RTL8211E: This is hardware limitation, so PTP not supported by HW

root@OpenWrt:~# ethtool -T eth0
Time stamping parameters for eth0:
software-system-clock (SOF_TIMESTAMPING_SOFTWARE)
PTP Hardware Clock: none
Hardware Transmit Timestamp Modes: none
Hardware Receive Filter Modes: none

What is PTP?

Precise Time Protocol is a Precise Time Protocol

Ii. Why does PTP occur?

We must be aware of the existence of NTP, but the accuracy of NTP is very low, can only reach the level of accuracy of milliseconds, so PTP is to overcome the problem of LOW ACCURACY of NTP

Does PTP require hardware support?

Yes, a time-dependent module needs to be integrated in the Ethernet controller, i.e. the network card needs to support PTP. For example, NXP's LS1028A chip integrates an IEEE 1588 timer module in its Ethernet controller subsystem

What is the composition of PTP in software?

PTP under Linux is composed of the following two parts:

The Linux kernel supports PTP hardware drivers (which is a feature of the Linux kernel)+ Linux user space program Linux PTP Project

How to check whether the network card supports PTP?

Use the following command to check:

Ethtool -t eth0

The output of this command is as follows:

Time stamping parameters for eth0:


The hardware - the transmit (SOF_TIMESTAMPING_TX_HARDWARE)

Software - the transmit (SOF_TIMESTAMPING_TX_SOFTWARE)

The hardware - the receive (SOF_TIMESTAMPING_RX_HARDWARE)

Software - the receive (SOF_TIMESTAMPING_RX_SOFTWARE)

Software - the system - the clock (SOF_TIMESTAMPING_SOFTWARE)

The hardware - raw - clock (SOF_TIMESTAMPING_RAW_HARDWARE)

Inhibits PTP Hardware Clock: 1

The Hardware Transmit Timestamp Modes:



The Hardware the Receive Filter Modes:



Output similar to the above information, indicating that the network card supports PTP

Where is the error caused by PTP calculation caused by network card? (PHC: inhibits PTP Hardware Clock)

Take a look at the picture below:

As can be seen from the figure, if the timestamp is generated at the application layer, the time consumption in the process of transmitting the packet down will cause significant accuracy errors.

How accurate can PTP be?

Microseconds to submicroseconds

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