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  • Case ID: 120678
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Slave latency & communication speed Nordic's trick?

Valer_I

Hello, I use nRF51822 based device with s110 softdevice. I noticed that data exchange is different on different connected centrals. For test I used Windows and Android powered central. The task is to send request and receive responce in notification from the device. After connection I request similar connection parameters (conn interval 30ms, slave latency 16) and they are accepted by both centrals. The speed results are different. Data exchange with windows is about 10 times faster than with Android. After sniffing I noticed that softdevice send Empty PDU after each notification packet and then enables slave latency functionality (i.e. skipping n central's packets). Windows driver in some way send next write request just after notification sent. And communication is very fast, like with slave latency = 0. In case of Android the driver send Empty PDU after notification from peripheral and than write request, but soft device do not react for it fot slave latency number times. Windows:

M->S  Write Command  (request1)
S->M  Empty PDU
M->S  Empty PDU
S->M  Notification  (responce1)
M->S  Write Command  (request2)      !!!
S->M  Empty PDU
M->S  Empty PDU
S->M  Notification  (responce2)

Android:

M->S  Write Command  (request1)
S->M  Empty PDU
M->S  Empty PDU
S->M  Notification  (responce1)
M->S  Empty PDU     <- This makes data exchange slow 
S->M  Empty PDU
M->S  Write Command  (request2)      !!!
M->S  Write Command  (request2)
M->S  Write Command  (request2)
...
M->S  Write Command  (request2)
S->M  Empty PDU
M->S  Empty PDU
S->M  Notification  (responce2)

I feel the softdevice has some pause after sending the packet before enabling slave latency function. Am I right? If yes what exact pause time is?

Thanks

UPDATED:

Android: from line 730 ANDROID_CAP

Windows: from line 851 WINDOWS_CAP

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  • 0

    I don't think there is any kind of "answers" from the softdevice to write command. Unless that what you programmed your program on the chip to do.

    It should be noted that on the Windows' case Slave latency was not used.

    If you actively queue the notification, the softdevice won't enter slave latency mode but wake up and will wake up in the next connection event and send the packet instead.

    We need to have a look at how and when you send the notification. Please provide your code.

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  • 0

    I don't think there is any kind of "answers" from the softdevice to write command. Unless that what you programmed your program on the chip to do.

    It should be noted that on the Windows' case Slave latency was not used.

    If you actively queue the notification, the softdevice won't enter slave latency mode but wake up and will wake up in the next connection event and send the packet instead.

    We need to have a look at how and when you send the notification. Please provide your code.

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