
C–2 Appendix C: Optimum Frequency for rxsys_clk
POS-PHY Level 4 IP Core User Guide December 2014 Altera Corporation
If you increase the LVDS data rate to 820 Mbps (
rdint_clk
=
rsclk
= 102.5 MHz), the
new minimum required
rxsys_clk
frequency from restriction (a) is:
(4/3.125) × 102.5 = 131.2 MHz
and from restriction (b) is:
102.5 × 4/3 = 136.667 MHz
If you do not want to increase the
rxsys_clk
frequency, you can increase the status
frame length. By setting the calendar multiple to 2, the required frequency from
restriction (b) is
Status frame length = 4
rxsys_clk
frequency 102.5 × 5/4 = 128.125 MHz
By changing the calendar multiple to 2, the required minimum
rxsys_clk
frequency
is 131.2 MHz (from restriction (a)).
Figure C–1. Minimum Frequency Ratio versus Packet Size
Ratio
Packet Size
(Bytes)
0.8
MegaCore Width = 64
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
20 30 40 50 60 70 80 90 100 110
MegaCore Width = 128
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