Ubuntu Manpage: ptp4l - PTP Boundary/Ordinary/Transparent Clock

NAME

       ptp4l - PTP Boundary/Ordinary/Transparent Clock

SYNOPSIS

       ptp4l  [  -AEP246HSLmqsv  ]  [  -f config ] [ -p phc-device ] [ -l print-level ] [ -i interface ] [ long-
       options ] ...

DESCRIPTION

       ptp4l is an implementation of the Precision Time Protocol (PTP)  according  to  IEEE  standard  1588  for
       Linux. It implements Boundary Clock (BC), Ordinary Clock (OC), and Transparent Clock (TC).

OPTIONS

-A Select the delay mechanism automatically. Start with E2E and switch to P2P when a peer delay
request is received.

-E Select the delay request-response (E2E) mechanism. This is the default mechanism. All clocks on
single PTP communication path must use the same mechanism. A warning will be printed when a peer
delay request is received on port using the E2E mechanism.

-P Select the peer delay (P2P) mechanism. A warning will be printed when a delay request is received
on port using the P2P mechanism.

-2 Select the IEEE 802.3 network transport.

-4 Select the UDP IPv4 network transport. This is the default transport.

-6 Select the UDP IPv6 network transport.

-H Select the hardware time stamping. All ports specified by the -i option and in the configuration
file must be attached to the same PTP hardware clock (PHC). This is the default time stamping.

-S Select the software time stamping.

-L Select the legacy hardware time stamping.

-f config
Read configuration from the specified file. No configuration file is read by default.

-i interface
Specify a PTP port, it may be used multiple times. At least one port must be specified by this
option or in the configuration file.

-p phc-device
(This option is deprecated.) Before Linux kernel v3.5 there was no way to discover the PHC device
associated with a network interface. This option specifies the PHC device (e.g. /dev/ptp0) to be
used when running on legacy kernels.

-s Enable the slaveOnly mode.

-l print-level
Set the maximum syslog level of messages which should be printed or sent to the system logger. The
default is 6 (LOG_INFO).

-m Print messages to the standard output.

-q Don't send messages to the system logger.

-v Prints the software version and exits.

-h Display a help message.

LONG OPTIONS

       Each and every configuration file option (see below) may also appear  as  a  "long"  style  command  line
       argument.  For example, the slaveOnly option may be set using either of these two forms.

              --slaveOnly 1   --slaveOnly=1

       Option values given on the command line override values in the global section of the configuration file.

CONFIGURATION FILE

       The  configuration  file  is  divided  into sections. Each section starts with a line containing its name
       enclosed in brackets and it follows with settings.  Each  setting  is  placed  on  a  separate  line,  it
       contains  the  name of the option and the value separated by whitespace characters. Empty lines and lines
       starting with # are ignored.

       There are three different section types.

       1.     The global section (indicated as [global]) sets the program options,  clock  options  and  default
              port  options.  Other  sections  are  port  specific  sections  and they override the default port
              options.

       2.     Port sections give the name of the  configured  port  (e.g.   [eth0]).   Ports  specified  in  the
              configuration  file don't need to be specified by the -i option. An empty port section can be used
              to replace the command line option.

       3.     Tables for configuring unicast discovery begin with [unicast_master_table].

              See UNICAST DISCOVERY OPTIONS, below.

PORT OPTIONS

delayAsymmetry
The time difference in nanoseconds of the transmit and receive paths. This value should be
positive when the master-to-slave propagation time is longer and negative when the slave-to-master
time is longer. The default is 0 nanoseconds.

logAnnounceInterval
The mean time interval between Announce messages. A shorter interval makes ptp4l react faster to
the changes in the master-slave hierarchy. The interval should be the same in the whole domain.
It's specified as a power of two in seconds. The default is 1 (2 seconds).

logSyncInterval
The mean time interval between Sync messages. A shorter interval may improve accuracy of the local
clock. It's specified as a power of two in seconds. The default is 0 (1 second).

operLogSyncInterval
The Sync message interval to be requested once the clock enters the SERVO_LOCKED_STABLE state. If
the 'msg_interval_request' option is set, then the local slave port will request the remote master
to switch to the given message rate via a signaling message containing a Message interval request
TLV. This option is specified as a power of two in seconds, and default value is 0 (1 second).

logMinDelayReqInterval
The minimum permitted mean time interval between Delay_Req messages. A shorter interval makes
ptp4l react faster to the changes in the path delay. It's specified as a power of two in seconds.
The default is 0 (1 second).

