linuxptp/ptp4l.8

.TH PTP4l 8 "April 2018" "linuxptp"
.SH NAME
ptp4l - PTP Boundary/Ordinary/Transparent Clock

.SH SYNOPSIS
.B ptp4l
[
.B \-AEP246HSLmqsv
] [
.BI \-f " config"
] [
.BI \-p " phc-device"
] [
.BI \-l " print-level"
]
[
.BI \-i " interface"
] [
.I long-options
]
.I .\|.\|.

.SH DESCRIPTION
.B 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).

.SH OPTIONS
.TP
.B \-A
Select the delay mechanism automatically. Start with E2E and switch to P2P when
a peer delay request is received.
.TP
.B \-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.
.TP
.B \-P
Select the peer delay (P2P) mechanism. A warning will be printed when a delay
request is received on port using the P2P mechanism.
.TP
.B \-2
Select the IEEE 802.3 network transport.
.TP
.B \-4
Select the UDP IPv4 network transport. This is the default transport.
.TP
.B \-6
Select the UDP IPv6 network transport.
.TP
.B \-H
Select the hardware time stamping. All ports specified by the
.B \-i
option and in the configuration file must be attached to the same PTP hardware
clock (PHC). This is the default time stamping.
.TP
.B \-S
Select the software time stamping.
.TP
.B \-L
Select the legacy hardware time stamping.
.TP
.BI \-f " config"
Read configuration from the specified file. No configuration file is read by
default.
.TP
.BI \-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.
.TP
.BI \-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.
.TP
.B \-s
Enable the slaveOnly mode.
.TP
.BI \-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).
.TP
.B \-m
Print messages to the standard output.
.TP
.B \-q
Don't send messages to the system logger.
.TP
.B \-v
Prints the software version and exits.
.TP
.BI \-h
Display a help message.

.SH 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.

.RS
\f(CW\-\-slaveOnly 1   \-\-slaveOnly=1\fP
.RE

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

.SH 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.

.TP
.B 1.
The global section (indicated as
.BR [global] )
sets the program options, clock options and default port options. Other
sections are port specific sections and they override the default port options.
.TP
.B 2.
Port sections give the name of the configured port (e.g.
.BR [eth0] ).
Ports specified in the configuration file don't need to be
specified by the
.B \-i
option. An empty port section can be used to replace the command line option.
.TP
.B 3.
Tables for configuring unicast discovery begin with
.B \%[unicast_master_table].

See UNICAST DISCOVERY OPTIONS, below.

.SH PORT OPTIONS

.TP
.B 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.
.TP
.B 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).
.TP
.B 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).
.TP
.B 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).
.TP
.B 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).
.TP
.B announceReceiptTimeout
The number of missed Announce messages before the last Announce messages
expires.
The default is 3.
.TP
.B 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.
.TP
.B transportSpecific
The transport specific field. Must be in the range 0 to 255.
The default is 0.
.TP
.B 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.
.TP
.B path_trace_enabled
Enable the mechanism used to trace the route of the Announce messages.
The default is 0 (disabled).
.TP
.B follow_up_info
Include the 802.1AS data in the Follow_Up messages if enabled.
The default is 0 (disabled).
.TP
.B 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).
.TP
.B 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.
.TP
.B delay_mechanism
Select the delay mechanism. Possible values are E2E, P2P and Auto.
The default is E2E.
.TP
.B 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).
.TP
.B 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).
.TP
.B 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).
.TP
.B 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).
.TP
.B 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.  Tables may not be shared
between ports, but nothing prevents table entries from appearing in
more than table.
The default is 0 (unicast discovery disabled).
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B network_transport
Select the network transport. Possible values are UDPv4, UDPv6 and L2.
The default is UDPv4.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B delay_filter_length
The length of the delay filter in samples.
The default is 10.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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).
.TP
.B 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
.B ptp4l
to the same subnet.

.SH PROGRAM AND CLOCK OPTIONS

.TP
.B twoStepFlag
Enable two-step mode for sync messages. One-step mode can be used only with
hardware time stamping.
The default is 1 (enabled).
.TP
.B slaveOnly
The local clock is a slave-only clock if enabled. The default is 0 (disabled).
.TP
.B 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).
.TP
.B 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.
.TP
.B 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.
.TP
.B clockClass
The clockClass attribute of the local clock. It denotes the traceability of the
time distributed by the grandmaster clock.
The default is 248.
.TP
.B clockAccuracy
The clockAccuracy attribute of the local clock. It is used in the best master
selection algorithm.
The default is 0xFE.
.TP
.B 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"
.TP
.B offsetScaledLogVariance
The offsetScaledLogVariance attribute of the local clock. It characterizes the
stability of the clock.
The default is 0xFFFF.
.TP
.B 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.

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.
.TP
.B 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.
.TP

.B domainNumber
The domain attribute of the local clock.
The default is 0.
.TP
.B utc_offset
The current offset between TAI and UTC.
The default is 37.
.TP
.B free_running
Don't adjust the local clock if enabled.
The default is 0 (disabled).
.TP
.B 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).
.TP
.B 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).
.TP
.B 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.
.TP
.B 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.
.TP
.B 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).
.TP
.B 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."
.TP
.B 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".
.TP
.B 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)
.TP
.B 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)
.TP
.B 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.
.TP
.B 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.
.TP
.B 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
.TP
.B 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.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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
.BR pi_offset_const .
.TP
.B 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
.BR pi_f_offset_const .
.TP
.B 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
.BR pi_max_frequency .
.TP
.B 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%).
.TP
.B 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.
.TP
.B ntpshm_segment
The number of the SHM segment used by ntpshm servo.
The default is 0.
.TP
.B 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.
.TP
.B uds_address
Specifies the address of the UNIX domain socket for receiving local
management messages. The default is /var/run/ptp4l.
.TP
.B 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.
.TP
.B 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.
.TP
.B 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".
.TP
.B logging_level
The maximum logging level of messages which should be printed.
The default is 6 (LOG_INFO).
.TP
.B 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).
.TP
.B verbose
Print messages to the standard output if enabled.
The default is 0 (disabled).
.TP
.B use_syslog
Print messages to the system log if enabled.
The default is 1 (enabled).
.TP
.B 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).
.TP
.B time_stamping
The time stamping method. The allowed values are hardware, software and legacy.
The default is hardware.
.TP
.B 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 ";;".
.TP
.B 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 ";;".
.TP
.B 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.
.TP
.B manufacturerIdentity
The manufacturer id which should be an OUI owned by the manufacturer.
The default is 00:00:00.
.TP
.B 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
.B step_threshold
option is set to correct such offset by stepping).
Relevant only with software time stamping. The default is 1 (enabled).
.TP
.B 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.
.TP
.B 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.
.TP
.B 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'.
.TP
.B 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.
.TP
.B 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).
.TP
.B 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).

.SH UNICAST DISCOVERY OPTIONS

.TP
.B 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.
.TP
.B 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).
.TP
.B 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.
.TP
.B 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.

.SH TIME SCALE USAGE

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

.SH SEE ALSO
.BR pmc (8),
.BR phc2sys (8)