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gertvdijk
Asked: 2012-09-18 03:30:10 +0800 CST

How to debug lag using Bluetooth connected mouse and A2DP headset?

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I own a Logitech M555b mouse for use with my HP Elitebook 8570w laptop running Kubuntu 12.04. Works fine right after connecting using the KDE Bluetooth control module.

However, after some time (seemingly random), it starts to lag. Movements are being delayed for roughly 500ms for a short period of time. Usually it recovers after some time too, but it can take minutes. All actions are being delayed: movements, click, scrolls. Additionally, the movements can be choppy during these times.

A workaround that always works for the same short period of time is to disconnect an re-connect the mouse. This can be done using the same KDE Bluetooth control module.

What did I try already?

  • Running this at boot time:

    echo on > `readlink -f /sys/class/bluetooth/hci0`/../../../power/level

    To disable any power saving features on the Bluetooth hci0 device.

  • Check the mouse's batteries (it's just a week old, other new batteries: same result)

  • Checking logs and kernel messages about Bluetooth-related entries: none aside the expected messages on connect time.
  • I'm running kernel 3.5.0-13-generic as provided in the xorg-edgers PPA. Booting the regular 3.2 Precise kernel results in the same behaviour.

Some other information that may help:

  • It happens when no other Bluetooth connections are active on the machine.
  • Similar symptoms also occur on my Bluetooth stereo (A2DP) headset, but then it's audio lagging and skipping. Swapping Bluetooth profiles as described here then helps. Conclusion: it's not the mouse that's faulty.
  • The headset always worked fine using my now dead Thinkpad T61p with built-in Bluetooth.

  • The bluetooth module in my laptop is connected via USB and shows up as

    0a5c:21e1 Broadcom Corp.

  • Turning the built-in Bluetooth adapter off and using another one works fine, without lag.

    0a5c:2046 Broadcom Corp. Bluetooth Device

I'm mobile and several people around me are using Bluetooth at work (A2DP mostly). It also occurs at home, where my neighbours are probably using Bluetooth as well. It could just be radio interference, but I think Bluetooth connections should just hop to another channel. And, moreover, it just works properly instantly when re-connecting.

Therefore I think it's a software driver issue and I'd like to debug it. Is there any way to get more verbose logging on the Bluetooth(-hid) modules?

12.04

2 Answers

  1. Best Answer

    You could try using the hcidump utility from the package bluez-hcidump to monitor your bluetooth devices and gain in-depth information:

    sudo apt-get install bluez-hcidump

    In the package description, it is noted that:

    The hcidump utility allows the monitoring of Bluetooth activity. It provides a disassembly of the Bluetooth traffic and can display packets from higher level protocols such as RFCOMM, SDP and BNEP.

    You can use the utility to log the output from your device to screen or file; where hciX is your own bluetooth device (hci0 is the default and used if you don't specify anything with -i), you can run:

    sudo hcidump -x -i hciX

    You can save the dump to file by appending to the command -w ~/output, and if you specifically want to know about the audio data you can use the -A switch and thereby extract SCO audio data, although in this case you must always specify an output file:

    sudo hcidump -x -A -i hciX -w ~/output

    You can view a saved dump file by using 

    sudo hcidump -r ~/output

    There are a lot more specific options that you might want to investigate; you can filter by packet type if you want, as by default all packets are dumped. Please see man hcidump or the Ubuntu manpages online for more information.

    The only other option is to install wireshark and see if it can detect your devices; if it can, it will be able to analyse usb and bluetooth traffic, as noted here, but hcidump should give better results.

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  2. I've had some luck using USB tracing to solve strange audio problems. Sometimes you can determine something from the content, or the timing of packets. In my case it was an occasional change in the packet length corresponding to noise I was hearing.

    Here's a page from Wireshark that provides some information.

    You can get a trace simply by doing the following:

    1. sudo modprobe usmon
    2. cd /sys/kernel/debug/usb/usbmon
    3. sudo cat 0u | tee ~/myusbtrace > /dev/null
    4. run your test
    5. kill the process from step 3

    Here is information from the linux project about this, including how to narrow down what you are tracing.

    The second column appears to contain the time, so you should keep a careful watch on how it increments. If it starts smooth and later gets jumpy the problem may be in the bluetooth section.

    If the trace shows irregular packets when there is a problem that could be either USB or bluetooth, but the direction of the irregular packets may indicate whether it is the kernel or driver rather than something on the other side of the USB bus.

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