Curtiss-Wright FHF5-PC4MWB04-00, Hardware Reference Manual

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OPERATION
Copyright 2017 4-4 FibreXtreme Hardware Reference
4.4
Data Synchronization
The data synchronization primitive SYNC is sent across the link under user control. This
primitive synchronizes with the data stream. On the PCI variations of SL240, this is
written to the transmit FIFO under user control or through the transaction channels. On
the FPDP variations of the card, this signal is the /SYNC line on the FPDP interface. The
SYNC on PCI devices 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.
4.5
Configuration Options
There are many different configuration options available which affect the operation of the
SL240 card. Most of these options are configured in the Link Control register (described
in Appendix B).
4.5.1 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 Controls, Inc. 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.
4.5.2 Loop Enable
The loop-enable option allows the SL240 card to transmit the received Serial FPDP data
stream again. Turning on the loop enable implies that this node is designated as a receiver
in the current configuration.
Receiver/Transmitter Enable
The transmitter-enable and receiver-enable bits in the Link Control register turn off the
transmit and receive Serial FPDP data streams, respectively. Neither affects the loop
operation, so data will still be retransmitted if the loop operation is enabled. This makes
these options useful for record/playback systems where you wish to merely retransmit the
data received without processing it. The receive-enable is useful for disabling the receive
FIFO for the master in loop operation so that the data sent is not received.