How can I send F1..F12 especially F10 in gtkterm?
I have to press
F10 at the right moment to select the boot menu of an APU2 system.
This may not be the answer you're looking for, but don't use
screen /dev/ttyS0 from a terminal, and if that terminal is the "GNOME Terminal", disable the F10 accelerator key from Edit -> Preferences.
If you insist on using
gtkterm, you may try pressing ESC[21~ in order, but it may not work if don't press them fast enough ;-)
Alternatively, add a
macros = F5::<literal-esc>[21~ line in the
[default] section of
~/.gtktermrc and then press F5 in order to send an F10:
$ perl -ne 'print; print "macros = F5::\e[21~\n" if /^\[default/' -i ~/.gtktermrc