Data Sheet

Ethernet Controller I210 —Inline Functions
348
Table 7-62. Packet Timestamp Sampling Latency at 100 Mb/s (Stand-alone Setup)
Table 7-63. Packet Timestamp Sampling Latency at 100 Mb/s (Arithmetic Mean and
Exponential Smoothing)
Figure 7-21. Timestamp Point
7.8.3.2 1588 Timer Registers: SYSTIM, TIMADJ and TIMINCA
The SYSTIM is a 96-bit register is composed of: SYSTIMR, SYSTIML and SYSTIMH registers: The
SYSTIMR register holds the sub ns fraction, the SYSTIML register holds the ns fraction and the
SYSTIMH register holds the second fraction of the time (note that the upper two bits of the SYSTIML
register are always zero while the max value of this register is 999,999,999 dec). When synchronized,
the SYSTIM registers defines the absolute time relative to PTP “epoch” which is January 1st 1970
00:00:00 International Atomic Time (TAI).
• Initial Setting - Setting the initial time is done by direct write access to the SYSTIM register.
Software should first set the SYSTIML register and then set the SYSTIMH register. Setting the
SYSTIMR register is meaningless while it represents sub ns units. It is recommended to disable the
timer at programming time as follows:
Parameter
Min/Max
Latency
Comment
Tx timestamp to
start of SFD on
MDI
984/1024 ns
Min/max values represent a possible variance over reset or link up/down events. The latency is
measured with minimal PHY FIFO depth by setting bits 15:14 in the PHY TX FIFO register (MAC
Specific Control Register 1 - Page 2, Register 16). Setting the PHY Tx FIFO to other values
increase the delay by an 8-bit time for each increment of the FIFO size.
Start of SDF on
MDI to Rx
timestamp
2148/2228 ns
The min/max numbers represent possible jitter due to synchronization between receive and
transmit clock domains.
Parameter Average Comment
Tx timestamp to start of SFD on MDI 1044 ns The range (max minus min) values measured for the Tx and Rx latency
parameters are similar to the measured parameters in a stand-alone
setup.
Start of SDF on MDI to Rx timestamp 2133 ns
Tx + Rx latency 3177 ns