Emulate scrolling in linux (ubuntu) for trackball?

Question

linux

There is a Logitech TrackMan Marble trackball, it has 4 buttons, but there is no scroll, which is somewhat inconvenient. I found on the Internet (and there was also a thread on Habré) how to emulate a scroll: I hold down a small button with my thumb (which by default returns the history in the browser back), and spin the ball, I get a scroll in all directions. If a single press, it works properly. This configuration is the most convenient for me, although there are others (also within the buttons on the trackball). And everything seems to be working, but there is one glitch: often (especially in the browser) this pressing (long) is recognized as a single one (that is, instead of scrolling, it returns back to the history), which is very annoying.
The essence of the question: is it possible to create an emulation of scrolling when a key is pressed on the keyboard (there are a couple of multimedia keys that I do not use, I can bind one of them)? Who realties faced this? Or at least where to dig? You can't find anything like this with a search engine.
Thank you.

Answer 1

Weird, I have the same trackball and the same configuration (thumb button + ball spin). Never failed, I've been using it every day for 2 years.
/etc/X11/xorg.conf

Section "InputClass"
    Identifier      "Marble Mouse"
    MatchProduct    "Logitech USB Trackball"
    MatchIsPointer  "on"
    MatchDevicePath "/dev/input/event*"
    Driver          "evdev"
    Option          "SendCoreEvents" "true"

    #  Physical buttons come from the mouse as:
    #     Big:   1 3
    #     Small: 8 9
    #
    # This makes left small button (8) into the middle, and puts
    #  scrolling on the right small button (9).
    #
    Option "Buttons"            "9"
    Option "ButtonMapping"      "3 8 1 4 5 6 7 2 9"
    Option "EmulateWheel"       "true"
    Option "EmulateWheelButton" "9"
    Option "YAxisMapping"       "4 5"
    Option "XAxisMapping"       "6 7"
EndSection

Everything that swings the mouse from xorg.conf is cut out.
PS: I have a config under my left hand.