If it is of any interest, the splitter cable works and we can connect our full-speed device without a hub. If you can get hold of a solderable mini A or mini B plug, it is relatively easy to make such a cable from a regular A-to-miniB cable.

Some important points however:
1. The plug that goes into the OTG port must have its ID pin grounded such that it is detected as a ‘mini A’ plug. We actually used a mini B plug but that doesn't matter as long as its ID pin is grounded. It was difficult enough to find solderable mini B plugs already, mini A plugs are extremely elusive.
2. The mini A plug must be plugged into the OTG port at boot! Nothing needs to be attached to it, but the plug itself must be connected to activate the OTG port. Once the Overo has booted with the plug connected, it can be disconnected and reconnected at leisure.
3. This splitter cable hack works in our case because the device does not perform power negotiation. If it would have told the USB port that it needs 400mA, the OTG port would say “no go” and shut down because it does not know that the device gets its power from elsewhere. There are hacks to disable this check but because the 100mA limit is a real hardware limit, it should not be tampered with unless you know what you're doing.

It seems USB can be tamed on the Overo with the right strategy, yet it would have been much more convenient if a full-speed PHY had been included for the A host port and if proper hot-plugging had been supported…

Alexander

On Thu, Jul 28, 2011 at 5:54 PM, Alexander Thomas <alexander.thomas@esaturnus.com> wrote:
I found in the TPS65950 manual:
“The USB PHY supports the 3-pin DAT-SE0 and 4-pin VP-VM modes of the CEA-2011 specification.”

But it doesn't matter anyway because at last I have figured out that the USB A host port is connected to the OMAP through a USB3326 PHY, therefore the above is irrelevant. The USB3326 only supports full-speed if accompanied by an external full-speed PHY, which is absent on the Overo (unless I'm really mistaken). I also got confirmation from someone at TI that there is _no_ way to use a FS device on that port without a hub. Major bummer.

Perhaps the least kludgy solution from an end-user perspective would be a splitter cable with data lines from the OTG port (which should support FS) and power to the A port, if that will work at all…

Alexander



On Wed, Jul 27, 2011 at 4:16 PM, Steve Modica <modica@small-tree.com> wrote:
Do you have the omap3 manual?  I think that details the correct backend pin mode.  Steve S sent out a pointer to it on one of the threads. 
I'm definitely interested in this functionality as well. 

On Jul 27, 2011, at 5:13 AM, Alexander Thomas wrote:

OK, I have figured out that I need to:
1. disable EHCI and enable OHCI support in the kernel,
2. remove ehci init code from board-overo.c and add missing ohci init code.

I have to call usb_ohci_init with a ‘ohci_hcd_omap_platform_data’ struct, but I have no idea what value I should use for port_mode[1]. Given that the ehci struct uses EHCI_HCD_OMAP_MODE_PHY, it seems logical that I should use one of these four possible ohci_omap3_port_mode values:

    OMAP_OHCI_PORT_MODE_PHY_6PIN_DATSE0,
    OMAP_OHCI_PORT_MODE_PHY_6PIN_DPDM,
    OMAP_OHCI_PORT_MODE_PHY_3PIN_DATSE0,
    OMAP_OHCI_PORT_MODE_PHY_4PIN_DPDM

Which one is correct for the Overo+Tobi?

Alexander

On Mon, Jul 25, 2011 at 6:29 PM, Victhor <victhor.foster@gmail.com> wrote:
There is a OHCI kernel module for the OMAP3 USB controller, but I never
had the opportunity to test it.
>
> On Jul 25, 2011, at 10:02 AM, Alexander Thomas wrote:
>
> > On Mon, Jul 25, 2011 at 4:43 PM, Steve Modica
> > <modica@small-tree.com> wrote:
> >
> >         On Jul 25, 2011, at 7:30 AM, Alexander Thomas wrote:
> >
> >         > Hi,
> >         > Is there any expansion board for the Overo COMs that has
> >         an Ethernet port and allows to directly attach a full-speed
> >         USB device? We already have a Tobi but it proves to only
> >         support high-speed devices. Unless I'm mistaken the only way
> >         to connect a full-speed device like an USB audio device is
> >         to connect it through a hub, which would complicate our
> >         design considerably if we want to keep it a single unit.
> >
> >
> >         You can put a full speed device on the OTG port.  It's an AB
> >         port so there's nothing hard about that.  Get a miniAB to B
> >         cable and you're all set.
> >
> > Except for the fact that the OTG port only delivers up to 100mA and
> > the audio device requires 400mA.
> >
> > The strange thing is that the OMAP3530's specifications include
> > “High-Speed/Full-Speed/Low-Speed Multiport USB Host Subsystem”. Why
> > does the port on the Tobi only support high-speed? Can it be
> > switched to low/full speed mode? We couldn't care less if that would
> > mean losing high-speed.
> >
>
>
> The Host A port has the ability to support Full Speed devices *but*
> you have to put the chip into OHCI mode and that requires a different
> back end interface (which appears to be missing).  So if you want to
> do this, you have to create that backend interface
>
> >
> > Alexander
> >
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>
>
>
>
>
>
>
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