220.127.116.11. Initial Lane Synchronization
The receivers in Subclass 1 and Subclass 2 modes store data in a memory buffer (Subclass 0 mode does not store data in the buffer but immediately releases them on the frame boundary as soon as the latest lane arrives.). The RX IP core detects the start of multiframe of user data per lane and then wait for the latest lane data to arrive. The latest data is reported as RBD count (csr_rbd_count) value which you can read from the status register. This is the earliest release opportunity of the data from the deskew FIFO (referred to as RBD offset).
The JESD204B RX IP core supports RBD release at 0 offset and also provides programmable offset through RBD count. By default, the RBD release can be programmed through the csr_rbd_offset to release at the LMFC boundary. If you want to implement an early release mechanism, program it in the csr_rbd_offset register. The csr_rbd_offset and csr_rbd_count is a counter based on the link clock boundary (not frame clock boundary). Therefore, the RBD release opportunity is at every four octets.