OPERATION
6-5
FibreXtreme User GuideCopyright 2017
Note that NRDY as a Serial FPDP signal has no direct impact on the operation of the link logic.
Rather, NRDY is passed through the link logic and its function is dependent on the respective
host interface. The Serial FPDP flow control (implemented via suspend requests which are also
known as STOP ordered sets) is used by the link logic and does not directly affect the interface
between the link logic and host interface.
NOTE: One node on the loop MUST be in non-loop operation in order for loop operation to
work correctly. One node needs to remove the data from the loop. When switching masters
on the loop, both the previous master and the next master should be in non-loop operation
before the previous master switches into loop mode.
6.3 Data Synchronization
The data synchronization primitive SYNC is sent across the link under user control. This
primitive synchronizes with the data stream and is written to the transmit FIFO under user control
or through the transaction channels. The SYNC may correspond to /SYNC without /DVALID
or /SYNC with /DVALID on the FPDP interface depending on the card’s configuration.
Unless a non-intelligent device is used, such as a sensor, which cannot insert a periodic SYNC,
SYNC should always be used to segment data transfers. It has little impact on system
performance and provides a mechanism to synchronize the send and receive operations via the
link. This synchronization process is especially useful at application start-up, after error
conditions, and is also useful to verify the error-free flow of data during normal operation.
6.4 Configuration Options
The data synchronization primitive SYNC is sent across the link under user control. This
primitive synchronizes with the data stream and is written to the transmit FIFO under user control
or through the transaction channels. The SYNC may correspond to /SYNC without /DVALID
or /SYNC with /DVALID on the FPDP interface depending on the card’s configuration.
Unless a non-intelligent device is used, such as a sensor, which cannot insert a periodic SYNC,
SYNC should always be used to segment data transfers. It has little impact on system
performance and provides a mechanism to synchronize the send and receive operations via the
link. This synchronization process is especially useful at application start-up, after error
conditions, and is also useful to verify the error-free flow of data during normal operation.
6.4.1 Flow Control
Flow control allows a Serial FPDP receiver to throttle the data stream from a Serial FPDP
transmitter. If this option is turned off, the card will continue to send data even when the receiver
signals it to stop or when the link is down.
In almost every application, flow control should be enabled. Even if the application must sustain
maximum link throughput, it is better to drop the data at the sending source should the system
experience a temporary overload condition. In some rare cases, flow control is not desirable. In
these cases, very careful system planning is required, which should be confirmed with Curtiss-
Wright prior to architectural finalization. One possible exception is for applications that cannot use
a duplex fiber-optic link, which means status information (link up and state of flow control) is not
available from the remote node. In this circumstance, disable flow control to allow the transmitter
to function without the receiver connected normally.
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