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NTP | IEEE 1588 | |
|---|---|---|
Communication | Internet | LAN |
Accuracy | msecMillisecond | <usec< Microsecond |
H/W Support | No | Usually required, doable without |
Network Time Protocol (NTP) has been the traditional way to synchronization time over Ethernet networks. NTP allows time synchronization up to 100 milliseconds. The IEEE 1588 PTP is required to achieve tighter synchronization. In software PTP applications, single link synchronization in the range of 100 microseconds can be reached. As can be seen in Figure 2, hardware Hardware assistance is required to achieve time synchronization in the nanosecond region.
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Hardware Timestamping of PTP
Hardware TSUs time stamp unit (TSU) incorporate a time of day (TOD) accumulator that measures the passage of time by counting the cycles of a reference clock signal from a PTP hardware clock (PHC). The PHC is steered by the PTP clock servo that issues corrections (clock operations) to the PHC. The IEEE 1588 protocol stack obtains the PTP timestamp information from the hardware TSU and provides it to the clock servo. This is illustrated in Figure 3.
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The logical PHC and TSU functions can be implemented in a single silicon device, or they can be implemented in separate devices.
Check whether your NIC(Network Interface Card) supports PTP with the following command.
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Basically, just follow these steps:
1.
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Run PTP grandmaster within LAN.
PTP grandmaster has accurate time source, such as GPS, as can be seen in Figure 5.
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We run ptp4l on an PC as a PTP grandmaster to test.
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| Code Block | ||
|---|---|---|
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root@dbv3:~# ptp4l -i eth0 -s -m -H |
Pay attention to two places.
a. Check ethernet interface Check NIC at promise mode?
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If not, you can switch over manually with this command.
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Thus, SP7350 can receive all the broadcast packets.
b. Check GMAC driver.
Check 0465ns accuracy within config_addend function to fix incorrect PTP TAR register value.
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4. Check synchronization result.
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