Hi,
We are planning to use KSZ9031 with AM3352. I have seen few posts related to this Micrel PHY in which timing was the issue. As per my understanding according to the RGMII standards following parameters for receiver and transmitter are present –
Data to clock skew at transmitter (TSKEWT) = +500ps.
Data to clock skew at receiver (TSKEWR) = 1.0ns to 2.6ns
This is also provided in datasheets of KSZ9031 and AM3352. Also the setup time requirement given in the datasheets is 1ns minimum. As the data in RGMII mode is DDR we will have data width of 3.6ns.
Assuming that the data and clock are launched at same edge and are reaching the receiver at the same edge (neglecting the routing delays). We have a setup requirement of minimum 1ns, we need to shift the clock edge by 1ns to meet it.
So we have a valid data window of 1ns to 2.6ns by which the clock edge could be shifted for meeting timings. Now as at the transmitter itself there will be a skew of +500ps. We need to provide a delay of 1.5ns (0.5+1) in clock for placing the clock edge at the starting of data window. And for placing it in middle we need around 1.8ns of delay on clock.
Please confirm if my understanding on timing calculation is correct.
Also as KSZ9031 already provides a delay of 1.2ns on clock being sent to AM3352 so we need to provide only a skew of 0.6ns (1.8ns – 1.2ns). But on clock sent from AM3352 as there are no delays available so we need to provide full 1.8ns skew on clock when it reaches PHY?
Thanks & Regards,
Nikhil
