Basic
SyncE Principle mechanism
SyncE is only frequency synchronization, while SyncE and PTP are time synchronization together.
PTP Principle mechanism
There are 2 ptp delay-mechanism { e2e | p2p }
By default, different protocol standards correspond to different delay measurement mechanisms.
The defaults of different PTP protocol standards are different:
- When the PTP protocol standard is IEEE 1588 version 2 and SMPTE ST 2059-2, the default delay measurement mechanism is the request-response mechanism.
- When the PTP protocol standard is IEEE 802.1AS, the default delay measurement mechanism is the end delay mechanism
Offset = (t2 – t1) – [(t2 – t1) + (t4 – t3)] / 2 = [(t2 – t1) – (t4 – t3) ] / 2
We can show offset in ptp4l log
Offset is positive(+), indicating that the local clock is faster than the master clock.
Offset is negative(-), indicating that the local clock is slower than the master clock.
Dump PTP package
Example:
GET
pmc -u -b 0 'GET PORT_DATA_SET'
pmc -u -b 0 -d 0 'GET TIME_STATUS_NP'
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All get command
GET
hops=${hops:-0}
dom=${dom:-0}
pmc -u -b $hops -d $dom 'GET ANNOUNCE_RECEIPT_TIMEOUT'
pmc -u -b $hops -d $dom 'GET CLOCK_ACCURACY'
pmc -u -b $hops -d $dom 'GET CLOCK_DESCRIPTION'
pmc -u -b $hops -d $dom 'GET CURRENT_DATA_SET'
pmc -u -b $hops -d $dom 'GET DEFAULT_DATA_SET'
pmc -u -b $hops -d $dom 'GET DELAY_MECHANISM'
pmc -u -b $hops -d $dom 'GET DOMAIN'
pmc -u -b $hops -d $dom 'GET GRANDMASTER_SETTINGS_NP'
pmc -u -b $hops -d $dom 'GET LOG_ANNOUNCE_INTERVAL'
pmc -u -b $hops -d $dom 'GET LOG_MIN_PDELAY_REQ_INTERVAL'
pmc -u -b $hops -d $dom 'GET LOG_SYNC_INTERVAL'
pmc -u -b $hops -d $dom 'GET NULL_MANAGEMENT'
pmc -u -b $hops -d $dom 'GET PARENT_DATA_SET'
pmc -u -b $hops -d $dom 'GET PORT_DATA_SET'
pmc -u -b $hops -d $dom 'GET PORT_DATA_SET_NP'
pmc -u -b $hops -d $dom 'GET PRIORITY1'
pmc -u -b $hops -d $dom 'GET PRIORITY2'
pmc -u -b $hops -d $dom 'GET SLAVE_ONLY'
pmc -u -b $hops -d $dom 'GET TIMESCALE_PROPERTIES'
pmc -u -b $hops -d $dom 'GET TIME_PROPERTIES_DATA_SET'
pmc -u -b $hops -d $dom 'GET TIME_STATUS_NP'
pmc -u -b $hops -d $dom 'GET TRACEABILITY_PROPERTIES'
pmc -u -b $hops -d $dom 'GET USER_DESCRIPTION'
pmc -u -b $hops -d $dom 'GET VERSION_NUMBER'
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When PTP time synchronization is working properly, new messages with offsets and frequency adjustments will be printed periodically to the ptp4l and phc2sys
(if hardware time stamping is used) outputs. These values will eventually converge after a short period of time. These messages can be seen in /var/log/messages file
tail -f /var/log/messages | grep ptp4l
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check sys clock
SYS CLOCK
cat /sys/devices/system/clocksource/clocksource0/available_clocksource
cat /sys/devices/system/clocksource/clocksource0/current_clocksource
# echo 'tsc' > /sys/devices/system/clocksource/clocksource0/current_clocksource
cat /proc/timer_list
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check PTP clock name
PTP Clock Name
# cat /sys/class/ptp/ptp*/clock_name
tg3 clock
i40e
ice-0000:31:00
tg3 clock
i40e
i40e
i40e
i40e
i40e
# cat /sys/class/ptp/ptp10/clock_name
i40e
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1588 Profile Configuration Validation
More details ref 4.71588 Profile Configuration Validation Tool for ptp4l
