# Ubuntu – How to debug lag using Bluetooth connected mouse and A2DP headset

12.04a2dpbluetoothinput-devices

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.

• 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 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?

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.