Chipidea usb otg support for IMX/MXS (device functionality)

[Chen Peter-B29397]

> 
> > > -----Original Message-----
> > > From: Marek Vasut [mailto:marex at denx.de]
> > > Sent: Sunday, July 07, 2013 9:10 AM
> > > To: Chen Peter-B29397
> > > Cc: shawn.guo at linaro.org; Michael Grzeschik; maxime.ripard at free-
> > > electrons.com; Hector Palacios; linux-usb at vger.kernel.org;
> > > s.hauer at pengutronix.de; alexander.shishkin at linux.intel.com; Estevam
> > > Fabio-R49496; Marc Kleine-Budde; m.grzeschik at pengutronix.de; linux-
> arm-
> > > kernel at lists.infradead.org
> > > Subject: Re: Chipidea usb otg support for IMX/MXS (device
> functionality)
> > >
> > > Hi Peter,
> > >
> > > > > Where can I measure this?
> > > > >
> > > > > > Two possible reasons:
> > > > > >
> > > > > > 1. You have not gpio control for vbus toggle when role switches.
> > > > >
> > > > > This works well.
> > > > >
> > > > > > 2. Your hardware has some problems that the vbus can't lower
> than
> > >
> > > 0.8v.
> > >
> > > > > How can I check that?
> > > >
> > > > Just measure the voltage of your otg vbus pin.
> > >
> > > It's 2.5 volt for me. What am I supposed to observe happening there?
> >
> > http://marc.info/?l=linux-usb&m=137242465920952&w=2
> 
> Dang, must have missed that one, sorry.
> 
> The VBUS is slowly discharging from around 5V to 2.5V , what does that
> tell me?
> 

It needs to check your hardware, it is probably there is a high capacitance at
vbus pin. Besides, the vbus should be lower than 0.8v if it is disconnected from
pc.

Best regards,
Peter