logMinPdelayReqInterval
The minimum permitted mean time interval between Pdelay_Req messages. It's specified as a power of
two in seconds. The default is 0 (1 second).

operLogPdelayReqInterval
The Pdelay Request messages interval to be used once the clock enters the SERVO_LOCKED_STABLE
state. If the 'msg_interval_request' option is set, then the local slave port will adopt this
rate when the local clock enters the "locked stable" state. This option is specified as a power
of two in seconds, and the default value is 0 (1 second).

inhibit_delay_req
Don't send any delay requests. This will need the asCapable config option to be set to 'true'.
This is useful when running as a designated master who does not need to calculate offset from
slave. The default is 0 (disabled).

announceReceiptTimeout
The number of missed Announce messages before the last Announce messages expires. The default is
3.

syncReceiptTimeout
The number of sync/follow up messages that may go missing before triggering a Best Master Clock
election. This option is used for running in gPTP mode according to the 802.1AS-2011 standard.
Setting this option to zero will disable the sync message timeout. The default is 0 or disabled.

transportSpecific
The transport specific field. Must be in the range 0 to 255. The default is 0.

ignore_transport_specific
By default, incoming messages are dropped if their transportSpecific field does not match the
configured value. However, many of transports specified in the 1588 standard mandate ignoring
this field. Moreover, some equipment is known to set the reserved bits. Configuring this option
as 1 causes this field to be ignored completely on receive. The default is 0.

path_trace_enabled
Enable the mechanism used to trace the route of the Announce messages. The default is 0
(disabled).

follow_up_info
Include the 802.1AS data in the Follow_Up messages if enabled. The default is 0 (disabled).

fault_reset_interval
The time in seconds between the detection of a port's fault and the fault being reset. This value
is expressed as a power of two. Setting this value to -128 or to the special key word "ASAP" will
let the fault be reset immediately. The default is 4 (16 seconds).

fault_badpeernet_interval
The time in seconds between the detection of a peer network misconfiguration and the fault being
reset. The port is disabled for the duration of the interval. The value is in seconds and the
special key word ASAP will let the fault be reset immediately. The default is 16 seconds.

delay_mechanism
Select the delay mechanism. Possible values are E2E, P2P and Auto. The default is E2E.

hybrid_e2e
Enables the "hybrid" delay mechanism from the draft Enterprise Profile. When enabled, ports in the
slave state send their delay request messages to the unicast address taken from the master's
announce message. Ports in the master state will reply to unicast delay requests using unicast
delay responses. This option has no effect if the delay_mechanism is set to P2P. The default is 0
(disabled).

inhibit_multicast_service
Some unicast mode profiles insist that no multicast message are ever transmitted. Setting this
option inhibits multicast transmission. The default is 0 (mutlicast enabled).

net_sync_monitor
Enables the NetSync Monitor (NSM) protocol. The NSM protocol allows a station to measure how well
another node is synchronized. The monitor sends a unicast delay request to the node, which replies
unconditionally with unicast delay response, sync, and follow up messages. If the monitor is
synchronized to the GM, it can use the time stamps in the message to estimate the node's offset.
This option requires that the 'hybrid_e2e' option be enabled as well. The default is 0
(disabled).

unicast_listen
When enabled, this option allows the port to grant unicast message contracts. Incoming requests
for will be granted limited only by the amount of memory available. The default is 0 (disabled).

unicast_master_table
When set to a positive integer, this option specifies the table id to be used for unicast
discovery. Each table lives in its own section and has a unique, positive numerical ID. Entries
in the table are a pair of transport type and protocol address. The default is 0 (unicast
discovery disabled).

unicast_req_duration
The service time in seconds to be requested during unicast discovery. Note that the remote node
is free to grant a different duration. The default is 3600 seconds or one hour.

ptp_dst_mac
The MAC address to which PTP messages should be sent. Relevant only with L2 transport. The
default is 01:1B:19:00:00:00.

p2p_dst_mac
The MAC address to which peer delay messages should be sent. Relevant only with L2 transport. The
default is 01:80:C2:00:00:0E.

network_transport
Select the network transport. Possible values are UDPv4, UDPv6 and L2. The default is UDPv4.

neighborPropDelayThresh
Upper limit for peer delay in nanoseconds. If the estimated peer delay is greater than this value
the port is marked as not 802.1AS capable.

masterOnly
Setting this option to one (1) prevents the port from entering the SLAVE state. In addition, the
local clock will ignore Announce messages received on this port. This option's intended use is to
support the Telecom Profiles according to ITU-T G.8265.1, G.8275.1, and G.8275.2. The default
value is zero or false.

