Capturing BLE Scan Parameters

Question

Anviori OP

Created Dec ’23

Replies 1

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Hello,

I've been trying to debug a Bluetooth issue with an app I'm working with. Is there a way to capture the LE Set Scan Parameters HCI event?

I've downloaded the Bluetooth debug profile and managed to capture the HCI traffic using the Packet Logger tool. The problem is that I don't see the Scan Parameters event occurring. I can see Advertisement parameters being set (which is odd that the iPhone is doing so, even with Airdrop and BLE disabled).

I can see lots of Advertising Reports which indicate that the device is scanning; but I can never catch when the parameters are set for that.

I've attached a sample log of me just toggling the Bluetooth off and on. Any insight is appreciated.

Thank you

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Answer 1

DTS Engineer OP

Apple

Dec ’23

Scan parameters are internally controlled by the system and change dynamically based on the app and device state. The actual numbers for scan parameters are undocumented implementation detail.

There is, though, a set of recommended advertising intervals that is known to minimize the discovery time for the scan parameters the device will be using. It is recommended that peripherals advertise at 20ms interval as long as it is able to, and at least for 30 seconds, and if it has not been discovered then, drop to one of the following longer intervals: 152.5 ms, 211.25 ms, 318.75 ms, 417.5 ms, 546.25 ms, 760 ms, 852.5 ms, 1022.5 ms, 1285 ms

These exact intervals will give you the optimum discovery time for power, in the general range of advertising interval you are able to use.

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