■ Sending and receiving of PTP messages. The timestamp snapshot can be controlled through
the Ethernet MAC Timestamp Control (EMACTIMSTCTRL) register, offset 0x700. Timestamp
snapshots can be for Sync messages.
■ Maintaining the data sets such as timestamp values.
For an ordinary clock, snapshots can be taken of either version 1 or version 2 PTP types but not
both. Selecting between the two is controlled by the PTPVER2 bit of the EMACTIMSTCTRL
register.
PTP Processing and Control
There are fields in an Ethernet Payload that the Ethernet Controller can use to detect the PTP packet
type and control the snapshot to be taken. These fields are different depending on whether the PTP
frames are:
■ PTP frames over IPv4
■ PTP frames over IPv6
■ PTP frames over Ethernet
The PTPIPV4, PTPIPV6 or PTPETH bits can be set depending on which PTP processing is required.
Reference Timing Source
The MAC supports the following reference timing source features defined in the IEEE 1588-2008
standard:
■ 80-bit timestamp
■ Fixed Pulse-Per-Second PPS0 Output
■ Flexible Pulse-Per-Second PPS0 Output
80-Bit Timestamp
The MAC supports an 80-bit timestamp with a lengthened seconds integer portion which is 48-bits
wide. The Ethernet MAC System Time - Seconds (EMACTIMSEC) register at offset 0x708 and
the Ethernet MAC System Time-Higher Word Seconds (EMACHWORDSEC) register at offset
0x724 comprise the seconds count. The 32-bit Ethernet MAC System Time - Nanoseconds
(EMACTIMNANO) register contains the fractional portion of the timestamp units of nanoseconds.
The nanoseconds register supports the following two modes:
■ Digital rollover mode: In digital rollover mode, the maximum value in the nanoseconds field is
0x3B9A_C9FF, that is, (10e9-1) nanoseconds.
■ Binary rollover mode: In binary rollover mode, the nanoseconds field rolls over and increments
the seconds field after value 0x7FFF_FFFF. Accuracy is ~0.466 ns per bit.
Digital or binary rollover mode can be selected by programming the DGTLBIN bit of the
EMACTIMSTCTRL register. Note that the timestamp maintained in the MAC is still 64-bits wide,
but that the overflow to the upper 16-bits seconds register happens once in 130 years.
1447June 18, 2014
Texas Instruments-Production Data
Tiva
™
TM4C1294NCPDT Microcontroller
To Next Page
Loading...
Need help?
General
