The following register-to-register delays must be accounted for in the cable delay calculation.
• One datapath clock cycle for the cycle that clocks the transmit data into the transceiver.
• In cores supporting line rates above 4,915.2 Mb/s and in all Artix-7 FPGA based cores, one datapath clock cycle to clock the data through the transmit multiplexer. In cores supporting 10,137.6 Mb/s and higher an extra datapath clock cycle is added for the delay through the scrambler.
• One recovered clock cycle (Artix-7 devices) or one datapath clock cycle (UltraScale architecture, Zynq-7000 SoC, Virtex-7, and Kintex-7 devices) for the delay from the output of the transceiver into the CDC FIFO. In cores supporting line rates above 4,915.2 Mb/s, there is one extra datapath clock cycle, or recovered clock cycle in Artix-7 devices, to clock the data out of the transceiver.
• One datapath clock cycle for clocking the data out of the CDC FIFO.
• In cores supporting line rates above 4,915.2 Mb/s, one datapath clock cycle, or recovered clock cycle in Artix-7 devices, for clocking the data through the descrambler.
• Two datapath clock cycles for delay in the control path of the R21 coarse timer.
• (Artix-7 devices only.) One recovered clock cycle for delay in converting from 2 bytes to 4 bytes.
• (12,165.12 and 10,137.6 Mb/s capable cores implemented on Zynq-7000 SoC, Kintex-7, and Virtex-7 devices only.) Two datapath clock cycles to clock the data in and out of the transmit CDC FIFO.
This leads to the additional delays described in the following subsections.