Some hardware like the ocelot/felix switch PHC can emit PPS signals but not starting from arbitrary absolute times, but rather phase-aligned to the beginning of a second.
For those, it was established that they should reject any other absolute time for the PTP_PEROUT_REQUEST than 0.000000000 [1]. So currently ts2phc would fail as below: ts2phc -s /dev/ptp1 -f ts2phc.cfg -m [242238.618012] mscc_felix 0000:00:00.5: Absolute start time not supported! [242238.624878] mscc_felix 0000:00:00.5: Accept nsec for PPS phase adjustment, otherwise start time should be 0 0. ts2phc[242238.506]: PTP_PEROUT_REQUEST2 failed: Invalid argument failed to create master Actually there's no good reason why ts2phc would specify an absolute start time of (current time + 2 seconds, 0) for its most basic operation. The (0, 0) start time should be accepted by all drivers, and the behavior should be that some platform-level decision (hardware or driver) is taken such that the requested time is advanced such that it becomes a valid start time in the immediate future (based on the cycle time, which is 1 second). This is similar to how other PTP-based networking APIs work (such as tc-taprio, tc-gate). We can argue that ocelot/felix supports this (and just this). [1]: https://patchwork.ozlabs.org/project/netdev/patch/20200320103726.32559-7-yangbo...@nxp.com/ Quote below: On Tue, 24 Mar 2020 at 15:19, Richard Cochran <richardcoch...@gmail.com> wrote: > > On Tue, Mar 24, 2020 at 05:21:27AM +0000, Y.b. Lu wrote: > > In my one previous patch, I was suggested to implement PPS with > > programmable pin periodic clock function. > > But I didn’t find how should PPS be implemented with periodic clock > > function after checking ptp driver. > > https://patchwork.ozlabs.org/patch/1215464/ > > Yes, for generating a 1-PPS output waveform, users call ioctl > PTP_CLK_REQ_PEROUT with ptp_perout_request.period={1,0}. > > If your device can't control the start time, then it can accept an > unspecified time of ptp_perout_request.start={0,0}. > > > Vladimir talked with me, for the special PPS case, we may consider, > > if (req.perout.period.sec ==1 && req.perout.period.nsec == 0) and > > configure WAVEFORM_LOW to be equal to req_perout.start.nsec. > > > > Richard, do you think is it ok? > > Sound okay to me (but I don't know about WAVEFORM_LOW). Signed-off-by: Vladimir Oltean <olte...@gmail.com> --- ts2phc_phc_master.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/ts2phc_phc_master.c b/ts2phc_phc_master.c index 9f1837bc80eb..82f79820d9bf 100644 --- a/ts2phc_phc_master.c +++ b/ts2phc_phc_master.c @@ -47,7 +47,7 @@ static int ts2phc_phc_master_activate(struct config *cfg, const char *dev, } memset(&perout_request, 0, sizeof(perout_request)); perout_request.index = master->channel; - perout_request.start.sec = ts.tv_sec + 2; + perout_request.start.sec = 0; perout_request.start.nsec = 0; perout_request.period.sec = 1; perout_request.period.nsec = 0; -- 2.25.1 _______________________________________________ Linuxptp-devel mailing list Linuxptp-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-devel