G.8275.portDS.localPriority
The Telecom Profiles (ITU-T G.8275.1 and G.8275.2) specify an alternate Best Master Clock
Algorithm (BMCA) with a unique data set comparison algorithm. The value of this option is
associated with Announce messages arriving on a particular port and is used as a tie breaker
whenever clockClass, clockAccuracy, offsetScaledLogVariance, and priority2 are equal. This option
is only used when "dataset_comparison" is set to "telecom". The default value is 128.

Warning: the BMCA is guaranteed to produce a spanning tree (that is, a timing network without
loops) only when using the default values of G.8275.defaultDS.localPriority and
G.8275.portDS.localPriority. Careful network engineering is needed when using non-default values.

min_neighbor_prop_delay
Lower limit for peer delay in nanoseconds. If the estimated peer delay is smaller than this value
the port is marked as not 802.1AS capable.

tsproc_mode
Select the time stamp processing mode used to calculate offset and delay. Possible values are
filter, raw, filter_weight, raw_weight. Raw modes perform well when the rate of sync messages
(logSyncInterval) is similar to the rate of delay messages (logMinDelayReqInterval or
logMinPdelayReqInterval). Weighting is useful with larger network jitters (e.g. software time
stamping). The default is filter.

delay_filter
Select the algorithm used to filter the measured delay and peer delay. Possible values are
moving_average and moving_median. The default is moving_median.

delay_filter_length
The length of the delay filter in samples. The default is 10.

egressLatency
Specifies the difference in nanoseconds between the actual transmission time at the reference
plane and the reported transmit time stamp. This value will be added to egress time stamps
obtained from the hardware. The default is 0.

ingressLatency
Specifies the difference in nanoseconds between the reported receive time stamp and the actual
reception time at reference plane. This value will be subtracted from ingress time stamps obtained
from the hardware. The default is 0.

boundary_clock_jbod
When running as a boundary clock (that is, when more than one network interface is configured),
ptp4l performs a sanity check to make sure that all of the ports share the same hardware clock
device. This option allows ptp4l to work as a boundary clock using "just a bunch of devices" that
are not synchronized to each other. For this mode, the collection of clocks must be synchronized
by an external program, for example phc2sys(8) in "automatic" mode. The default is 0 (disabled).

udp_ttl
Specifies the Time to live (TTL) value for IPv4 multicast messages and the hop limit for IPv6
multicast messages. This option is only relevant with the IPv4 and IPv6 UDP transports. The
default is 1 to restrict the messages sent by ptp4l to the same subnet.

PROGRAM AND CLOCK OPTIONS

twoStepFlag
Enable two-step mode for sync messages. One-step mode can be used only with hardware time
stamping. The default is 1 (enabled).

slaveOnly
The local clock is a slave-only clock if enabled. The default is 0 (disabled).

socket_priority
Configure the SO_PRIORITY of sockets. This is to support cases where a user wants to route ptp4l
traffic using Linux qdiscs for the purpose of traffic shaping. This option is only available with
the IEEE 802.3 transport (the -2 option) and is silently ignored when using the UDP IPv4/6 network
transports. Must be in the range of 0 to 15, inclusive. The default is 0.

gmCapable
If this option is enabled, then the local clock is able to become grand master. This is only for
use with 802.1AS clocks and has no effect on 1588 clocks. The default is 1 (enabled).

priority1
The priority1 attribute of the local clock. It is used in the best master selection algorithm,
lower values take precedence. Must be in the range 0 to 255. The default is 128.

priority2
The priority2 attribute of the local clock. It is used in the best master selection algorithm,
lower values take precedence. Must be in the range 0 to 255. The default is 128.

clockClass
The clockClass attribute of the local clock. It denotes the traceability of the time distributed
by the grandmaster clock. The default is 248.

clockAccuracy
The clockAccuracy attribute of the local clock. It is used in the best master selection algorithm.
The default is 0xFE.

clockIdentity
The clockIdentity attribute of the local clock. The clockIdentity is an 8-octet array and should
in this configuration be written in textual form, see default. It should be unique since it is
used to identify the specific clock. If default is used or if not set at all, the clockIdentity
will be automtically generated. The default is "000000.0000.000000"

offsetScaledLogVariance
The offsetScaledLogVariance attribute of the local clock. It characterizes the stability of the
clock. The default is 0xFFFF.

