The Interlaken Protocol does not restrict the use of the calendar entries to a particular flow control implementation. As such, you can decide if one or more of the calendar entries should be designated to control the flow control of the entire interface (that is, link level flow control). For example, if the calendar length is 32, calendar slots 0 and 16 can be selected as link level flow control bits. This transmits the link level information with every burst control word.
The Interlaken 600G IP core implements the in-band flow control mechanism as described in the Interlaken Protocol Definition, Revision 1.2. The Interlaken 600G IP core is configured to have a fixed calendar length. You must connect the link level flow control information to the appropriate input pins of the RX interface and interpret the appropriate output pins of the TX interface.