400ms delay between ATT Write request and response

Hi, 

On a nrf52840 running SDK 17.0.2 and Softdevice 7.2, while being connected to two devices in central and peripheral role, I observe that on the connection 
where the nrf is in peripheral role, a whopping 400ms delay between an ATT write request and its response (detected and measured with wireshark)

In the Message sequence diagram "GATTS write request without authorization"  I get the impression that the response is sent "immediately"  by the softdefice,
where that immediately intuitively is in the 20ms range rather than 400ms..

My questions are:

- What influences the observed delay (I suspect connection parameters a bit..)

- Can I have influence on this in such way that the delay is reduced?

I can see that if I disconnect the peer in peripheral role (where the nrf is central) the delay drops to some 20-50ms.

Thank you, jmr.

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  • Hi 

    It would definitely be interesting to know the connection parameters used, both for the central and peripheral connection. 

    Is the SoftDevice also advertising or scanning while the two connections are active?

    When the SoftDevice has multiple connections ongoing there will be occasional conflicts between links, in which case one of the links will skip a connection event in a round robin scheme where the different connections are prioritized in turn. 

    As for the message sequence chart it is interesting to see that the response happens right away. Normally any ATT request will have to be handled by the application, which means you will not be able to get the response on the same connection event that you receive the request. 
    I will check with the SoftDevice team tomorrow and get a clarification on how this works. 

    Best regards
    Torbjørn

Reply
  • Hi 

    It would definitely be interesting to know the connection parameters used, both for the central and peripheral connection. 

    Is the SoftDevice also advertising or scanning while the two connections are active?

    When the SoftDevice has multiple connections ongoing there will be occasional conflicts between links, in which case one of the links will skip a connection event in a round robin scheme where the different connections are prioritized in turn. 

    As for the message sequence chart it is interesting to see that the response happens right away. Normally any ATT request will have to be handled by the application, which means you will not be able to get the response on the same connection event that you receive the request. 
    I will check with the SoftDevice team tomorrow and get a clarification on how this works. 

    Best regards
    Torbjørn

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