8-6
FibreXtreme User Guide
APPENDIX B
Copyright 2017
8.3.1 Link Bandwidth
With CRC disabled and the Copy Mode Master bit clear (‘0’), there is a five-word overhead for
every frame transmitted. Since frames can contain up to 512 words of data, this results in an
efficiency of 99.03%. With CRC enabled and the Copy Master bit clear, there is a six-word
overhead for every frame transmitted. This results in a maximum efficiency of 98.84%. With the
Copy Mode Master bit set (‘1’), three additional ordered sets are added per frame. This results in
an efficiency of 98.46 percent without CRC and 98.27 percent with CRC. Table 6-2 gives the
theoretical maximum sustained throughput based on these numbers.
Table 6-2 Maximum Sustained Throughput per link
With CRC and
Copy Mode
Master bit = 0
Without CRC
and Copy Mode
Master bit = 0
With CRC and
Copy Mode
Master bit = 1
Without CRC and
Copy Mode
Master bit = 1
NOTE: The Copy Master Mode is located in the Link Control register.
8.3.2 FPDP Sinnal Sample Rate
The states of the FPDP signals (PIO1, PIO2, DIR, and NRDY) are transmitted across the link at
varying rates. The worst-case rate at which these signals are sampled is for CRC checked filled
data frames and the Copy Mode Master bit set . In this case, the signals are sampled every 521
words. For CRC checked filled data frames and the Copy Mode Master bit clear, these signals
are sampled every 518 words. Table 6-3 summarizes the worst-case sampling frequencies for the
different link transmission speeds (SL240).
Table 6-3 Sampling Frequencies
With CRC and
Copy Mode
Master bit = 0
Without CRC
and Copy Mode
Master bit = 0
With CRC and
Copy Mode
Master bit = 1
Without CRC and
Copy Mode
Master bit = 1
NOTE: The Copy Master Mode is located in the Link Control register.
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