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

Provided by: linuxptp_4.2-1ubuntu2_amd64

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 clientOnly 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 clientOnly option may be set using either of these two forms.

              --clientOnly 1   --clientOnly=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

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

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).

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

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.

delay_mechanism
Select the delay mechanism. Possible values are E2E, P2P, NONE and Auto. The default is E2E.

delay_response_timeout
The number of delay response messages that may go missing before triggering a synchronization
fault. Setting this option to zero will disable the delay response timeout. The default is 0 or
disabled.

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.

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.

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).

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

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 "G.8275.x". 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.

hybrid_e2e
Enables the "hybrid" delay mechanism from the draft Enterprise Profile. When enabled, ports in the
client state send their delay request messages to the unicast address taken from the server's
announce message. Ports in the server 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).

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.

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.

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 server who does not need to calculate offset from
client. 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).

logAnnounceInterval
The mean time interval between Announce messages. A shorter interval makes ptp4l react faster to
the changes in the client/server 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).

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).

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).

masterOnly
This option is deprecated and will be removed in a future release. Use "serverOnly" instead.

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.

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.

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

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).

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 client 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).

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 client port will request the remote
server 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).

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

phc_index
Specifies the index of the PHC to be used for synchronization with hardware timestamping. This
option is useful with virtual clocks running on top of a free-running physical clock (created by
writing to /sys/class/ptp/ptp*/n_vclocks). The default is -1, which means the index will be set
to the PHC associated with the interface, or the device specified by the -p option.

power_profile.2011.grandmasterTimeInaccuracy
Specifies the time inaccuracy of the GM in nanoseconds. Relevant only when power_profile.version
is 2011. This value may be changed dynamically using the POWER_PROFILE_SETTINGS_NP management
message. The default is -1 meaning unknown inaccuracy.

power_profile.2011.networkTimeInaccuracy
Specifies the time inaccuracy of the network in nanoseconds. Relevant only when
power_profile.version is 2011. This value may be changed dynamically using the
POWER_PROFILE_SETTINGS_NP management message. The default is -1 meaning unknown inaccuracy.

power_profile.2017.totalTimeInaccuracy
Specifies the sum of the GM, network, and local node inaccuracies in nanoseconds. Relevant only
when power_profile.version is 2017. This value may be changed dynamically using the
POWER_PROFILE_SETTINGS_NP management message. The default is -1 meaning unknown inaccuracy.

power_profile.grandmasterID
Specifies an optional, non-zero identification code for the GM. Note that the code is an
arbitrary, power profile specific integer, not necessarily related to the clockIdentity in any
way. This value may be changed dynamically using the POWER_PROFILE_SETTINGS_NP management
message. The default is 0 meaning unused.

power_profile.version
Specifies the power profile version to be used. Valid values are "none", "2011", or "2017". This
value may be changed dynamically using the POWER_PROFILE_SETTINGS_NP management message. The
default is "none".

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.

serverOnly
Setting this option to one (1) prevents the port from entering the client 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.

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.

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.

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.

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.

PROGRAM AND CLOCK OPTIONS

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'.

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).

BMCA This option enables use of static roles for server and client devices instead of running the best
master clock algorithm (BMCA) described in 1588 profile. This can be used to speed up the start
time for servers and clients 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 clientOnly will be
used to determine the server or client role for the device. In a bridge, clientOnly (which is a
global option) can be set to make all ports assume the client role. masterOnly (which is a per-
port config option) can then be used to set individual ports to take on the server role. The
default value is 'ptp' which runs the BMCA related state machines.

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 server. The
default is 0 (disabled).

clientOnly
The local clock is a client-only clock if enabled. The default is 0 (disabled).

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

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

clock_class_threshold
The maximum clock class value from master, acceptible to sub-ordinate clock beyond which it moves
out of lock state. The default value is 248.

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"

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" and "refclock_sock" for the
NTP SHM and chrony SOCK reference clocks respectively to allow another process to synchronize the
local clock, 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".

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".

