Rejecting Packets


Once system initialization is complete, packet rejection should be a rare event. The only non-error rejection after initialization would be the arrival of a broadcast message which is intended to travel to the end of the chain and then be dropped by the end-of-chain device. Prior to the completion of system initialization, other devices may have not completed link initialization ( Link Initialization bit is clear). If they have not been programmed to hold incoming packets pending completion of initialization ( Drop on Uninitialized Link bit is set), they will behave as an end-of-chain device and reject packets temporarily.

Actions taken when a packet is rejected by an end-of-chain device, or by an interior device which has not completed initialization and is behaving temporarily as one, depends on the type of packet.

Rules For Rejection

  1. Broadcast requests which have completed the trip to the end of a chain are silently dropped. These are always posted, so no response is expected or sent.

  2. Non-posted downstream directed requests (UnitID = 0) cause the return of a Target Done response (for non-posted writes or Flush) or a Data Response (for reads or Atomic RMW). The response for rejected non-posted downstream requests will have the Error and NXA error bits set, and the bridge bit clear. The UnitID field will be set to either 0 or that of the end-of-chain device. Read responses are accompanied by all requested data (driven to value of FFh)

  3. Non-Posted upstream directed requests ( non-zero UnitID) cause the return of a Target Done response (for non-posted writes or Flush) or a Data Response (for reads or Atomic RMW). The response for rejected non-posted upstream requests will have the Error and NXA error bits set, and the bridge bit set. The UnitID field must be set to that of the original requester (without its UnitID and the bridge bit set in the response, an interior node won't accept the response). Read responses are accompanied by all requested data (driven to value of FFh)

  4. Rejected response and posted request packets are dropped.



HyperTransport System Architecture
HyperTransportв„ў System Architecture
ISBN: 0321168453
EAN: 2147483647
Year: 2003
Pages: 182

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