The switch device serves a one-level directory,
giving access to one read-only file,
switch.
A read returns the value of the development board's
option switch (DS1), represented as a decimal number
from 0 to 15, representing four bits,
each corresponding to one of the four toggles.
Each toggle produces the value 0 when it
is set `ON' and 1 when it is off.
Toggle 1 corresponds to bit
1<<3
in the number,
toggle 2 corresponds to bit
1<<2,
and so on