Re: [Linuxptp-users] can't get linux PTP to run

[Keller, J. E <jac...@in...>]

> -----Original Message-----
> From: Tim...@de... [mailto:Tim-
> Ben...@de...]
> Sent: Monday, April 08, 2013 7:22 AM
> To: ric...@gm...
> Cc: lin...@li...
> Subject: Re: [Linuxptp-users] can't get linux PTP to run
> 
> I'm not on kernel 3.9 maybe that's why I get the 25usec offset.
> My master clock is using hardware time stamping with kernel 3.2 (with
> RT support) and the patched e1000e driver.
> (http://sourceforge.net/projects/e1000/files/e1000e%20stable/)
> 
> What offset do you get and how do you measure it? Maybe I do get the
> error because of my way to measure the offset.
> 
> Benny
> 
> -----Ursprüngliche Nachricht-----
> Von: Richard Cochran [mailto:ric...@gm...]
> Gesendet: Samstag, 6. April 2013 11:58
> An: Rapp, Tim-Benjamin
> Cc: lin...@li...
> Betreff: Re: [Linuxptp-users] can't get linux PTP to run
> 
> On Wed, Apr 03, 2013 at 06:44:30AM +0000, Tim-
> Ben...@de... wrote:
> >
> > Well I'm testing on a custom board. It's the control for a laser machine-
> tool.
> >
> > The Ethernet modules and drivers are: "e1000e version: 2.3.2-NAPI,
> Intel Corporation 82574L Gigabit Network Connection, Intel(R) PRO/1000
> Network Connection"
> > I've tried to turn a little bit at the servo number but to be honest I can't
> really figure out what the different numbers are.
> 
> Today I tried my 82574 card with kernel 3.9-rc2 and the lastest ptp4l, and
> it seems to be working fine. Perhaps the 25 usec offset error you see is
> because your master clock is using software time stamping?
> 
> HTH,
> Richard
> 

We measure offset using what ptp4l displays. More accurate measurement can be done with some hardware setups which actually directly output clock to a pin, etc. But most cards I have cannot do this, and even then ptp4l is pretty accurate. Is ptp4l itself displaying +/-25 on the screen?

Here is example log for my cards -

ptp4l[499579.068]: selected /dev/ptp1 as PTP clock
ptp4l[499579.070]: port 1: INITIALIZING to LISTENING on INITIALIZE
ptp4l[499579.070]: port 0: INITIALIZING to LISTENING on INITIALIZE
ptp4l[499585.070]: port 1: LISTENING to MASTER on ANNOUNCE_RECEIPT_TIMEOUT_EXPIRES
ptp4l[499592.971]: port 1: new foreign master a0369f.fffe.0e2288-1
ptp4l[499596.971]: selected best master clock a0369f.fffe.0e2288
ptp4l[499596.971]: port 1: MASTER to UNCALIBRATED on RS_SLAVE
ptp4l[499597.973]: master offset      64733 s0 freq      +0 path delay      2240
ptp4l[499598.973]: master offset      64733 s1 freq      +0 path delay      2240
ptp4l[499599.973]: master offset      -1632 s2 freq   -1632 path delay      2240
ptp4l[499599.973]: port 1: UNCALIBRATED to SLAVE on MASTER_CLOCK_SELECTED
ptp4l[499600.973]: master offset         64 s2 freq    -426 path delay      2174
ptp4l[499601.973]: master offset        503 s2 freq     +33 path delay      2161
ptp4l[499602.973]: master offset        472 s2 freq    +152 path delay      2161
ptp4l[499603.973]: master offset        285 s2 freq    +107 path delay      2196
ptp4l[499604.973]: master offset        158 s2 freq     +66 path delay      2215
ptp4l[499605.973]: master offset         93 s2 freq     +48 path delay      2215
ptp4l[499606.973]: master offset         44 s2 freq     +27 path delay      2216
ptp4l[499607.974]: master offset         16 s2 freq     +12 path delay      2217
ptp4l[499608.974]: master offset          4 s2 freq      +5 path delay      2217
ptp4l[499609.974]: master offset         -8 s2 freq      -6 path delay      2225
ptp4l[499610.974]: master offset        -21 s2 freq     -21 path delay      2243
ptp4l[499611.974]: master offset          0 s2 freq      -7 path delay      2243
ptp4l[499612.974]: master offset         -4 s2 freq     -11 path delay      2253
ptp4l[499613.974]: master offset         11 s2 freq      +3 path delay      2248
ptp4l[499614.974]: master offset          8 s2 freq      +3 path delay      2247
ptp4l[499615.974]: master offset          5 s2 freq      +3 path delay      2247

Note that the master offset is measured in *nanoseconds* not microseconds. And that offset is as measured by PTP4l, but does not necessarily directly match offset of two pins set to create a clock signal. That is a much more complicated setup. It is also the only way to get more accurate information. If you just "read clock A, read clock B" you have a lot of slop between reads. And even if you "read clock A, read clock B, read clock A" and average the times you are really not accurate either.

- Jake