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Old 07-01-2017, 01:55 PM   #1
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Registered: Apr 2009
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Raspberry Pi: Using inputattach on Raspbian Jessie


I've been attempting to get a serial trackball working on my Raspberry Pi 2 with inputattach on X Windows under Raspbian Jessie (kernel 4.4.38-v7+). The serial trackball in question is described on the following web page:
Experimenting with a "Tiny Trackball"...
The trackball is connected to the RasPi via the GPIO serial port. I have disabled the default serial console and kernel message logging to the serial port. I have been able to get the trackball working with gpm. The trackball looks like a Microsoft 2-button mouse.

I have not been able to get the trackball working with inputattach, so I can use it under X Windows. I've tried everything I can think of to get it to work without success. While gpm didn't need it, I even enable GPIO pin 17 to output the RTS signal (alternate output 3), in case inputattach needed it to reset the trackball. Even this did not help. I would have thought that the following invocation would work:
inputattach --microsoft /dev/serial0
In my research, I found that the X Windows installation is configured to use libinput (not evdev). The hot-plugging capability precludes the use of the 'traditional' serial mouse driver. Using inputattach appears to me to be the standard approach to using serial pointing devices with libinput.

As a side note, I did write a C++ program to acquire data from the trackball and generate X Window events using libxdo. It works, mostly, but it has its own set of problems. I would prefer to use a common approach, if possible.



Last edited by mcody; 07-01-2017 at 02:02 PM. Reason: Added more information.
Old 07-02-2017, 07:56 PM   #2
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Registered: Apr 2009
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Update on efforts to resolve the issue.

I decided to remove libinput support and install evdev instead:
sudo apt-get remove xserver-xorg-input-libinput
sudo apt-get install xserver-xorg-input-evdev
Then I attempted to use the solution described by RupertPupkin in his post [SOLVED] Configuring a serial mouse on Fedora 19 on the No success. This tells me that it is not an libinput vs. evdev issue.

I also looked into the source code to inputattach, which is part of the linuxconsoletools package, to see how it accesses the serial port. Nothing particularly mysterious. It essentially sets up the serial port to ignore BREAK condition on input, ignore framing errors and parity errors, lower modem control lines after last process closes the device, and ignore modem control lines. Doesn't help me to figure what is going on, though.



hardware, mouse, raspberry pi, serial, xwindows

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