Dual clock mode is introduced in link layer to support different
datapath widths on the transport layer than on physical layer.
- Link clock : lane rate / 40 for input datapath width of 4 octets 8b10b
- Device clock : Link clock * input data path width / output datapath width
Supports four clock configurations, single or dual clock mode with or
without external device clock.
The configuration interface reflects the dual clock domain.
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