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Debian and 2.6 kernel: Touchpad sync problem - solution

Posted by rmcgowan on Wed 22 Mar 2006 at 09:20

This began as a presumed problem with Debian, since the issue showed up when I upgraded from kernel 2.4.x to 2.6.x, resulting in total loss of functionality of my externally connected PS2 mouse. The Synaptic Touchpad on my Dell Latitude continued to work, however.

I assumed there was a problem of some sort with the kernel itself or the PS2 mouse driver, so I downloaded the latest kernel from www.kernel.org, compiled and installed, but no dice, the external mouse still failed to work.

But this failure affected the Touchpad, this time, and X failed to start. This was good luck for me, as it put me in the vt01 console, where I finally saw the errors being generated when I used the external mouse.

So, lesson 1: When something doesn't work, CHECK the log files and/or dmesg output!

The specific error message was:

psmouse.c: TouchPad at isa0060/serio2/input0 lost sync at byte 1

This error was generated multiple times (10-30 or more) as I moved the external mouse. When I used the Touchpad, a message from the same driver indicated it had 're-synced', and gpm took the input and displayed its selection cursor, as expected.

Step two, and lesson two, is to search the web for reports of the error, which I did. Which leads to lesson three: the web is a cool tool and can be useful, but getting to the useful data can be a real time sink, so be prepared.

The result of my search came back with literally thousands of matches, of which nearly all were either reports of the problem, or discussions about it but with no viable solutions.

It took nearly 4 hours before luck and persistence (to say nothing of modified search criteria) got me to a note from a developer familiar with the Synaptic Touchpad, which explained both why the problem exists and how to fix it.

The problem has to do with the 'non standard' output of the touchpad, so far as mice are concerned. This is apparently needed to support special features, like double or triple tapping, sliding and so on, used to emulate various button clicks and mouse movement.

Bottom line is that the Touchpad produces more bytes per event than the mouse does, so when the mouse input is read, it is automatically "out of sync" as compared to the Touchpad.

The solution is simple: force the Touchpad to work as a generic PS2 mouse, without any support for the special features. This is accomplished by setting a boot parameter:

psmouse.proto=imps

The author of the email I found suggested using either 'imps' or 'bare', but I'd think that any of the PS2 mouse definitions as presented during Xserver setup would work, so long as the two selections match (not tested, however).

Since I use grub as my bootloader, I added this boot parameter after the 'ro' on the 'kernel' line:

kernel /boot/vmlinuz-2.6.15.6 root=/dev/sda1 ro psmouse.proto=imps 

I would guess that the reason the external mouse worked in the 2.4.x kernel is that it does not have a specific Touchpad driver, or if it does, it doesn't support anything other than a generic PS2 interface, and so it works when an external mouse is connected.

And, of course, this is all irrelevant, if you really want to have the full Touchpad functionality. In which case, you'd have to give up the external mouse.

 

 


Re: Debian and 2.6 kernel: Touchpad sync problem - solution
Posted by Anonymous (83.17.xx.xx) on Wed 22 Mar 2006 at 21:09
It took nearly 4 hours before luck and persistence (to say nothing of modified search criteria) got me to a note from a developer familiar with the Synaptic Touchpad, which explained both why the problem exists
Can you provide the link?

Thanks in advance.

[ Parent ]

Re: Debian and 2.6 kernel: Touchpad sync problem - solution
Posted by rmcgowan (143.127.xx.xx) on Fri 24 Mar 2006 at 18:54

Maybe...;)

It seems I was playing around with some of the Firefox security stuff and I turned on the 'Clear Private Data' tool to clean things out on exit. So, I have no history for the exact page involved and though I tried, a quick search back hasn't found the exact page.

But, I did find a similar thread which you can access at:

http://www.uwsg.iu.edu/hypermail/linux/kernel/0406.3/0032.html

This article is listed in this index first, but it's clearly somewhere inside a much longer thread. It does, however, mention the psmouse.prot variable and the two values I mentioned.

NOTE!! One thing this indicates, which was not mentioned in the the email I originally found, is that the values supplied to this variable may not necessarily match what is listed for mouse protocols when setting up XWindows. In fact, the content of this email seems to imply that the 'imps' value is a way to tell the Touchpad to turn off the special features, rather than a way to tell a device to support a particular minimal feature set. Put another way, this may be specific to the Synaptics Touchpad driver.

So, the comment in my original post about maybe being able to use the mouse names listed by XWindows for PS2 mice is wrong.

[ Parent ]

Re: Debian and 2.6 kernel: Touchpad sync problem - solution
Posted by Anonymous (213.58.xx.xx) on Sat 23 Sep 2006 at 23:40
Well the cool thing would be to know what's causing the problem and to fix it.
One thing that I like is the scrooling button that my touchpad has. That goes away if I don't use the synaptics driver. Anyway, it still does the same with all protocols I've tried.
I've installed kernel 2.16.18 and I have the same problem.
Good luck!
TonyPower

[ Parent ]

Re: Debian and 2.6 kernel: Touchpad sync problem - solution
Posted by Anonymous (84.121.xx.xx) on Tue 21 Nov 2006 at 22:26
I LOVE YOU! Grasias!

[ Parent ]

Re: Debian and 2.6 kernel: Touchpad sync problem - solution
Posted by Anonymous (84.56.xx.xx) on Sun 11 Feb 2007 at 22:31
Thank you very much. Your post has fixed the one of the worst problems I ever ran into.

Philipp

[ Parent ]

Re: Debian and 2.6 kernel: Touchpad sync problem - solution
Posted by Anonymous (200.213.xx.xx) on Tue 11 Sep 2007 at 17:16
thss!! .. I had the same problem ..

.

[ Parent ]

Re: Debian and 2.6 kernel: Touchpad sync problem - solution
Posted by Anonymous (69.165.xx.xx) on Sat 27 Feb 2010 at 19:34
How to get full Touchpad functionality and to use the same time usb connected mouse?

[ Parent ]