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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 RQ Interface
Requester Request Descriptor Formats
The user application must transfer each request to be transmitted on the link to the requester
request interface of the core as an independent AXI4-Stream packet. Each packet must start with
a descriptor, and can have payload data following the descriptor. The descriptor is always 16
bytes long, and must be sent in the first 16 bytes of the request packet. The descriptor is
transferred during the first two beats on a 64-bit interface, and in the first beat on a 128-bit or
256-bit interface. The formats of the descriptor for different request types are illustrated in the
following figures.
The format of the following figure applies when the request TLP being transferred is a memory
read/write request, an I/O read/write request, or an Atomic Operation request.
Chapter 4: Designing with the Core
PG346 (v3.3) November 16, 2022
CPM Mode for PCI Express
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