If we cannot determine current scancode set because either the keyboard
does not respond or responds with bogus value, assume scancode set 1 and
mark the scancode set as uncertain. If we receive the byte 0xF0 while
having the uncertain flag set, swap to scancode set 2. 0xF0 is unused in
scancode set 1 but indicates key release in scancode set 2, so it will
be sent after every key press.
Bananymous
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