Achronix Speedster22i PCIe - Manual (Page 23)

UG030, April 26, 2013 23
Receive Interface
The Receive Interface is the mechanism with which the user receives PCIe
packets from the PCIe bus. Packets are received and presented on the
interface in the same format defined in the PCI Express Specification; the
user receives complete Transaction Layer packets comprised of packet
header, data payload, and optional TLP Digest. The core automatically
checks packets for errors, requests replay of packets as required, and strips
the Physical Layer framing and Data Link Layer sequence number, and Link
CRC (LCRC) before presenting the packet to the user.
The core decodes received TLPs and provides useful transaction attributes
such that the packet can be directed to the appropriate destination without
the need for the user to parse the packet until its destination. If the packet is
an I/O or Memory write or read request, the base address register resource
that was hit is indicated. If the packet is a completion, the packet’s tag field is
provided. The core also provides additional useful transaction attributes.
Packets that appear on the Receive Interface have passed the Sequence
Number, Link CRC, and malformed TLP checks required by the PCI Express
Specification.