[U-Boot] [PATCH v1 0/2] usb: dfu: am335x: allow dfu in fullspeed mode only

[Stockmann, Lukas]

Hi all

> -----Ursprüngliche Nachricht-----
> Von: Heiko Schocher [mailto:hs at denx.de]
> Gesendet: Dienstag, 9. September 2014 16:22
> An: Lukasz Majewski
> Cc: u-boot at lists.denx.de; Tom Rini; Marek Vasut; Liu Bin; Stockmann, Lukas
> Betreff: Re: [PATCH v1 0/2] usb: dfu: am335x: allow dfu in fullspeed mode
> only
> 
> Hello Lukasz,
> 
> Am 09.09.2014 15:43, schrieb Lukasz Majewski:
> > Hi Heiko,
> >
> >> This patchserie adds the new config option CONFIG_DFU_FULLSPEED.
> >
> > Is there any special reason to support Full Speed (12 Mbit/sec - USB
> > 1.1) and not rely solely on the High Speed (USB 2.0) as we do now?
> >
> >> If this is enabled DFU uses fullspeed only. This is used on the
> >> siemens boards.
> >
> > Is there any DFU problem with the mentioned Siemens board, that we
> > must use USB 1.1?
> >
> > I'd also appreciate more verbose rationale for this patch series - why
> > this change is needed? What is the expected improvement?
> 
> They have a "USB HW protection circuit" and therefore they only allowed to
> use fullspeed ...
> 
> @Lukas Stockman: Maybe you could answer this better than me?

Yes, it's because of a protection circuit. Our device is 24V AC
powered, if someone uses a non galvanically isolated transformer and misswires it,
it could burn down the USB host. That's why we have a protection on the USB
side which limits the speed to 12Mbit/sec.

Regards,
Lukas