The following figure illustrates the signals associated with the completer completion interface of the core. The core delivers each TLP on this interface as an AXI4-Stream packet. The packet starts with a 96-bit descriptor, followed by data in the case of Completions with a payload.
The completer request interface supports two distinct data alignment modes, selected during core customization in the AMD Vivado™ IDE. In the Dword-aligned mode, the first byte of valid data must be presented on lane n = (S + 12 + (A mod 4)) mod 64, where A is the byte-level starting address of the data block being transferred and S is the lane number where the first byte of the descriptor appears. The address A is taken as the value in the Lower Address field of the descriptor. The starting lane number S is always 0 when the straddle option is not used, but can be 0 or 32 when straddle is enabled.
In the 128-bit address-aligned mode, the lane number corresponding to the first byte of the payload is determined as n = (S + 16 + (A mod 16)) mod 64, where S is the lane number where the first byte of the descriptor appears (which can be 0 or 32) and A is the address corresponding to the first byte of the payload. Any gap between the end of the descriptor and the start of the first byte of the payload is filled with null bytes.
The interface also supports a straddle option that allows the transfer of up to two TLPs in the same beat across the interface. The straddle option can be used only with the Dword-aligned mode, and is not supported when using the 128-bit address aligned mode. The descriptions in the sections below assume a single TLP per beat. The operation of the interface with the straddle option enabled is described in Straddle Option on CC Interface.