Introduction

This software is an implementation of the Precision Time Protocol (PTP) according to IEEE standard 1588 for Linux. The dual design goals are to provide a robust implementation of the standard and to use the most relevant and modern Application Programming Interfaces (API) offered by the Linux kernel. Supporting legacy APIs and other platforms is not a goal.

License

The software is copyrighted by the authors and is licensed under the GNU General Public License. See the file, COPYING, for details of the license terms.

Goals and Features

• Supports hardware and software time stamping via the Linux SO_TIMESTAMPING socket option.
• Supports the Linux PTP Hardware Clock (PHC) subsystem by using the clock_gettime family of calls, including the new clock_adjtimex system call.
• Implements Boundary Clock (BC) and Ordinary Clock (OC).
• Transport over UDP/IPv4, UDP/IPv6, and raw Ethernet (Layer 2).
• Modular design allowing painless addition of new transports and clock servos.

System Requirements

In order to run this software, you need to run a recent Linux kernel version 3.0 or newer, and the kernel header files must available at compile time.

In addition, you will also need to have either:

1. A supported Ethernet MAC device.
2. A supported PHY device paired with a MAC that allows time stamping in the PHY (indicated by PHY=Y in the table below).

Linux Kernel Support

In order to support PTP, the operating system needs to provide two services: network packet time stamping and clock control. In 2009, Patrick Ohly added a new socket option called SO_TIMESTAMPING for packet time stamping, especially for PTP. This work appeared in Linux version 2.6.30.

In July of 2011, the PTP Hardware Clock (PHC) subsystem was merged into Linux version 3.0. The PHC code provides a driver framework and the user space API for clock control.

Driver Support Matrix

The table below shows the Linux drivers that support the new API. The meaning of the column abbreviations is as follows.

• SOTS: SO_TIMESTAMPING support. This comes in three flavors.
  1. RAW: Supports time stamping using the PHC time values.
  2. SW: Supports software time stamping using the system time.
  3. SYS: Supports time stamping using PHC time values scaled to the system time. This is a legacy mode and its use in new drivers is discouraged.
• PHC: PTP Hardware Clock support. These drivers will offer a character device that allows direct control of the hardware clock.
• PHY: Supports time stamping in the PHY. This indicates an Ethernet MAC driver supporting SO_TIMESTAMPING and PHC in the PHY. If you have or build a computer that combines this MAC with a PTP capable PHY, then it will work with the Linux PHC subsystem.
• VER: Linux kernel version when the PTP API support was added.

Hardware Timestamping

Driver	Hardware	SOTS	PHC	PHY	VER
bfin_mac	Analog Blackfin	SYS	N	NA	pre 3.0
igb	Intel 82576, 82580	SYS	N	NA	pre 3.0
dp83640	Nat Semi PHYTER	RAW	Y	NA	3.0
gianfar	Freescale eTSEC PowerPC	RAW	Y	NA	3.0
ptp_ixp46x	Intel IXP465	RAW	Y	NA	3.0

Software Timestamping

Driver	Hardware	SOTS	PHC	PHY	VER
davinci_emac	TI DaVinci, Sitara	SW	N	Y	3.1
dnet	Dave Ethernet MAC	SW	N	Y	3.1
emaclite	Xilinx Ethernet Lite	SW	N	Y	3.1
ethoc	OpenCores 10/100 MAC	SW	N	Y	3.1
fec	Freescale Coldfire	SW	N	Y	3.1
fec_mpc52xx	Freescale MPC5200	SW	N	Y	3.1
fs_enet	Freescale MPC512x	SW	N	Y	3.1
ixp4xx_eth	Intel IXP4xx	SW	N	Y	3.0
lib8390	Asix AX88796	SW	N	Y	3.1
lib8390	Various 8390 based HW	SW	N	N	3.1
ll_temac	Xilinx LL TEMAC	SW	N	Y	3.1
macb	Atmel AT32, AT91	SW	N	Y	3.1
mv643xx_eth	Marvell Discovery, Orion	SW	N	Y	3.1
pxa168_eth	Marvell pxa168	SW	N	Y	3.1
r6040	RDC Ethernet MAC	SW	N	Y	3.1
smsc911x	SMSC LAN911x, LAN921x	SW	N	Y	3.1
smsc9420	SMSC LAN9420 PCI	SW	N	Y	3.1
stmmac	STM Synopsys IP Core	SW	N	Y	3.1
tg3	Broadcom Tigon3 PCI	SW	N	Y	3.1
ucc_geth	Freescale QE Gigabit	SW	N	Y	3.1

Installation

Linux kernel

There are many ways of getting a precompiled Linux kernel or compiling your own, so this section is only meant as an example. It is important to have the kernel headers available when compiling the Linux PTP stack.

export ARCH=x86
export CROSS_COMPILE=
export KBUILD_OUTPUT=/home/richard/kernel/ptp_debian
mkdir -p $KBUILD_OUTPUT
cp /boot/config-2.6.38-bpo.2-686 $KBUILD_OUTPUT/.config
make oldnoconfig
make menuconfig
time make -j4
make headers_install

Here is a table of kernel configuration options needed for PTP support. In addtion to these, you should enable the specific Ethernet MAC and PHY drivers for your hardware.

Option	Description
CONFIG_EXPERIMENTAL	Required
CONFIG_PPS	Required
CONFIG_NETWORK_PHY_TIMESTAMPING	Timestamping in PHY devices
PTP_1588_CLOCK	PTP clock support

PTP stack

1. Just type ‘make’
2. If you compiled your own kernel (and the headers are not installed into the system path), then you should set the KBUILD_OUTPUT environment variable as in the example, above.
3. There is no install target. You can run the program in place or copy it into the system path, like /usr/local/bin.

Getting Involved

The software development is hosted at Source Forge.

https://sourceforge.net/projects/linuxptp/

Reporting Bugs

Please report any bugs or other issues with the software to the linuxptp-users mailing list.

https://lists.sourceforge.net/lists/listinfo/linuxptp-users

Development

If you would like to get involved in improving the software, please join the linuxptp-devel mailing list.

https://lists.sourceforge.net/lists/listinfo/linuxptp-devel

Other PTP Applications

As of yet there are no other open source applications making use of the new Linux APIs for PTP. However, patches are available for the ptpd program adapting it to the new calls. These patches do not really turn the ptpd into a perfect solution for hardware time stamping under Linux. Instead, they merely illustrate how the newer APIs work.

You can get the patches over at github. There are two branches, phc1 and phc2, for PTP versions 1 and 2, respectively.

• git://github.com/richardcochran/ptpd-phc.git
• https://github.com/richardcochran/ptpd-phc