K60P100M100SF2RM Datasheet, PDF (1207/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Chapter 44 10/100-Mbps Ethernet MAC (ENET)
Through dedicated correction logic, the timer can be adjusted to allow synchronization to
a remote master and provide a synchronized timing reference to the local system. The
timer can be configured to cause an interrupt after a fixed time period to allow
synchronization of software timers or perform other synchronized system functions.
The timer is usually used to implement a period of one second; hence, its value ranges
from 0 to (1 × 10⁹)-1. The period event can trigger an interrupt and software can maintain
the seconds and hours time values as necessary.
44.4.10.1.1 Adjustable Timer Implementation
The adjustable timer consists of a programmable counter/accumulator and a correction
counter. The periods of both counters and its increment rate are freely configurable
allowing very fine tuning of the timer.
Adjustable
Timer
Counter
ENET_ATPER
mod
Correction
counter
ENET_ATCOR ENET_ATINC ENET_ATINC
[INC_CORR]
[INC]
External free-running
counter
To MAC
ENET_ATCR
[SLAVE]
Figure 44-60. Adjustable Timer Implementation Detail
The counter produces the current time. During each time-stamping clock cycle a constant
value is added to the current time as programmed in ENETn_ATINC. The value depends
on the chosen time-stamping clock frequency. For example, if it operates at 125 MHz
setting the increment to eight represents 8 ns.
The period, configured in ENETn_ATPER, defines the modulo when the counter wraps.
In a typical implementation the period is set to 1 × 10⁹ so the counter wraps every
second, and hence all timestamps represent the absolute nanoseconds within the one
second period. When the period is reached, the counter wraps to start again respecting the
period modulo. This means it does not necessarily start from zero, but instead the counter
is loaded with the value (Current + Inc –(1 × 10⁹)), assuming the period is set to 1 × 10⁹.
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.
1207