There are several configuration file for the G.8265.1, G.8275.1, or G.8275.2 profiles, ref: https://www2.renesas.cn/us/en/document/whp/linux-phc-infrastructure-5g
PTP profiles
# ps -ef |grep ptp
root 105083 1 0 Jan14 ? 00:00:09 tmux new-session -s ptp1588 -n PTP -d
root 105161 105092 0 Jan14 pts/3 00:00:15 ptp4l -i p1p4 -m -f /root/default_slave.cfg
# cat /root/default_slave.cfg
[global]
dataset_comparison G.8275.x
G.8275.defaultDS.localPriority 255
logAnnounceInterval 3
masterOnly 0
G.8275.portDS.localPriority 255
hybrid_e2e 1
inhibit_multicast_service 1
unicast_listen 1
unicast_req_duration 32
#
# Customize the following for slave operation:
#
[unicast_master_table]
table_id 1
logQueryInterval 3
UDPv4 192.168.1.149
#
[p1p4]
unicast_master_table 1
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PI servo
The proportional integral servo system is integrated for ptp4l, which can resist interference. Parameters need to be adjusted:
Precision Time Protocol on Linux ~ Introduction to linuxptp
PI servo for Linux ptp4l
Synchronizing the System Clock
check phc clock bigger than 1000
PHC offset
LEN=4 # 4 means 1000， 3 means 100
grep -E "phc offset\s+[0-9]{$LEN,}" /var/log/messages
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check phc clock rms than 100
PHC RMS
LEN=3 # 4 means 1000， 3 means 100
grep -E "phc2sys.*rms\s+[0-9]{$LEN,}" /var/log/messages
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hc2sys reports the time offset between PHC and System Clock, which determines if the clocks are synchronized.
phc2sys[5374168.545]: CLOCK_REALTIME phc offset -372582 s0 freq +246 delay 6649 phc2sys[5374169.545]: CLOCK_REALTIME phc offset -372832 s1 freq -4 delay 6673 phc2sys[5374170.547]: CLOCK_REALTIME phc offset 68 s2 freq +64 delay 6640 phc2sys[5374171.547]: CLOCK_REALTIME phc offset -20 s2 freq -3 delay 6687 phc2sys[5374172.547]: CLOCK_REALTIME phc offset 47 s2 freq +58 delay 6619 phc2sys[5374173.548]: CLOCK_REALTIME phc offset -40 s2 freq -15 delay 6680
The offset information reported by phc2sys shows the time offset between the PHC and the System clock. If phc2sys consistently reports offset lower than 100 ns, the System clock is synchronized.
check phc clock max than 100
PHC MAX
LEN=4 # 3 means 1000， 3 means 100
grep -E "phc2sys.*max\s+[0-9]{$LEN,}" /var/log/messages
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check ptp clock bigger than 1000
PTP OFFSET
LEN=4 # 4 means 1000， 3 means 100
grep -E "master offset\s+[0-9]{$LEN,}" /var/log/messages
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check ptp clock max bigger than 100
PTP RMS
LEN=3 # 4 means 1000， 3 means 100
grep -E "ptp4l.*rms\s+[0-9]{$LEN,}" /var/log/messages
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The output for ptp4l is:
ptp4l[5374018.735]: rms 787 max 1208 freq -38601 +/- 1071 delay -14 +/- 0 ptp4l[5374019.735]: rms 1314 max 1380 freq -36204 +/- 346 delay -14 +/- 0 ptp4l[5374020.735]: rms 836 max 1106 freq -35734 +/- 31 delay -14 +/- 0 ptp4l[5374021.736]: rms 273 max 450 freq -35984 +/- 97 delay -14 +/- 0 ptp4l[5374022.736]: rms 50 max 82 freq -36271 +/- 64 delay -14 +/- 0 ptp4l[5374023.736]: rms 81 max 86 freq -36413 +/- 17 delay -14 +/- 0
Thermsvalue reported by ptp4l once the slave has locked with the GM shows the root mean square of the time offset between the PHC and the GM clock.
