SNLS614A September 2018 – December 2018 DP83869HM
When the DP83869HM is operating in 1000-Mb master mode, variation of the RX_SFD pulse can be estimated using the Skew FIFO Status register (register address 0x0055) bit[7:4]. The value read from the Skew FIFO Status register bit[7:4] must be multiplied by 8 ns to estimate the RX_SFD variation added to the baseline latency.
Example: While operating in master 1000-Mb mode, a value of 0x2 is read from the Skew FIFO register bit[7:4].
2 × 8 ns = 16 ns is subtracted from the TX_SFD to RX_SFD measurement to determine the baseline latency.