scandevs − scan devices

_scandevs()
scans open devices looking for pending input and checks the real-time
clock for expiring timers.
also
moves a pattern through the cpu board leds.
should be called periodically in code sequences where input may exceed
the buffer capabilities of the hardware device or where "interrupt"
characters from the console should take effect as soon as possible.
Code that uses the
facilities should also call
periodically.
The standalone io routines
and
call
frequently, so code that uses these routines often need not explicitly
call
set_timer(3spp)