G.8275.defaultDS.localPriority
The Telecom Profiles (ITU-T G.8275.1 and G.8275.2) specify an alternate Best Master Clock
Algorithm (BMCA) with a unique data set comparison algorithm. The value of this option is
associated with the local clock and is used as a tie breaker whenever clockClass, clockAccuracy,
offsetScaledLogVariance, and priority2 are equal. This option is only used when
"dataset_comparison" is set to "telecom". The default value is 128.

maxStepsRemoved
When using this option, if the value of stepsRemoved of an Announce message is greater than or
equal to the value of maxStepsRemoved the Announce message is not considered in the operation of
the BMCA. The default value is 255.

domainNumber
The domain attribute of the local clock. The default is 0.

utc_offset
The current offset between TAI and UTC. The default is 37.

free_running
Don't adjust the local clock if enabled. The default is 0 (disabled).

freq_est_interval
The time interval over which is estimated the ratio of the local and peer clock frequencies. It is
specified as a power of two in seconds. The default is 1 (2 seconds).

assume_two_step
Treat one-step responses as two-step if enabled. It is used to work around buggy 802.1AS switches.
The default is 0 (disabled).

tc_spanning_tree
When running as a Transparent Clock, increment the "stepsRemoved" field of Announce messages that
pass through the switch. Enabling this option ensures that PTP message loops never form, provided
the switches all implement this option together with the BMCA.

tx_timestamp_timeout
The number of milliseconds to poll waiting for the tx time stamp from the kernel when a message
has recently been sent. The default is 1.

check_fup_sync
Because of packet reordering that can occur in the network, in the hardware, or in the networking
stack, a follow up message can appear to arrive in the application before the matching sync
message. As this is a normal occurrence, and the sequenceID message field ensures proper matching,
the ptp4l program accepts out of order packets. This option adds an additional check using the
software time stamps from the networking stack to verify that the sync message did arrive first.
This option is only useful if you do not trust the sequence IDs generated by the master. The
default is 0 (disabled).

clock_servo
The servo which is used to synchronize the local clock. Valid values are "pi" for a PI controller,
"linreg" for an adaptive controller using linear regression, "ntpshm" for the NTP SHM reference
clock to allow another process to synchronize the local clock (the SHM segment number is set to
the domain number), and "nullf" for a servo that always dials frequency offset zero (for use in
SyncE nodes). The default is "pi."

clock_type
Specifies the kind of PTP clock. Valid values are "OC" for ordinary clock, "BC" for boundary
clock, "P2P_TC" for peer to peer transparent clock, and "E2E_TC" for end to end transparent clock.
An multi-port ordinary clock will automatically be configured as a boundary clock. The default is
"OC".

pi_proportional_const
The proportional constant of the PI controller. When set to 0.0, the proportional constant will be
set by the following formula from the current sync interval. The default is 0.0.

kp = min(kp_scale * sync^kp_exponent, kp_norm_max / sync)

pi_integral_const
The integral constant of the PI controller. When set to 0.0, the integral constant will be set by
the following formula from the current sync interval. The default is 0.0.

ki = min(ki_scale * sync^ki_exponent, ki_norm_max / sync)

pi_proportional_scale
The kp_scale constant in the formula used to set the proportional constant of the PI controller
from the sync interval. When set to 0.0, the value will be selected from 0.7 and 0.1 for the
hardware and software time stamping respectively. The default is 0.0.

pi_proportional_exponent
The kp_exponent constant in the formula used to set the proportional constant of the PI controller
from the sync interval. The default is -0.3.

pi_proportional_norm_max
The kp_norm_max constant in the formula used to set the proportional constant of the PI controller
from the sync interval. The default is 0.7

pi_integral_scale
The ki_scale constant in the formula used to set the integral constant of the PI controller from
the sync interval. When set to 0.0, the value will be selected from 0.3 and 0.001 for the hardware
and software time stamping respectively. The default is 0.0.

pi_integral_exponent
The ki_exponent constant in the formula used to set the integral constant of the PI controller
from the sync interval. The default is 0.4.

pi_integral_norm_max
The ki_norm_max constant in the formula used to set the integral constant of the PI controller
from the sync interval. The default is 0.3.

step_threshold
The maximum offset the servo will correct by changing the clock frequency instead of stepping the
clock. When set to 0.0, the servo will never step the clock except on start. It's specified in
seconds. The default is 0.0. This option used to be called pi_offset_const.

