Xilinx UG492 manual Setting up SourcePortIdentity and Default TX PTP Messages

Software System Integration

You should also update the following #define if there is a known asymmetry in the propagation delay on the link. This #define models the per-port global variable “delayAsymmetry” as defined in IEEE P802.1AS and should be edited based on the description given in this specification. However, the current implementation uses truncated nanoseconds rather than the scaled Ns type. The value is set to 0 by default.

#define XAVB_PROP_DELAY_ASYMMETRY 0

Setting up SourcePortIdentity (and Default TX PTP Messages)

The TX Packet buffers are pre-initialized with default values for all of the possible fields in each message. However, in order for the Ethernet AVB Endpoint software drivers to run correctly the following fields need to be written with sensible values.

•sourcePortIdentity in all TX PTP default messages

•grandmasterIdentity in TX PTP Announce message

•pathSequence (ClockIdentity[1]) in TX PTP Announce message

The example design xavb_example.c provides a simple mechanism to achieve this using the following #defines.

#define ETH_SOURCE_ADDRESS_EUI48_HIGH 0xFFEEDD #define ETH_SOURCE_ADDRESS_EUI48_LOW 0xCCBBAA

You can edit the #defines above to be the Ethernet Source Address for the device and the example software then provides code that translates this address into an XAvb_PortIdentity struct. The function XAvb_SetupSourcePortIdentity() is called with the XAvb_PortIdentity struct and writes it to the appropriate fields in the TX PTP Buffer. Additionally it stores it in the XAvb struct as the following member:

/** Contains the local port Identity information */ XAvb_PortIdentity portIdLocal;

The example software also provides an example of how to write the Ethernet Source

Address into all TX PTP packet buffers.

Setting up GrandMaster Discontinuity Callback Handler

The Ethernet AVB Endpoint software defines a callback routine which is called when the endpoint switches between being a Master and a Slave (or vice versa), or when it loses PTP lock. The application software must define a callback handler for this otherwise an error will be asserted. The example software provides an example of this as follows:

/** Function Prototype */

static void GMDiscontinuityHandler(void *CallBackRef, unsigned int TimestampsUncertain);

/** Main function in this example */ main() {

/** ... */

XAvb_Config *AvbConfigPtr;

/** Setup the handler that will be called if the PTP drivers * identify a possible discontinuity in GrandMaster time. */

XAvb_SetGMDiscontinuityHandler(&Avb, GMDiscontinuityHandler, &Avb);

/** ... */ /*****************************************************************/ /**

Ethernet AVB Endpoint User Guide www.xilinx.com 135

UG492 July 23, 2010