected] -- Webhosting Services
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