The
state
diagram
shown in Table 4-4
is
executed in
the
interrupt
service
routine
for
the
human
interface
input
device.
Note
that
only keys 0
through
[]],
[i]
through
[U
,
and
[[]
through
rn are allowed
to
select
an
OS.
Other
keys are simply ignored.
This
makes
the
handling of all nationalized keyboards
much simpler.
Because it
is
possible
to
find more OSs
than
there
are lines on
the
display,
the
search scan can
be
paused
and
continued by toggling
the
I Return I
key.
The
line next
to
the
bottom
of
the
screen
indicates
the
current
state
with one of two messages:
SEARCHING
FOR
A
SYSTEM
(Press
RETURN
To
Pause)
or
PAUSED
(Press
RETURN
To
Continue)"
The
menu will
wrap
around
to
the
top
of
the
screen
and
overwrite itself whenever all available
lines are used.
When
the
Boot
ROM
is
paused, all activity stops. Because
the
keyboard
is
polled,
there
may
be
a delay before a key press takes effect.
96
Boot
Rom Functions
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