Hello,
We are processing conflicting information on this point. The questions are:
- On the AM6442, can an external clock connected to the EXT_REFCLK1 pin be used for PTP timestamping?
- If so, what frequency should be used for optimal functionality?
The TRM suggests this is possible. Figure 12-353 and Table 5-244 show the CPTS_RFT_CLK mux with an option for EXT_REFCLK1:
However, in a related thread, a TI engineer stated that the minimum supported CPTS_RFT_CLK frequency was 125 MHz, and cited TRM Table 12-668:
If this is correct, then it's unclear how EXT_REFCLK1 can be used, because the device datasheet specifies a maximum supported frequency on this pin of 100 MHz:
It seems to us one of the following must be true:
- The ADD_VAL feature is not required for normal PTP operation;
- The TRM is wrong and the ADD_VAL feature can in fact work with clocks <= 100 MHz;
- The datasheet is wrong and EXT_REFCLK1 can in fact handle frequencies >= 125 MHz;
- The TRM is wrong and EXT_REFCLK1 is not supported for PTP timestamping (in this case we can't understand why the CPTS muxes have EXT_REFCLK1 inputs).
Thanks in advance for any clarification you can offer!
