The user application sends completion data for a completer request to the completer completion interface of the core as an independent AXI4-Stream packet. Each packet starts with a descriptor, and can have payload data following the descriptor. The descriptor is always 12 bytes long, and is sent in the first 12 bytes of the completion packet. The descriptor is always transferred in the first beat of a Completion TLP. When the user application splits the completion data for a request into multiple Split Completions, it must send each Split Completion as a separate AXI4-Stream packet, with its own descriptor.
The format of the completer completion descriptor is illustrated in the following figure. The individual fields of the completer request descriptor are described in the following table.
| Bit Index | Field Name | Description |
|---|---|---|
| 6:0 | Lower Address | For memory read Completions, this field must be set to the least significant 7 bits of the starting byte-level address of the memory block being transferred. For all other Completions, the Lower Address must be set to all zeros. |
| 9:8 | Address Type | This field is defined for Completions of memory transactions and Atomic Operations only. For these Completions, the user logic must copy the AT bits from the corresponding request descriptor into this field. This field must be set to 0 for all other Completions. |
| 28:16 | Byte Count |
These 13 bits can have values in the range of 0 – 4,096 bytes. If a Memory Read Request is completed using a single Completion, the Byte Count value indicates Payload size in bytes. This field must be set to 4 for I/O read Completions and I/O write Completions. The byte count must be set to 1 while sending a Completion for a zero-length memory read, and a dummy payload of 1 Dword must follow the descriptor. For each Memory Read Completion, the Byte Count field must indicate the remaining number of bytes required to complete the Request, including the number of bytes returned with the Completion. If a Memory Read Request is completed using multiple Completions, the Byte Count value for each successive Completion is the value indicated by the preceding Completion minus the number of bytes returned with the preceding Completion. |
| 29 | Locked Read Completion | This bit must be set when the Completion is in response to a Locked Read request. It must be set to 0 for all other Completions. |
| 42:32 | Dword Count | These 11 bits indicate the size of the payload of the current packet in Dwords. Its range is 0 – 1K Dwords. This field must be set to 1 for I/O read Completions and 0 for I/O write Completions. The Dword count must be set to 1 while sending a Completion for a zero-length memory read. The Dword count must be set to 0 when sending a UR or CA Completion. In all other cases, the Dword count must correspond to the actual number of Dwords in the payload of the current packet. |
| 45:43 | Completion Status |
These bits must be set based on the type of Completion being sent. The only valid settings are:
|
| 46 | Poisoned Completion | This bit can be used by the user logic to poison the Completion TLP being sent. This bit must be set to 0 for all Completions, except when the user logic has detected an error in the block of data following the descriptor and wants to communicate this information using the Data Poisoning feature of PCI Express. |
| 63:48 | Requester ID | PCI Requester ID associated with the request (copied by the user logic from the request). |
| 71:64 | Tag | PCIe Tag associated with the request (copied by the user logic from the request). |
| 79:72 | Target Function/Device Number |
Device and/or Function number of the Completer Function. Endpoint mode: ARI enabled:
ARI disabled:
Upstream Port for Switch use case (Endpoint mode is selected within the IP): ARI enabled:
ARI disabled:
Root Port mode (Downstream Port): ARI enabled:
ARI disabled:
|
| 87:80 | Completer Bus Number |
Bus number associated with the Completer Function. Endpoint mode:
Root port mode (Downstream Port):
|
| 88 | Completer ID Enable |
1'b1: The client supplies Bus, Device, and Function numbers in the descriptor to be populated as the Completer ID field in the TLP header. 1'b0: IP uses Bus and Device numbers captured from received Configuration requests and the client supplies Function numbers in the descriptor to be populated as the Completer ID field in the TLP header. Endpoint mode:
Upstream Port for Switch use case (Endpoint mode is selected within the IP):
Root Port mode:
|
| 91:89 | Transaction Class (TC) | PCIe Transaction Class (TC) associated with the request. The user logic must copy this value from the TC field of the associated request descriptor. |
| 94:92 | Attributes | PCIe attributes associated with the request (copied from the request). Bit 92 is the No Snoop bit, bit 93 is the Relaxed Ordering bit, and bit 94 is the ID-Based Ordering bit. |
| 95 | Reserved | Reserved for future use. |