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Question about CHI spec

Jinyu Dong

In CHI.G Chapter B2.9.2.1 metioned that "The AllowRetry field must be asserted the first time a transaction is sent.",

but in AMBA CHI C2C spec B4,1,2 said the Request Retry flow dose not support in C2C,and AllowRetry field can not be transfer.

So is seems mismacth between two Spec, so when AllowRetry bit is after the C2C to the remote die is 0, and not satisyied the CHI spec"The AllowRetry field must be asserted the first time a transaction is sent."

Is it acceptable and any risk?

I'm looking forward to your replay.

Thanks a lot!

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  • +1 Arm Employee Badge in reply to Jinyu Dong

    Hi Jinyu,

    1. The gateway logic is ultimately what is used to convert between on-chip CHI, to packed CXS. Ultimately, it is the logic that implements the Protocol to Link Layer mapping, when viewed in reference to Figure B2.1: C2C interface structure in CHI C2C-A. This would be part of any interconnect IP, including CMN, that would then output CXS towards the Link Layer.

    2 Yes, that is correct. A RetryAck message must not be sent across the C2C interface, so if the HN provides one, the C2C Rx gateway must buffer the request until PCrdGrant and then re-issue.

    Hope this helps.

    Ben

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  • +1 Arm Employee Badge in reply to Jinyu Dong

    Hi Jinyu,

    1. The gateway logic is ultimately what is used to convert between on-chip CHI, to packed CXS. Ultimately, it is the logic that implements the Protocol to Link Layer mapping, when viewed in reference to Figure B2.1: C2C interface structure in CHI C2C-A. This would be part of any interconnect IP, including CMN, that would then output CXS towards the Link Layer.

    2 Yes, that is correct. A RetryAck message must not be sent across the C2C interface, so if the HN provides one, the C2C Rx gateway must buffer the request until PCrdGrant and then re-issue.

    Hope this helps.

    Ben

Children
  • 0 in reply to Ben Hicks

    Hi Ben,

    Since "The AllowRetry field must be asserted the first time a transaction is sent" has been mentioned in CHI.G spec, is that acceptable for all the Node in CHI Bus Architecture just disable the "Transaction Retry mechanism", and keep the "AllowRetry" always low for all kind of request transaction. What kind of risk will it lead with.

    Looking forward to your reply with best regard :)

    Thanks

  • 0 Arm Employee Badge in reply to Lingfan Tang

    Hi Lingfan,

    Not adhering to the AllowRetry rules for the first time a transaction is sent would be a protocol violation, and would very likely cause behavioral issues. AllowRetry=0 is often interpreted as a very strict meaning, namely that a PCrdGrant allocated credit is being used. Credit counters are often acted upon by this.

    The option for CHI without Retry is being considered for a future release, but I would expect this to be covered by properties and rules, rather than by changes to protocol field values. This is not something that is currently supported as of CHI-G.

    Hope this helps.

    Ben