R21 Calculation - 8.12 English - PG056

To calculate the cable delay for a particular link instance, measure, or infer the frame timing at the output and input of the master (in the case of T₁₄) and at the input and output of the slave (in the case of T_offset). Use the T₁₄ and T_offset times to calculate cable delay, as described in section 4.2.9 of the CPRI Specification v7.0.

The general procedure for calculating T₁₄ or T_offset is:

1. Measure the coarse value using the R21 Coarse Timer.
2. Correct the coarse value for delays between the timer and the pins of the transceiver.

For 8b10b line rates

16-bit datapath cores, one datapath clock equates to 20 UI and for 32-bit datapath cores, one datapath clock equates to 40 UI.

For 64b66b line rates

32-bit datapath cores, one datapath clock equates to 33 UI and for 64-bit datapath cores, one datapath clock equates to 66 UI.