2.1.7. Deskew Logic
When multiple streams are bonded together, the skew between multiple EMIB interfaces must be removed. The F-tile PMA Direct and FEC Direct IPs automatically compensate for the skew between multiple EMIB interfaces without the need for intervention.
TX Deskew Logic
Once bonding is enabled, deskew logic in the transmit direction aligns the EMIB interface by generating internal deskew pulses every 16 or 32 clock cycles (depending on variant configuration) for all TX EMIB interfaces. These pulses are used to align the transmit parallel data before insertion into the PMA. This logic is generated for all IP modes.
RX Deskew Logic
Once bonding is enabled, optional deskew logic in the receive direction aligns the EMIB interface based on deskew pulses received in the RX data. In PMA Direct mode, this optional RX deskew is implemented for PAM4 mode when the number of EMIB interfaces per PMA is greater than one. In PMA Direct mode, the deskew logic operates on EMIB interfaces associated with each PMA independently. For example, for a 2-lane PMA Direct variant, the deskew logic deskews the EMIB interfaces for Lane 1 independently from the EMIB interfaces for Lane 2. In FEC Direct mode, this optional RX deskew is implemented when the total number of EMIB interfaces is greater than one. In FEC Direct Mode, the RX deskew logic aligns all the EMIB interfaces together. For example, for a 2-lane FEC Direct variant, the deskew logic deskews the EMIB interfaces for Lane 1 together with the EMIB interfaces from Lane 2. Whenever RX deskew is enabled, all rx_coreclkin inputs are expected to be driven by the same source. The RX Deskew logic can deskew up to five rx_coreclkin cycles.
When operating in NRZ mode with no RS-FEC, deskew logic is always disabled.
In the RX direction, when operating in either PAM4 mode or FEC Direct Mode, deskew logic can be turned on with Enable RX de-skew when available parameter in the IP parameter editor. If the current configuration does not support RX de-skew, the parameter editor displays an information message during generating indicating that RX deskew is not supported for the current configuration.
When the deskew logic is disabled, you must deskew the rx_parallel_data buses coming out of each EMIB based on the RX deskew pulses provided by the IP. These deskew pulses appear on rx_parallel_data when the PMA is in double data width mode and rx_parallel_data when the PMA is in single width mode.
The following figure shows sample behavior on rx_parallel_data in single width mode before and after re-alignment.