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

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.

first_step_threshold
The maximum offset the servo will correct by changing the clock frequency (phase when using nullf
servo) 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.

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).

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 "G.8275.x". The default value is 128.

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).

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 server and the client does not have any way to know
the server's identity. The default is 0 (disabled).

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 client because it has no way to identify the server in the Sync and Follow_Up messages. The
default is 0 (disabled).

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.

interface_rate_tlv
When the client and server are operating are operating at different interface rate, delay
asymmetry caused due to different interface rate needs to be compensated. The server sends its
interface rate using interface rate TLV as per G.8275.2 Annex D. The default is 0 (does not
support interface rate tlv).

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.

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).

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

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

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.

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.

message_tag
The tag which is added to all messages printed to the standard output or system log. If the tag
contains the string "{level}", it will be replaced with the log level of the message as a number.
The default is an empty string (which cannot be set in the configuration file as the option
requires an argument).

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).

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

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

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_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.

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_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_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_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.

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 ";;".

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

ptp_minor_version
This option sets the minorVersionPTP in the common PTP message header. The default is 1.

refclock_sock_address
The address of the UNIX domain socket to be used by the refclock_sock servo. The default is
/var/run/refclock.ptp.sock.

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 ";;".

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. If the
frequency correction set by ptp4l changes unexpectedly between updates of the clock (e.g. due to
another process trying to control the clock), a warning message will be printed. When set to 0,
the sanity check is disabled. The default is 200000000 (20%).

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 'servo_num_offset_values' offsets are all below the
threshold value. The default value of offset_threshold is 0 (disabled).

slave_event_monitor
Specifies the address of a UNIX domain socket for event monitoring. A local monitoring 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).

slaveOnly
This option is deprecated and will be removed in a future release. Use "clientOnly" instead.

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.

step_threshold
The maximum offset the servo will correct by changing the clock frequency (phase when using nullf
servo) 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.

step_window
When set, indicates the number of Sync events after a clock step that the clock will not do any
frequency or step adjustments. This is used in situations where clock stepping is unable to
happen instantaneously so there is a lag before the timestamps can settle properly to reflect the
clock step. The default is 0 (disabled).

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).

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.

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.

time_stamping
The time stamping method to be used. The allowed values are hardware, software, legacy, onestep,
and p2p1step. The default is hardware.

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

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 10.

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.

uds_file_mode
File mode of the UNIX domain socket used for receiving local management messages. The mode should
be specified as an octal number, i.e. it should start with a 0 literal. The default mode is 0660.

uds_ro_address
Specifies the address of the second UNIX domain socket for receiving local management messages,
which is restricted to GET actions and does not forward messages to other ports. Access to this
socket can be given to untrusted applications for monitoring purposes. The default is
/var/run/ptp4lro.

uds_ro_file_mode
File mode of the second (read-only) UNIX domain socket used for receiving local management
messages. The mode should be specified as an octal number, i.e. it should start with a 0 literal.
The default mode is 0666.

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

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.

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

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

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

       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.

       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.

TIME SCALE USAGE

       When  ptp4l  acts  as  the  domain server, it either uses the PTP or the 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 server 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.

KTHREAD PRIORITY

       In case of following log,

              timed  out  while  polling  for tx timestamp increasing tx_timestamp_timeout or increasing kworker
              priority may correct this issue, but a driver bug likely causes it

       one possible cause is that the kworker which processes timestamps is being  starved.   The  system  admin
       might try manually increasing the priority of the kworker.

       Many device drivers use kworker threads created by the PTP stack.  Such kworkers are named:
              ptp<decimal number of clock>

       The system admin can manually bump the priority of the kworker process using chrt.

       Example:
              pgrep -f "ptp[0-9]+" | xargs -I {} sudo chrt -f --pid 75 {}

       Intel ice driver may create multiple kworkers for one physical NIC and names those processes differently.

       Example for Intel E810 card:
              pgrep -f ice-ptp | xargs -I {} sudo chrt -f --pid 75 {}

       Assigning  priority  needs  careful  consideration  as assigning too high priority to any task might make
       system unstable.