If ptp4l consistently reportsrmslower than 100 ns, the PHC is synchronized
check ptp clock rms bigger than 100
PTP MAX
LEN=3 # 4 means 1000， 3 means 100
grep -E "ptp4l.*max\s+[0-9]{$LEN,}" /var/log/messages
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What is with al of these TLVs in the Precision Time Protocol?
Let’s start at the beginning, TLV stands for “type, length, value.” It is a general means to extend a PTP message with some extra information for some optional feature or whatever. TLVs are used in many network protocols, not just PTP. A TLV in PTP has the structure:
Troubleshooting
REF：https://tsn.readthedocs.io/timesync.html#troubleshooting
In this section we discuss some issues that we have faced when trying to synchronize time using Linux PTP in different systems
System time isn’t synchronized with PHC
If PHC offset never goes below hundreds (of nanoseconds)- or if it suddenly spikes (as seen on phc2sys log) - leaving system time out of sync, this section provides some hints on what to do.
Confirm NTP is not running
An NTP service may be running and changing the system clock. On systems with systemd, run:
Check NTP
timedatectl | grep NTP
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If the output shows NTP service: active, disable it:
Disable NTP
timedatectl set-ntp false
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Check if NTP has been disabled and run the clock synchronization steps again and verify that the clocks are in sync.
Check NetworkManager is not messing with the NIC
When NetworkManager is running, it may reset the NIC after the qdisc setup. In this situation, PHC and the system clock may be out of sync. Do not allow the NetworkManager to manage the TSN capable NIC. Add the following to the /etc/NetworkManager/NetworkManager.conf file:
[main]
plugins=keyfile
[keyfile]
unmanaged-devices=interface-name:eth0
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Restart NetworkManager. Run the clock synchronization steps again and verify the clocks are in sync.
Ensure qdisc setup is done before clock synchronization
Qdisc setup resets the NIC, and that can make ptp4l out of sync. If any qdisc setup needs to be done after clocks are already in sync, repeat clock synchronization steps again and verify that the clocks are still in sync.
Confirm only one instance of ptp4l or phc2sys is running
Multiple instances of ptp4l or phc2sys adjusting a single clocksource or sending out Sync messages can put the clocks out of sync. So, ensure only a single instance (per network interface) of both the daemons is running at a time. pgrep can be useful to ensure only one instance of a particular process is running. Look at pgrep(1) manpage for more details.
UTC offset change when loosing grand master
phc2sys: don't synchronize clock to itself.
avtp
Audio Video Transport Protocol (AVTP) Plugin
The AVTP plugin implements typical Talker and Listener functionalities that can be leveraged by GStreamer-based applications in order to implement TSN audio/video applications.
REF:
- Using the PTP Management Client Red Hat Enterprise
- documentation.suse.com: Tuning PTP
- pmc(8): PTP management client - Linux man page
- pmc - PTP management client - Ubuntu Manpage Repository
- linuxptp/pmc.8 at master - GitHub
- Configuring the PTP Service
- PMC Example in Smart Edge
- CN: 同步以太网(SyncE)技术白皮书-6W100
- CN: 网络管理和监控配置指导-PTP配置
- CN：网络管理和监控配置指导-时钟同步配置
- CN: ptp 相关
- renesas.cn: Linux PTP Using PHC Adjust Phase Quick Start Manual
- renesas.cn: Linux PHC Infrastructure 5G
- Precision Time Protocol on Linux ~ Introduction to linuxptp
- PI servo for Linux ptp4l
- redhat.com documentation：PTP Improving_Accuracy
- Synchronizing the Linux System Time to a PTP Hardware Clock.pdf
-
Link Layer Discovery Protocol for TLVs
Source code and discussion in Mail list
- 802.1AS Time-Aware Bridge https://sourceforge.net/p/linuxptp/mailman/linuxptp-devel/?viewmonth=201703
- UTC offset change when loosing grand master https://sourceforge.net/p/linuxptp/mailman/linuxptp-users/thread/20170628093158.nm5nirjpbir6qmnd%40localhost.localdomain/
- [Linuxptp-devel] [PATCH RFC v2 00/19] Improved slave servo and grand master support