SPRZ458F May 2019 – February 2024 TMS320F28384D , TMS320F28384D-Q1 , TMS320F28384S , TMS320F28384S-Q1 , TMS320F28386D , TMS320F28386D-Q1 , TMS320F28386S , TMS320F28386S-Q1 , TMS320F28388D , TMS320F28388S
Ethernet: Incorrect Flexible Pulse-per-Second (PPS) Output Interval When Fine Correction Method is Used
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The Ethernet module provides two programmable options—fine and coarse—for correcting the IEEE 1588 internal time reference. When the coarse correction method is used, the correction is applied in one shot and does not affect the flexible PPS output. When the fine correction method is used, the correction is applied uniformly and continuously to the IEEE 1588 internal time reference as well as to the flexible PPS output. However, due to this defect, when fine correction method is used and the drift in the frequency of the clock that drives the IEEE 1588 internal time reference is large (when compared with the grandmaster source clock), the flexible PPS output interval is incorrect. This does not impact the IEEE 1588 internal time reference updates.
The internal PPS counter used for generating the PPS interval is incorrectly reset earlier than expected, resulting in the next PPS cycle starting incorrectly, earlier than expected. The incorrect Flexible PPS Output Interval from the Ethernet module can cause external devices that are synchronized with the flexible PPS trigger outputs to go out of synchronization.
The application can use the coarse method for correcting the IEEE 1588 internal time reference. Because the time correction is applied in a single shot in the coarse correction method, timestamp captured for, at the most, one packet is impacted.