I have a board that uses DP83848-EP in RMII mode.
I am connecting following signals from DP83848-EP to processor MAC
TX_EN
TXD[1:0]
RX_ER (optional for Mac)
CRS_DV
RXD[1:0]
25MHZ_OUT
The datasheet mentions the following for 25MHZ_OUT (pin 25).
"In RMII mode, this pin provides a 50 MHz clock output to the system."
However, using 25MHZ_OUT is not working properly. It is intermittent as it only works sometimes. The datasheet also indicates there could be 8ns max propogation delay between X1 Input and 25Mhz_OUT output. Also, there could be 2 to 14 ns output delay from X1 rising to RXD;1:0], RX_DV outputs. Since the RMII clock is 50MHz (20ns) these delays (X1 to 25MHZ_OUT and RXD[1:0]) could not guarantee timing since the clock period is only 20ns.
What is the reference clock on the RMII interface that needs to be connected to the MAC? Is it X1 or 25Mhz_OUT? It looks like reference clock for RMII should be X1. I tried putting jumper wire to use the X1 as reference clock and it works.
