Xilinx LogiCORE IP Ethernet AVB Endpoint v2.4 User Manual page 84

Chapter 9: Precise Timing Protocol Packet Buffers
Despite the logic and formatting of each individual PTP buffer being identical, the block
RAM is pre-initialized at device configuration to hold template copies of each of the PTP
frames, as indicated in
use. PTP Buffer number 8 is currently unused and could therefore be used by proprietary
applications.
The
eight Tx PTP Buffers are to be transmitted. It is possible to request more than a single frame
at one time (indeed it is possible to request all 8). When more than one frame is requested,
the Tx PTP Buffer logic will give a priority order to the lowest PTP Buffer Number that has
been requested.
The
by the software drivers to determine which of the previously requested PTP frames have
been sent, and which are still queued.
Following transmission completion of each requested PTP frame, a dedicated interrupt
signal, interrupt_ptp_tx, will be generated by the core. On the assertion of the
interrupt, the captured timestamp will already be available in the upper four bytes of the
buffer, and the tx_packet field of
most recently transmitted Buffer Number.
The
will use this interface to periodically, as defined by the IEEE802.1AS protocol, update
specific fields within the PTP packets, and request transmission of these packets.
X-Ref Target - Figure 9-1
84
Figure
"Tx PTP Packet Control Register"
"Tx PTP Packet Control Register"
"Software Drivers" provided with the core, using the PLB and dedicated interrupts,
Tx PTP Packet Buffers
Buffer Number
7
6
Signaling Frame
5 Announce Frame
4 Pdelay_Resp_Follow_Up
Frame
3 Pdelay_Resp Frame
2 Pdelay_Req Frame
1 Follow_Up Frame
0 Sync Frame
Figure 9-1: Tx PTP Packet Buffer Structure
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9-1. This shows that the first seven memory segments are in
is defined for the purpose of requesting which of the
also contains a frame waiting field. This can be read
the"Tx PTP Packet Control Register"
Buffer Base Address
Single Tx PTP Packet Buffer
0x1700
0x1600
0x1500
0x1400
0x1300
0x1200
0x1100
0x1000
will indicate the
Address (+ Buffer Base Address)
timestamp[31:24] 0xFF
timestamp[23:16] 0xFE
timestamp[15:8] 0xFD
timestamp[7:0] 0xFC
unused
0x08 + frame_length_field
PTP Frame Data
0x08
reserved
frame_length_field 0x00
byte-wide data
Ethernet AVB Endpoint User Guide
UG492 September 21, 2010