> On 4 mars 2016, at 19:00, Ian Lepore <i...@freebsd.org> wrote: > >> On Fri, 2016-03-04 at 10:54 -0600, Karl Denninger wrote: >>> On 3/3/2016 12:57, Peter Ankerstål wrote: >>> Hi! >>> >>> I have sort of exactly the same question as Erik: >>> http://lists.freebsd.org/pipermail/freebsd-questions/2014-July/2590 >>> 55.html >>> >>> I have bought a https://learn.adafruit.com/adafruit-ultimate-gps an >>> d want to use the PPS output to discipline my clock. >>> >>> But the only source of information on how PPS works in FreeBSD I >>> could find is this: >>> https://docs.freebsd.org/doc/8.0-RELEASE/usr/share/doc/ntp/pps.html >>> and it clearly states the two ways to provide a PPS signal. "The >>> PPS signal can be connected in either of two ways: via the data >>> carrier detector (DCD) pin of a serial port or via the acknowledge >>> (ACK) pin of a parallel port” >>> >>> Since the Pi doesn´t have any DCD pin i would like to use a generic >>> GPIO for this. There is a linux kernel module for this: http://lxr. >>> free-electrons.com/source/drivers/pps/clients/pps-gpio.c?v=3.6 >> GPIO is supported on the Pi, I'm using it on 11-Current on my home >> control software to drive relays on my pool hardware (e.g. valves, >> heater, VFD motor drive, etc) and it is working very well. I don't >> believe tapping into that at the kernel level to expose a pps signal >> (e.g. on /dev/pps or something of the like) would be very difficult >> at >> all, since the low-level driver capability is already present. >> >> If I get some free time I'll dig around a bit and see if I can cobble >> something up. It's of some interest to me as well since I have a GPS >> clock here that currently talks to a serial port on an Intel-based >> machine and being able to move that to a $35 "appliance" for NTP >> using >> the Adafruit setup looks sort of attractive given that the Pi plus >> the >> module would be under $100 all-in. > > Don't "cobble something up" just yet... there is "a right way" to fix > this, which is a generic gpio-pps driver. The problem is that it > requires support from the new INTRNG, and the rpi hasn't been converted > to that yet. I'm checking around to see if someone has done the > conversion for rpi and it just hasn't been reveiwed/committed yet; if > not, I guess I'll try to do it myself. > > Writing the actual gpio-pps driver will be pretty quick and easy once > we have the intrng support, I think it'll take me a couple hours. > Oh, so there is hope. Thanks for looking into it.
Im not a programmer myself but im willing to help if I can. > Also, FYI, another option with PPS is to use a usb-serial adapter and > feed the PPS in on the CTS or DCD pin. I tested that on rpi a few > months ago and it worked fine. There's surpisingly little jitter even > when the usb bus is heavily loaded with other traffic such as disk or > network IO. > Yes that was going to be my plan B. Good to know that it works. /Peter.
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