6.1.16. Configuring Trimble Palisade/Acutime Refclocks

This topic explains how to get a Trimble Palisade/Acutime refclock working and points out some tips that will be useful for increasing the accuracy of this refclock when using a Linux kernel based OS.

The first thing todo is to read a refclocks drivers description, which can be found at https://www.eecis.udel.edu/~mills/ntp/html/drivers/driver29.html

6.1.16.1. Getting it working:

• Connect Synchronization Kits PortA to your machine
• Link your serial port (usually /dev/ttySX) to /dev/palisadeX. On my laptop there is no serial port, so I used a USB to RS232 converter and, in this case, the device would be /dev/ttyUSBX (the exact device name depends on your system configuration).
• Add the following lines to ntp.conf. Pay attention to time2 value which enables or disables the event polling mechanism (it depends on your SynchKits firmware version). More details about this flag are in the link mentioned above.

       //replace X with the corresponding serial line number
       server 127.127.29.X
       fudge  127.127.29.X stratum 0
       fudge  127.127.29.X refid GPS   //reference ID - name it as you wish
       fudge  127.127.29.X time1 0.020 //this value may vary depending on the latency acquired through a long antenna or synchkit cable

• Start ntp server and check for the state off refclock using ntpq cli. Use these simple cli commands: associations and peers. Here's how it looks on my machine:

       ntpq> associations
       ind assID status  conf reach auth condition  last_event cnt
       -----------------------------------------------------------
       1   11388  9614   yes   yes  none  sys.peer   reachable  1
       ntpq> peers
       remote           refid           st t when poll reach   delay   offset  jitter
       ------------------------------------------------------------------------------
       *GPS_PALISADE(0) .GPS.            0 l   30   32  377    0.000    0.000   0.001

• Keep using ntpd :)

6.1.16.2. Making the clock more accurate

6.1.16.2.1. Min / Max Poll Values

First thing to adjust are the max and min poll values. These values can be added to the refclock driver configuration in your ntp.conf:

       fudge server 127.127.29.x minpoll Y maxpoll Z

       #define TRMB_MINPOLL    4       /* 16 seconds */
       #define TRMB_MAXPOLL    5       /* 32 seconds */

The smallest and largest allowable polling values are 4 (16 seconds) and 17 (1.5 days) respectively.

6.1.16.2.2. APIC support in Linux 2.6.x Kernels

When I searched Google, I found lots of reports that clock is sometimes going crazy when APIC is enabled in the Linux kernel. Try disabling your APIC support.

6.1.16.2.3. ACPI

The next thing I encountered when trying to run ntpd on my laptop was problems caused by ACPI. The first thing to do is to check out known hardware issues and read the mailing list links about that. The simple way to deal with scaling CPU frequency is just to disable the ACPI. I suggest adding this line to your lilo.conf (for grub and other loaders the option may be different):

       append="acpi=off"

6.1.16.2.4. Results

Here are some results describing images with comments what was done to get these results

• The offset results on my workstation without event polling enabled and with APIC
• The offset results on my workstation with event polling and still with APIC

Some results describing pictures, that were retrieved during ntpd configuration on my laptop

• Offset when the system disables APIC in kernel
• Offset without APIC and ACPI support
• Offset without APIC, ACPI and CPU scaling feature and noflushd (for hdd controling) daemon killed

Still no big difference between graphs?

• Here's the final graph without all features that were mentioned above and with event polling enabled (don't miss this one, because you see how different this graph is and that's because of my stupid mistake not to enable it :)

So the achieved accuracy is within the limits described in the refclocks page:

       Platform     Operating System     NTP Sources       Accuracy
       i386 (PC)    Linux                NTP Distribution  10 us

Only on a workstation it's more stable than on my laptop, there are still some hidden features to play with on that.

6.1.16.3. How did I get and graph the data?

I wrote a small C program to get the data:

       #include <sys/timex.h>
       #include <sys/time.h>
       #include <stdio.h>
       int main(){
       int i;               //simple integer for retrieved result count
       struct timex *adjtm; //ntp_adjtime pointer
       adjtm = (struct timex *)malloc(sizeof(struct timex));
       struct timeval ts;
       for (i=0;i<=3600;i++) {
       ntp_adjtime(adjtm);
       printf("%i\t%i\n",i, (unsigned int) adjtm->offset); //print the info (also You can modify to print directly to file)
       sleep(1);               //wait for 1 sec and then retrieve data again (can use even nanosleep-it's up to You)
       } //for
       } //main

Compile and simply run #program > output.file

To draw the graphs I fed the output generated by program above to gnuplot. Here's quick guide of how to do it:

       gnuplot> set terminal png transparent size 1024,400
       gnuplot> set xlabel "time,s"
       gnuplot> set ylabel "offset,us"
       gnuplot> set title "Your title here"
       gnuplot> set output "filename.png"
       gnuplot> plot "output.file",x*0
       gnuplot> quit

-- VaidotasJanuska - 08 Dec 2004

Related Topics: TrimblePalisadeAcutimeRefclockUsers