first_step_threshold
The maximum offset the servo will correct by changing the clock frequency instead of stepping the
clock. This is only applied on the first update. It's specified in seconds. When set to 0.0, the
servo won't step the clock on start. The default is 0.00002 (20 microseconds). This option used
to be called pi_f_offset_const.

max_frequency
The maximum allowed frequency adjustment of the clock in parts per billion (ppb). This is an
additional limit to the maximum allowed by the hardware. When set to 0, the hardware limit will be
used. The default is 900000000 (90%). This option used to be called pi_max_frequency.

sanity_freq_limit
The maximum allowed frequency offset between uncorrected clock and the system monotonic clock in
parts per billion (ppb). This is used as a sanity check of the synchronized clock. When a larger
offset is measured, a warning message will be printed and the servo will be reset. When set to 0,
the sanity check is disabled. The default is 200000000 (20%).

initial_delay
The initial path delay of the clock in nanoseconds used for synchronization of the clock before
the delay is measured using the E2E or P2P delay mechanism. If set to 0, the clock will not be
updated until the delay is measured. The default is 0.

ntpshm_segment
The number of the SHM segment used by ntpshm servo. The default is 0.

udp6_scope
Specifies the desired scope for the IPv6 multicast messages. This will be used as the second byte
of the primary address. This option is only relevant with IPv6 transport. See RFC 4291. The
default is 0x0E for the global scope.

uds_address
Specifies the address of the UNIX domain socket for receiving local management messages. The
default is /var/run/ptp4l.

dscp_event
Defines the Differentiated Services Codepoint (DSCP) to be used for PTP event messages. Must be a
value between 0 and 63. There are several media streaming standards out there that require
specific values for this option. For example 46 (EF PHB) in AES67 or 48 (CS6 PHB) in RAVENNA. The
default is 0.

dscp_general
Defines the Differentiated Services Codepoint (DSCP) to be used for PTP general messages. Must be
a value between 0 and 63. There are several media streaming standards out there that recommend
specific values for this option. For example 34 (AF41 PHB) in AES67 or 46 (EF PHB) in RAVENNA.
The default is 0.

dataset_comparison
Specifies the method to be used when comparing data sets during the Best Master Clock Algorithm.
The possible values are "ieee1588" and "G.8275.x". The default is "ieee1588".

logging_level
The maximum logging level of messages which should be printed. The default is 6 (LOG_INFO).

message_tag
The tag which is added to all messages printed to the standard output or system log. The default
is an empty string (which cannot be set in the configuration file as the option requires an
argument).

verbose
Print messages to the standard output if enabled. The default is 0 (disabled).

use_syslog
Print messages to the system log if enabled. The default is 1 (enabled).

summary_interval
The time interval in which are printed summary statistics of the clock. It is specified as a power
of two in seconds. The statistics include offset root mean square (RMS), maximum absolute offset,
frequency offset mean and standard deviation, and path delay mean and standard deviation. The
units are nanoseconds and parts per billion (ppb). If there is only one clock update in the
interval, the sample will be printed instead of the statistics. The messages are printed at the
LOG_INFO level. The default is 0 (1 second).

time_stamping
The time stamping method. The allowed values are hardware, software and legacy. The default is
hardware.

productDescription
The product description string. Allowed values must be of the form
manufacturerName;modelNumber;instanceIdentifier and contain at most 64 utf8 symbols. The default
is ";;".

revisionData
The revision description string which contains the revisions for node hardware (HW), firmware
(FW), and software (SW). Allowed values are of the form HW;FW;SW and contain at most 32 utf8
symbols. The default is an ";;".

userDescription
The user description string. Allowed values are of the form name;location and contain at most 128
utf8 symbols. The default is an empty string.

manufacturerIdentity
The manufacturer id which should be an OUI owned by the manufacturer. The default is 00:00:00.

kernel_leap
When a leap second is announced, let the kernel apply it by stepping the clock instead of
correcting the one-second offset with servo, which would correct the one-second offset slowly by
changing the clock frequency (unless the step_threshold option is set to correct such offset by
stepping). Relevant only with software time stamping. The default is 1 (enabled).

timeSource
The time source is a single byte code that gives an idea of the kind of local clock in use. The
value is purely informational, having no effect on the outcome of the Best Master Clock algorithm,
and is advertised when the clock becomes grand master.

hwts_filter
Select the hardware time stamp filter setting mode. Possible values are normal, check, full.
Normal mode set the filters as needed. Check mode only check but do not set. Full mode set the
receive filter to mark all packets with hardware time stamp,
so all applications can get them. The default is normal.

asCapable
If set to 'true', all the checks which can unset asCapable variable (as described in Section
10.2.4.1 of 802.1AS) are skipped. If set to 'auto', asCapable is initialized to 'false' and will
be set to 'true' after the relevant checks have passed. The default value is 'auto'.

