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Summary

Samsung S8 when connected via bluetooth will randomly open an HFP SCO connection without initiating or receiving a mobile call.

Bug Description - User Story

I listen to music with Bluetooth headphones (Sony SBH60) all through my workday, and my phone will automatically connect to my car's media headkit (Kia Cee'd) when I am driving for handsfree phone calls.

I first noticed the problem just over two weeks ago.

When listening to music with my headphones, I would hear a 'click', the music would become flatter and external sounds would be louder sometimes. At first I thought the music codec used by A2DP was changing. After a while, there would be another click and the music quality would improve again.

When in my car, I listen to the radio but my phone is connected for handsfree (HFP/HSP). I noticed the radio would cut out and the head unit would display:

Calling...
07564627133

However, my phone's display has NO indication of a mobile originated or mobile terminating call. If I hit the 'call hangup' button control on my steering wheel (AVRCP Bluetooth control), the radio comes back on and the head unit display goes back to the radio station display.

Eventually, I put two and two together. When on my headphones at work I realised that 'click' and strange audio quality is actually mono not stereo. * I am not sure if the headphone mic becomes active or not. * I am not sure if the audio is mono because it is now SCO and not ACL A2DP streaming. When this happens, if I click the 'user action' button on my headphones, it acts like a call hang-up and audio quality is restored.

Again, the phone does not indicate an incoming our outgoing mobile call.

Theory

Some aspect of the HFP Call Setup procedure is occurring on Bluetooth, without a call actually being in place.

Since two different Bluetooth remote devices have exhibited a variant of this HFP behaviour, the issue is with the Samsung S8 gateway not the headset.

Since this behaviour is recent, a recently installed application could be doing this and it may not be the phone or Android that is responsible.

Background

I am an embedded software engineer, I work for Qualcomm on System on Chip Bluetooth Devices and my area of speciality is Bluetooth Profiles above HCI. That's lucky... or suspicious.

To be clear, I know about Bluetooth but I don't know much about Android or Bluetooth on Android (Bluedroid). I have messed around with Android, written some simple apps and I know a little about Android Debug Bridge (ADB).

Yes, it has occurred to me that one of my colleagues has done something to my phone as a prank.

I am posting this to see if anyone else has seen this issue, and as an initial investigation bug report.

Next Steps

  1. Look up the phone number.

    Nothing comes up from an internet search

  2. Call the number (UK mobile call).

    'The number you have dialled is not recognised'.

  3. Use a Stereo Headset Dev Kit and Frontline Sniffer to get an airtrace.

  4. Enable developer mode, use ADB to get the BTSnoop log from the phone.

  • This is a bug that appeared a couple of weeks ago. There is an open issue on the issue tracker. You can star it to be kept informed of any updates. (but please don't comment unless you have something useful to add, it just spams people with emails). Although the bug says it is with Android 8 (Oreo) there are reports of the same issue on previous versions of Android too. – bmdixon Oct 30 '17 at 10:13
  • Thanks, I looked but didn't find anything but I was probably using the wrong terms. – Simon Peverett Oct 30 '17 at 21:06

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