Ethernet Event 1
Ethernet Event 2
Ethernet Event 1
Rollover Event
Ethernet Event 2
…
Entry 1
Entry 2
Entry 3
Entry 16
Entry 15
EVENT FIFO
Rollover Event
Entry 4
Functional Description
14.3.7.2.4.3 Time Stamp Counter Half-Rollover Event
The CPTS includes a time stamp counter half-rollover event. The half-rollover event indicates to software
that the time stamp value has incremented from 0x7FFF_FFFF to 0x8000_0000. The half-rollover event is
included to enable software to correct a misaligned event condition.The half-rollover event is included to
enable software to determine the correct time for each event that contains a valid time stamp value – such
as an Ethernet event. If an Ethernet event occurs around a counter rollover (full rollover), the rollover
event could possibly be loaded into the event FIFO before the Ethernet event, even though the Ethernet
event time was actually taken before the rollover. Figure 3 below shows a misalignment condition.
This misaligned event condition arises because an ethernet event time stamp occurs at the beginning of a
packet and time passes before the packet is determined to be a valid synchronization packet. The
misaligned event condition occurs if the rollover occurs in the middle, after the packet time stamp has
been taken, but before the packet has been determined to be a valid time sync packet.
Figure 14-11. Event FIFO Misalignment Condition
Host software must detect and correct for misaligned event conditions. For every event after a rollover and
before a half-rollover, software must examine the time stamp most significant bit. If bit 31 of the time
stamp value is low (0x0000_0000 through 0x7FFF_FFFF), then the event time stamp was taken after the
rollover and no correction is required.
If the value is high (0x8000_0000 through 0xFFFF_FFFF), the time stamp value was taken before the
rollover and a misalignment is detected. The misaligned case indicates to software that it must subtract
one from the upper count value stored in software to calculate the correct time for the misaligned
event.The misaligned event occurs only on the rollover boundary and not on the half-rollover boundary.
Software only needs to check for misalignment from a rollover event to a half-rollover event.
14.3.7.2.4.4 Hardware Time Stamp Push Event
There are four hardware time stamp inputs (HW1/4_TS_PUSH) that can cause hardware time stamp push
events to be loaded into the Event FIFO. Each hardware time stamp input is internally connected to the
PORTIMERPWM output of each timer as shown in Figure 4.
1230
Ethernet Subsystem
SPRUH73H – October 2011 – Revised April 2013
Copyright © 2011–2013, Texas Instruments Incorporated