The input CTL_TX_RETRANS_DEPTH (which is set through the DRP interface)
is used to set the maximum number of eight Interlaken word entries to be stored in the
retransmission buffer. This value should be between two and three times the greater of
the values assigned to CTL_RX_RETRANS_TIMER1 and
CTL_RX_RETRANS_TIMER2 and then divided by eight.
For example, if CTL_RX_RETRANS_TIMER1 has a value of 20 and
CTL_RX_RETRANS_TIMER2 has a value of 2000, the
CTL_TX_RETRANS_DEPTH should be set to a value of about 625.
Similarly, if CTL_RX_RETRANS_TIMER1 has a value of 2500 and
CTL_RX_RETRANS_TIMER2 has a value of 0, the
CTL_TX_RETRANS_DEPTH should be set to a value of about 782.
There must be sufficient depth in the TX retransmission buffer to contain at least five different sequence numbers when maximum sized bursts are stored. The total number of bursts required is affected by the multiplier in use. Thus, the minimum depth of the TX retransmission buffer can be found by satisfying the following equation:
For example, if the multiplier is 1, the minimum number of entries required for the retransmission buffer depth is 21. If the multiplier is 2, the minimum number of entries required for the retransmission buffer depth is 42, and so forth.
Generally, the minimum depth requirement is easily met by the latency in the system.