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TMS320C6678: RETRY/ERROR/DONE response when receiving SRIO DoorBell packet

Naoki Kawada
Guru 19890 points
Part Number: TMS320C6678

Hi,

My customer want to clarify about the responses back to SRIO linked pair when C6678 is receiving DoorBell packets.

C6678 SRIO defines the following responses for incoming DoorBell request:
- DONE response, this is typical response
- ERROR, this indicates error response 
- RETRY, the packet is not accepted, so SRIO asks linked pair to send the packet again

My customer wants to know if C6678 SRIO IP generates the above responses *automatically*, or, SW is responsible to initiate the response intentionally. Could you please comment ? Also, what is the condition to generate ERROR and RETRY responses in C6678 SRIO IP ? I could not find the related statement in SRIO UG.

Best Regards,
NK

  • 0
    TI__Guru 65405 points
    The team is notified. They will post their feedback directly here.

    BR
    Tsvetolin Shulev
  • 0 in reply to Cvetolin Shulev-XID
    TI__Mastermind 43296 points
    Hi Naoki,

    The DONE, ERROR and RETRY responses are the control symbols of Packet-accepted, Packet-not-accepted and Packet-retry initiated by SRIO IP. You can find the details including the "condition to generate ERROR and RETRY responses" in Chapter 4 Control Symbol Formats, from RapidIO™ Interconnect Specification, Part 4: Physical Layer 8/16 LP-LVDS Specification (part4.pdf - www.rapidio.org/.../ 6XN Gen2)

    Regards,
    Garret
  • 0 in reply to Garrett Ding
    Guru 19890 points

    Hi Garret,

    Thanks for responding on this. Now the customer wants to know the exact reason why SRIO IP could return RETRY responses. From my understanding, MAU handles incoming DoorBell packets to generate interrupts on local cores. The all incoming packets would be pushed into RX FIFO at first and MAU pops some if those types are regarded as DoorBell. Could you take a look at the following picture ? This is a snippet from SRIO User Guide:

    Because RETRY response seems to be automatically handled by SRIO IP on C6678 (In other words, these are handled before generating interrupts), I`m wondering the main reason would be RX FIFO is full for replying RETRY response. Is my understanding correct ?

    Best Regards,
    NK

  • 0 in reply to Naoki Kawada
    Guru 19890 points
    Hi,

    Do you have any response on this ?

    Best Regards,
    NK
  • 0 in reply to Naoki Kawada
    Guru 19890 points

    Sorry to push you, but my customer is waiting for your reply. Thank you in advance.

    Best Regards,
    NK

  • 0 in reply to Naoki Kawada
    TI__Mastermind 43296 points

    NK,

    Sorry for the late response. I was traveling for Embedded World last week.

    Yes, your understanding is correct. From the SRIO Spec:

    4.2.2 Packet-Retry Control Symbol

    A packet-retry acknowledgment control symbol indicates that the adjacent device in

    the interconnect fabric was not able to accept the packet due to some temporary

    resource conflict such as insufficient buffering and the source should retransmit the

    packet

    Regards, Garrett