PTP 时钟

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

PTP-P2P-Capture.pcap

Example:

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/system_administrators_guide/ch-configuring_ptp_using_ptp4l#sec-Using_the_PTP_Management_Client

GET

pmc -u -b 0 'GET PORT_DATA_SET'

pmc -u -b 0 -d 0 'GET TIME_STATUS_NP'

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'

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

LOG

tail -f /var/log/messages | grep ptp4l

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

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

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

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

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

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

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

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

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

The rms value 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 reports rms lower 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

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

If the output shows NTP service: active, disable it:

Disable NTP

timedatectl set-ntp false

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:

Network Configure

[main]

plugins=keyfile

 

[keyfile]

unmanaged-devices=interface-name:eth0

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

https://gstreamer.freedesktop.org/documentation/avtp/index.html?gi-language=c#audio-video-transport-protocol-avtp-plugin

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

• Audio Video Transport Protocol (AVTP) Plugin for PTP 

• 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