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.