In revision D and prior, If for some reason (physical disconnect or intermediate signal degradation) the port connection between IEEE-1394 Beta ports lose synchronization, the PHY will transition the port connection from P2:Active state to P0:Disconnected and a minimum reconnect time of approximately 500 milliseconds is required. IEEE-1394-2008 section 13.3.2.1.2 Resynchronization procedure touches on resynchronization when a port determines synchronization has been lost, however it doesn’t fully define it. This enhancement to the IEEE-1394-2008 Standard fully defines the resynchronization procedure, Fast-Retrain. The Fast-Retrain process has the potential to speed up the loss of connection time from approximately 500 milliseconds to a few hundred microseconds. The Fast-Retrain enhancement allows an IEEE-1394 Beta connection to attempt to retrain a connection that has lost synchronization by attempting to immediately train the connection at the previously connected data rate.

Figure 13-1 Fast-Retrain Port Connection State Machine Changes

P2:P14

If Fast-Retrain is enabled (fast_resync = 1) and the port detects a loss of synchronization (!rxOk && !suspendRequest && !disableRequest && fast_resync) the port transitions from the P2:Active to the P14: Start Retrain state.

P14: Start Retrain

In the P14: Start Retrain state 2 to 16 ARB_CONTEXT characters are sent before transitioning to the P11:Untested state. The transmission of ARB_CONTEXT characters are sent in case the port was transmitting a packet when the loss of synchronization occurred.

P14:P11

Upon entry into the P11:Untested state the port immediately starts the training process at the previously connected data rate. For this reason, the tone based speed negotiation is not required and transmission of 8b10b symbols can begin immediately. After this point the normal Untested state process is followed.

If the retrain process doesn’t complete after DISCONNECTED_TONE_INTERVAL (42.66 to 48 milliseconds) the ports will force disconnect and transition through the P12:Loop Disabled state to P0:Disconnected.