BMCA This option enables use of static roles for master and slave devices instead of running the best
master clock algorithm (BMCA) described in 1588 profile. This is useful when you know the roles of
the devices in advance. When set to ´noop', the traditional BMCA algorithm used by 1588 is
skipped. masterOnly and slaveOnly will be used to determine master or slave role for the device.
In a bridge, slaveOnly (which is a global option) can be set to make all ports assume the slave
role. masterOnly (which is a per-port config option) can then be used to set individual ports to
take master role. BMCA is used in the Automotive profile to speed up the start time for grand
master and slaves. The default value is 'ptp' which runs the BMCA related state machines.

inhibit_announce
This will disable the timer for announce messages (i.e. FD_MANNO_TIMER) and also the announce
message timeout timer (i.e. FD_ANNOUNCE_TIMER). This is used by the Automotive profile as part of
switching over to a static BMCA. if this option is enabled, ignore_source_id has to be enabled in
the slave because it has no way to identify master identity in Sync and Follow_Up messages. The
default is 0 (disabled).

ignore_source_id
This will disable source port identity checking for Sync and Follow_Up messages. This is useful
when the announce messages are disabled in the master and the slave does not have any way to know
it's identity. The default is 0 (disabled).

msg_interval_request
This option, when set, will trigger an adjustment to the Sync and peer delay request message
intervals when the clock servo transitions into the SERVO_LOCKED_STABLE state. The Sync interval
will be adjusted via the signaling mechanism while the pdelay request interval is simply adjusted
locally. The values to use for the new Sync and peer delay request intervals are specified by the
operLogSyncInterval and operLogPdelayReqInterval options, respectively. The default value of
msg_interval_request is 0 (disabled).

servo_num_offset_values
The number of offset values considered in order to transition from the SERVO_LOCKED to the
SERVO_LOCKED_STABLE state. The transition occurs once the last 'servo_num_offset_values' offsets
are all below the 'servo_offset_threshold' value. The default value is 10.

servo_offset_threshold
The offset threshold used in order to transition from the SERVO_LOCKED to the SERVO_LOCKED_STABLE
state. The transition occurs once the last The default value of offset_threshold is 0 (disabled).

slave_event_monitor
Specifies the address of a UNIX domain socket for slave event monitoring. A local client bound to
this address will receive SLAVE_RX_SYNC_TIMING_DATA and SLAVE_DELAY_TIMING_DATA_NP TLVs. The
default is the empty string (disabled).

write_phase_mode
This option enables using the "write phase" feature of a PTP Hardware Clock. If supported by the
device, this mode uses the hardware's built in phase offset control instead of frequency offset
control. The default value is 0 (disabled).

UNICAST DISCOVERY OPTIONS

       table_id
              Each  table  must begin with a unique, positive table ID.  The port that claims a given table does
              so by including the ID as the value of its 'unicast_master_table' option.

       logQueryInterval
              This option configures the time to wait between unicast negotiation attempts.  It is specified  as
              a power of two in seconds.  The default is 0 (1 second).

       peer_address
              This  option  specifies  the  unicast  address  of  the  peer  for use with the peer to peer delay
              mechanism.  If specified, the port owning the table will negotiate unicast  peer  delay  responses
              from  the  machine  at the given remote address, otherwise the port will send multicast peer delay
              requests.

       L2|UDPv4|UDPv6
              Each table entry specifies the transport type and network address of a  potential  remote  master.
              If multiple masters are specified, then unicast negotiation will be performed with each if them.

TIME SCALE USAGE

       ptp4l  as  domain  master either uses PTP or UTC time scale depending on time stamping mode.  In software
       and legacy time stamping modes it announces Arbitrary time scale mode, which is effectively UTC here,  in
       hardware time stamping mode it announces use of PTP time scale.

       When ptp4l is the domain master using hardware time stamping, it is up to phc2sys to maintain the correct
       offset between UTC and PTP times. See phc2sys(8) manual page for more details.