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Slow DFU speed

Hello,

yesterday I got a Thingy:52 device at an event held in Frankfurt/Germany. At home I've tested the DFU for the latest firmware and observed that the image was transfered at a very low speed. The image was transfered with 0.4 kByte/second. I've the BLE packets logged at the smartphone and found the following:

  1. In the LE Connection Complete Event I've seen that the connection interval was set to 48.75ms.
  2. Later the Thingy (peripherial) sends the Connection Parameter Update Request with connection interval set to 15ms-30ms. The smartphone (central) accepts this request by sending Connection Parameter Update Response.
  3. After that the complete firmware will be transmitted packet by packet in the connection interval. But only one 20 byte packet in one connection interval. And the interval is 40-50ms in reality.

That results in 45ms/20bytes or 0.4 kByte/second transfer speed. Why do I have so low transfer speed?

The smartphone is a Samsung Galaxy S4 mini (GT-I9195).

Thanks in advance

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