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4.4 General Notes on Using <NumLock> for the <PF1> Key on Unix Systems

Making the physical <NumLock> key available for use in the EDT Emulation requires some modification to the default X Window settings. Since the keycode assignments vary from system to system, some investigation is needed to see how to do this on a particular system.

You will need to look at the output generated by xmodmap invoked with the "-pm" switch. For example, on RedHat GNU/Linux 5.2 on a PC, we get the following output when running ‘xmodmap -pm’:

     xmodmap:  up to 2 keys per modifier, (keycodes in parentheses):
     
     shift       Shift_L (0x32),  Shift_R (0x3e)
     lock        Caps_Lock (0x42)
     control     Control_L (0x25),  Control_R (0x6d)
     mod1        Alt_L (0x40),  Alt_R (0x71)
     mod2        Num_Lock (0x4d)
     mod3
     mod4
     mod5        Scroll_Lock (0x4e)

Note that Num_Lock is assigned to the modifier ‘mod2’. This is what hides Num_Lock from being seen by Emacs.

Now, ‘xmodmap -pke’ yields:

        .
        .
        .
     keycode  77 = Num_Lock Pointer_EnableKeys
        .
        .
        .
     keycode  96 = F12
        .
        .
        .

So, in RedHat GNU/Linux 5.2 on a PC, Num_Lock generates keycode 77. The following steps are taken:

  1. clear the assignment of Num_Lock to mod2;
  2. swap the keycodes assigned to F12 and Num_Lock;
  3. assign Num_Lock back to mod2.

The .xmodmaprc file looks like this:

     ! File:  .xmodmaprc
     !
     ! Set up PC keypad under GNU/Linux for the Emacs EDT Emulation
     !
     clear  mod2
     keycode  77 = F12
     keycode  96 = Num_Lock Pointer_EnableKeys
     add mod2 = Num_Lock

So, after executing ‘xmodmap .xmodmaprc’, a press of the physical <F12> key looks like a Num_Lock keypress to X. Also, a press of the physical <NumLock> key looks like a press of the <F12> key to X.

Now, edt-mapper.el will see ‘f12’ when the physical <NumLock> key is pressed, allowing the <NumLock> key to be used as the EDT <PF1> (<GOLD>) key.