Changes between Version 18 and Version 19 of timesync


Ignore:
Timestamp:
05/20/2025 10:01:12 PM (10 days ago)
Author:
Tim Harvey
Comment:

added TI DP83867 PHY notes

Legend:

Unmodified
Added
Removed
Modified

  • timesync

    v18 v19  
    1515 * '''software-only PTP (lowest accuracy)''': relies on the OS to timestamp PTP even messages as they pass through the network statck without requiring hardware support for precise timestamping. This is supported in the kernel with timestamps based on the system clock rather than a dedicated PTP Hardware Clock (PHC)
    1616 * '''MAC timestamping''': if supported by MAC, this allows captured timestamps to be inserted by the hardware via a dedicated PTP Hardware Clock (PHC) at the MAC layer which reduces latency introduced by the network stack and queuing ensuring high accuracy.
    17  * '''PHY timestamping (highest accuracy)''': if supported by PHY, this allows timestamps to be captured as frames pass through the PHY minimizing latency and jitter compared to MAC-only timestamping.
     17 * '''PHY timestamping (highest accuracy)''': if supported by PHY, this allows timestamps to be captured as frames pass through the PHY minimizing latency and jitter compared to MAC-only timestamping. As an example the TI DP83867 PHY can raise a Start of Frame (SFD) signal at the beginning of every frame received which if connected to a CPU GPIO can be captured and timestamped allowing the MAC or upper layers to then apply that timestamp of to a received 1588 packet.
    1818
    1919The Linux kernel has IEEE 1588 PTP support for a handful of ethernet devices.
    … …  
    2525- IMX8MP EQOS ethernet MAC
    2626- LAN7430 PCIe Gigabit Ethernet controller MAC/PHY (used as an additional ethernet device on boards)
     27- TI DP83867 PHY supports PTP via Start of Frame Detect (SFD) which it can transmit on its GPIO_0 or GPIO_1 pins (connected on the GW74xx and GW82xx). The DP83867 will raise the SFD signal at the beginning of every frame received (where as the MAC inteprets 1588 packets). See [https://www.ti.com/lit/an/snla242/snla242.pdf TI SNLA242 App note] for details
    2728
    2829The NXP FEC MAC and EQOS supports timestamping at the MAC layer and achieves sub-microsecond synchronization accuracy, suitable for industrial automation, automotive, and IoT applications. The iMX8M’s improved timer and driver support offer slightly better precision than the iMX6, especially in modern Linux kernels. Both MAC's additionally have GPIO support where PTP-related timing signals (ie Pulse-per-Second or event triggers) can be pinmuxed to specific GPIO's and made available if supported by the individual board design.