BBB uarts & pps dts definitions

[Ian Lepore]

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
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> > > > > [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.

-- Ian