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

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SL100/SL240 PROTOCOL
Copyright 2017 7-5 FibreXtreme Hardware Reference
7.4
Data Transmission and Flow Control
As SL100/SL240 is seen as a point-to-point link from the transmitter, there is no need to
log into the receiver node to begin sending data. SL100/SL240 boards can begin
transmission as soon as they are started and data is available in the Transmit FIFO. Using
the frames described above, the transmitter sets up a constant stream of frames, into
which it inserts data as it becomes available. Data is only inserted if the flow control
signal from the remote end is GO—if it is STOP, then the data waits in the Transmit FIFO
until the signal changes. Curtiss-Wright Controls’ SL100/SL240 boards use the same
protocol when transmitting from either end to allow the link to operate bi-directionally.
Since these data streams are independent, the maximum throughput on the link would be
210 MB/s (105 MB/s/direction) for SL100 or 494 MB/s for SL240.
The receiver should transmit the STOP signal when it has space for the data contained in
20 km of fiber or less left. Assuming 5 µs/km for the speed of light, this gives us 100 µs
of data. For SL100, each 32-bit word (40 bits on the link) takes 37.64 ns, there are 2657
words stored in 20 km of cable. For SL240, each 32-bit word (40 bits on the link) takes
16 ns, so there are 6250 words stored in 20 km of cable. The first 10 km is reserved for
sending the STOP signal to the transmitter, and the second 10 km is for the data already
contained in the receive fiber.