BBB uarts & pps dts definitions

[Tony Hain]

Ian Lepore wrote:
 
> On Thu, 2017-01-26 at 15:41 -0800, Tony Hain wrote:
> >
> > >
> > > -----Original Message-----
> > > From: Ian Lepore [mailto:ian at freebsd.org]
> > > Sent: Thursday, January 26, 2017 1:33 PM
> > > To: Tony Hain; freebsd-arm at freebsd.org
> > > Subject: Re: BBB uarts & pps dts definitions
> > >
> > > On Thu, 2017-01-26 at 12:53 -0800, Tony Hain wrote:
> > > >
> > > > Ian Lepore wrote:
> > > >
> > > > >
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> > > > > > > > > > > > snip
> > > > > >
> > > > > > [even more snip]
> > That makes some degree of sense based on what I am seeing, though that
> > is a very low input impedance on the BBB. I was expecting ~100k. My
> > source is a
> > 555 on an ancient ttl/RS232 board I built because the 20 us pulse from
> > the GPS was too fast (between the slew rate of the 3232 and the DCD
> > detection window on the com port) to go with a simple level
> > conversion. Sounds like it might be best to do an active 3.3v driver at
this
> point.
> >
> > Tony
> 
> BTW, not related to the BB stuff... a while back I added "narrow pulse
> capture" support to uart(4) for CTS/DCD PPS capture, you can use it with
> pulses as narrow as 1uS, maybe even less on some hardware.  The tradeoff
is
> that you can only capture assert edges, not clear.  The support goes back
to
> 10.3 or so, details are in the uart(4) manpage.

I saw references to that and was going to go looking for them again if the
timer pin approach failed. I was not overly hopeful though because it was
not clear to me how that would mesh with using NTPsec which would be
expecting a DCD transition. Let's hope the fix in the other note resolves
this so I never have to worry about that.

Tony