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Ethernet AVB Endpoint User Guide www.xilinx.com 131
UG492 July 23, 2010
Chapter 13
Software Drivers
Software drivers delivered with the Ethernet AVB Endpoint core provide the following
functions, which utilize the dedicated hardware within the core for the Precise Timing
Protocol (PTP) IEEE P802.1AS specification:
• Best Clock Master Algorithm (BMCA) determines whether the core should operate
in master clock or slave clock mode
• PTP Clock Master functions
• PTP Clock Slave functions that accurately synchronize the local Real Time Clock
(RTC) to match that of the network clock master
The following definitions provide only a simplistic concept of PTP protocol operation. For
detailed information about the PTP protocol, see the IEEE P802.1AS specification.
This chapter only describes the basic operation and some key components of the software
drivers. The software driver code is documented such that the comments can be viewed by
Doxygen and detailed descriptions of all aspects of the software are available throughout
the code. This should allow customers to fully understand the operation of the provided
software drivers and to edit the drivers for their own secret source applications.
Fundamentally, the slave “Real Time Clock” synchronization functions complete a
software controlled phase-locked loop. Therefore, many implementations are possible.
The provided software drivers implement a very simple software PLL implementation.
However, this has been shown in hardware to provide excellent “Real Time Clock”
synchronization results.
The document section “drivers/avb_v2_04_a/src” in Chapter 16 lists all of the C files
delivered with the Ethernet AVB Endpoint core and provides a description of how the
software is divided up between these files.
Clock Master
If the core is acting as clock master, the software drivers delivered with the core
periodically sample the current value of the RTC and transmit this value to every device on
the network using the P802.1 defined Sync and Follow-Up PTP packets.