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This directory contains the device entries for the quad Parallax
Ping interface.


HARDWARE
The quad Parallax Ping interface makes each pin on the connector
into a channels of bidirectional I/O that connects directly to a
Parallax Ping ultrasonic range sensor..  The first channel appears
on the BaseBoard connector pin 2 or on pin 10 depending on the slot
number for the peripheral.  The fourth channel is on pin 8 or 16.
The ultrasonic pings are sent out sequentially so that they do not
interfere with each other.


DEVICE NODES
The device interfaces to the quad Ping interface include an enable
register and a read-only device node that gives the distances
reported by the sensors.

.../enable
   A single hexadecimal word terminated by a newline.  The sensors 
may be individually turned on or off.  The LSB of the enable register 
corresponds to the lowest numbered sensor, 0.  A set bit enables the 
sensor and a cleared bit disables it.  You may wish to disable unused 
pins.  Examples of enable words are as follows:
     0x2  -- enables only sensor 1
     0x5  -- enables sensors 0 and 2
     0xf  -- enables all sensors 

.../distance
   The distance reported by each sensor as the readings come in.
The distance device node is a broadcast device and file descriptors
for it will work with the select() statement.  The output is a digit
that indicates the channel number and the distance given in units of
one-tenth of an inch.  The channel number and readings are separated
by a comma and terminated by a newline.  A distance of zero indicates
that the sensor is not connected or is not responding.
   Typical output from the distance device node might appear as:
     0, 1055
     1, 55
     2, 0
     3, 1848
     0, 1094