The 06/21/2018 07:34, Richard Cochran wrote: > On Thu, Jun 21, 2018 at 02:36:02PM +0200, Miroslav Lichvar wrote: > > On Thu, Jun 21, 2018 at 12:24:15AM -0700, Rob Cornall wrote: > > > I know for a different nic like the i210, it has some specific SDPs that > > > can be used > > > for the PPS input - and this could be used to discipline the phc in the > > > nic directly. > > IIRC the imx also has input pins. > > > A bigger problem might be with the PPS timestamping. I'm not sure how > > exactly it works with the imx. If the kernel is timestamping > > interrupts triggered by the PPS, that will probably add an error of at > > least few microseconds, maybe even few tens of microseconds. Unless > > you can measure the delay and make sure it's stable, 1us accuracy is > > not realistic. > > Right. The delay from interrupt to interrupt handler can be even > hundreds of usec, at it will have jitter. > > > The PPS needs to be timestamped by the HW (like with the i210), or by > > the kernel polling the GPIO pin (assuming the reading is fast enough). > > Right. > > Thanks, > Richard
Well the results are exactly as you say from my testing, we are seeing a pretty constant offset of +25usecs when measuring PPS output on master FEC vs GPS PPS output. (we are running phc2sys -a -r -r to sync System clock to phc on master) I guess for 1us accuracy we will have to connect the GPS PPS directly to the imx6 FEC instead of a GPIO - Another question about connecting the PPS, It does look like there are input pins on imx6 FEC, Do I only need to connect the 1PPS to said pin? My thinking is this: - Initially discipline the PHC with phc2sys using the system clock time (which is set from the GPS NMEA serial stream) - Since this initial time will be within 1 second accuracy, we can use the PPS from here to adjust the PHC. Also it doesn't look like the imx6 fec_ptp driver supports input PPS for Grand master support, do you if any work is happening for this? Appreciate the help. -- Thanks, Rob ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Linuxptp-users mailing list Linuxptp-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-users
