Precision Time Protocol(PTP)

.. _ptp_interface:

Precision Time Protocol (PTP)
#############################

.. contents::
    :local:
    :depth: 2

Overview
********

PTP is a network protocol implemented in the application layer, used to synchronize
clocks in a computer network. It's accurate up to less than a microsecond.
The stack supports the protocol and procedures as defined in the `IEEE 1588-2019 standard`_
(IEEE Standard for a Precision Clock Synchronization Protocol
for Networked Measurement and Control Systems). It has multiple profiles,
and can be implemented on top of L2 (Ethernet) or L3 (UDP/IPv4 or UDP/IPv6).
Its accuracy is achieved by using hardware timestamping of the protocol packets.

Zephyr's implementation of PTP stack consist following items:

* PTP stack thread that handles incoming messages and events
* Integration with ptp_clock driver
* PTP stack initialization executed during system init

The implementation automatically creates PTP Ports (each PTP Port corresponds to unique interface).

Supported features
******************

Implementation of the stack doesn't support all features specified in the standard.
In the table below all supported features are listed.

.. csv-table:: Supported features
   :header: Feature, Supported
   :widths: 50,10

    Ordinary Clock, yes
    Boundary Clock, yes
    Transparent Clock,
    Management Node,
    End to end delay mechanism, yes
    Peer to peer delay mechanism,
    Multicast operation mode,
    Hybrid operation mode,
    Unicast operation mode,
    Non-volatile storage,
    UDP IPv4 transport protocol, yes
    UDP IPv6 transport protocol, yes
    IEEE 802.3 (Ethernet) transport protocol,
    Hardware timestamping, yes
    Software timestamping,
    TIME_RECEIVER_ONLY PTP Instance, yes
    TIME_TRANSMITTER_ONLY PTP Instance,

Supported Management messages
*****************************

Based on Table 59 from section 15.5.2.3 of the IEEE 1588-2019 following management TLVs
are supported:

.. csv-table:: Supported management message's IDs
   :header: Management_ID, Management_ID name, Allowed actions
   :widths: 10,40,25

    0x0000, NULL_PTP_MANAGEMENT, GET SET COMMAND
    0x0001, CLOCK_DESCRIPTION, GET
    0x0002, USER_DESCRIPTION, GET
    0x0003, SAVE_IN_NON_VOLATILE_STORAGE, -
    0x0004, RESET_NON_VOLATILE_STORAGE, -
    0x0005, INITIALIZE, -
    0x0006, FAULT_LOG, -
    0x0007, FAULT_LOG_RESET, -
    0x2000, DEFAULT_DATA_SET, GET
    0x2001, CURRENT_DATA_SET, GET
    0x2002, PARENT_DATA_SET, GET
    0x2003, TIME_PROPERTIES_DATA_SET, GET
    0x2004, PORT_DATA_SET, GET
    0x2005, PRIORITY1, GET SET
    0x2006, PRIORITY2, GET SET
    0x2007, DOMAIN, GET SET
    0x2008, TIME_RECEIVER_ONLY, GET SET
    0x2009, LOG_ANNOUNCE_INTERVAL, GET SET
    0x200A, ANNOUNCE_RECEIPT_TIMEOUT, GET SET
    0x200B, LOG_SYNC_INTERVAL, GET SET
    0x200C, VERSION_NUMBER, GET SET
    0x200D, ENABLE_PORT, COMMAND
    0x200E, DISABLE_PORT, COMMAND
    0x200F, TIME, GET SET
    0x2010, CLOCK_ACCURACY, GET SET
    0x2011, UTC_PROPERTIES, GET SET
    0x2012, TRACEBILITY_PROPERTIES, GET SET
    0x2013, TIMESCALE_PROPERTIES, GET SET
    0x2014, UNICAST_NEGOTIATION_ENABLE, -
    0x2015, PATH_TRACE_LIST, -
    0x2016, PATH_TRACE_ENABLE, -
    0x2017, GRANDMASTER_CLUSTER_TABLE, -
    0x2018, UNICAST_TIME_TRANSMITTER_TABLE, -
    0x2019, UNICAST_TIME_TRANSMITTER_MAX_TABLE_SIZE, -
    0x201A, ACCEPTABLE_TIME_TRANSMITTER_TABLE, -
    0x201B, ACCEPTABLE_TIME_TRANSMITTER_TABLE_ENABLED, -
    0x201C, ACCEPTABLE_TIME_TRANSMITTER_MAX_TABLE_SIZE, -
    0x201D, ALTERNATE_TIME_TRANSMITTER, -
    0x201E, ALTERNATE_TIME_OFFSET_ENABLE, -
    0x201F, ALTERNATE_TIME_OFFSET_NAME, -
    0x2020, ALTERNATE_TIME_OFFSET_MAX_KEY, -
    0x2021, ALTERNATE_TIME_OFFSET_PROPERTIES, -
    0x3000, EXTERNAL_PORT_CONFIGURATION_ENABLED,
    0x3001, TIME_TRANSMITTER_ONLY, -
    0x3002, HOLDOVER_UPGRADE_ENABLE, -
    0x3003, EXT_PORT_CONFIG_PORT_DATA_SET, -
    0x4000, TRANSPARENT_CLOCK_DEFAULT_DATA_SET, -
    0x4001, TRANSPARENT_CLOCK_PORT_DATA_SET, -
    0x4002, PRIMARY_DOMAIN, -
    0x6000, DELAY_MECHANISM, GET
    0x6001, LOG_MIN_PDELAY_REQ_INTERVAL, GET SET

Enabling the stack
******************

The following configuration option must me enabled in :file:`prj.conf` file.

- :kconfig:option:`CONFIG_PTP`

Testing
*******

The stack has been informally tested using the
`Linux ptp4l <http://linuxptp.sourceforge.net/>`_ daemons.
The :zephyr:code-sample:`PTP sample application <ptp>` from the Zephyr
source distribution can be used for testing.

.. _IEEE 1588-2019 standard:
   https://standards.ieee.org/ieee/1588/6825/

API Reference
*************

.. doxygengroup:: ptp