AM335x Common Platform Time Sync

AM335x 有兩個 GMII 埠 (ZCE 包裝只有一個)，內建有 3 埠 Ethernet Switch 跟 SoC 其它部份連接，驅動程式使用 cpsw (CONFIG_CPSW)。並且支援 PTP，需要開啟 CONFIG_TI_CPTS (TI Common Platform Time Sync Support)，會連帶開啟 CONFIG_PTP_1588_CLOCK 及 CONFIG_PPS。

參考

1. AM335x Ethernet
2. https://www.creative-technologies.de/implementation-and-performance-analysis-of-precision-time-protocol-on-linux-based-system-on-chip-platform/ 
3. https://github.com/jeffegg/beaglebone/blob/master/Documentation/ptp/ptp.txt
4. https://training.ti.com/ptp-procsdk-linux-ptp-on-linux
5. https://issuu.com/ajintom/docs/gps_ptp_timesync_report