| Information | NOP | Used by each node transmitter to indicate the idle condition, report receiver flow control updates, and send other miscellaneous information to its corresponding receiver. These packets are not forwarded by the receiver and no response or data is associated with them. |
| Information | Sync/Error | Sent by each node transmitter during link synchronization or by a device enabled to report errors using the Sync flood mechanism to indicate the need for link reset and re-synchronization. During a Sync flood, each recipient re-issues the Sync packets onto all outgoing links on the chain until reset is detected . There are no response or data packets associated with a Sync packet. |
| Request | Sized Write (Posted) dword or byte transfers OK | A posted sized write is used to initiate a write transfer of dwords or bytes of data to a target. For dword writes , the 1-16 dword data packet immediately follows the write request. For byte writes, a single dword "byte mask" precedes a data packet of 1-8 dwords (containing up to 32 valid bytes). No response is ever returned to a posted write and devices in the target path may deallocate buffers as soon as the request and data are forwarded. |
| Request | Sized Write ( Non-Posted ) dword or byte transfers OK | A non-posted sized write is also used to initiate a write transfer of dwords or bytes of data to a target. For dword writes, the 1-16 dword data packet immediately follows the write request. For byte writes, a single dword "byte mask" precedes a data packet of 1-8 dwords (containing up to 32 valid bytes). The Target Done response will be sent when the write completes (either by the target or by an EOC device). Bridges in the target path must track outstanding non-posted write requests until the target done response is returned. |
| Request | Broadcast Message | Broadcast messages originate at the host bridge, and are accepted and propagated downstream on all links by each device which sees them. As they are posted requests, there is no response and devices in the target path may deallocate buffers as soon as the broadcast message request is forwarded. |
| Request | Sized Read dword or byte transfers OK | A sized read is used to initiate a read transfer of dwords or bytes from a target. For byte reads, a single dword of data is returned immediately after the read response. For dword reads, 1-16 dwords are returned immediately after the read response. Bridges in the target path must track all outstanding read requests until the read response and data are returned. |
| Request | Flush | Issued by a requester to force its preceding posted writes in the same transaction stream to the Host Bridge. This is a non-posted request and the Host Bridge returns a Target Done Response when the flush of all previous posted writes for this source is completed to memory (or to the destination chain in a peer-to-peer transaction). Bridges in the target path must track outstanding Flush requests until the Target Done Response is returned. There is no data packet associated with the Flush. |
| Request | Fence | Issued to force the host bridge to place a barrier between previous and subsequent posted writes in all transaction streams. The Host Bridge will push previous writes for all streams to memory before allowing any subsequent posted writes with( PassPW clear) to be processed . Unlike Flush, this command is posted. There will be no response; devices in the target path may deallocate buffers as soon as Fence request is forwarded. There is no data packet associated with the Fence. |
| Request | Atomic RMW | Issued by a requester seeking to perform a read-modify-write of a memory location in a single transaction. This hybrid request causes a transaction made up of a non-posted write operation followed by a read response with data. There are two variants of Atomic RMW (Fetch & Add and Compare & Swap.) Because Atomic RMW requests are always non-posted, bridges in the path must track outstanding Atomic RMW requests until the response/data are returned. |
| Response | Read Response | Issued by a target when it is ready to either return previously requested read data (see Sized Read and Atomic RMW requests) or an error indication that the request did not complete properly. The read response immediately precedes read data being returned by the target. If an error occurred, the requested amount of data is returned anyway; response error bits will indicate that it is not valid and whether the response was sourced by the original target or an end-of-chain device. |
| Response | Target Done Response | Issued by a target to confirm the completion of an earlier non-posted write or Flush request. There is no data packet associated with a Target Done response. If an error occurred in completing the original request, the target done response error bits indicate the failure and whether it occurred at the original target or the request was inadvertently sent to an end-of-chain device. |
