This directory contains the device entries for the Simple8
general purpose I/O device.


HARDWARE
   The Simple8 I/O has direct access to each of the eight pins
on a BaseBoard connector.   Each GPIO pin can be an input or
an output, and changes at an input pin can trigger the sending
of the pin status up to the host.  The highest numbered pin on
the connector is controlled by the LSB in the control and data
registers.


DEVICE NODES
   The device interfaces for the Simple8 include a read/write
data register, a read-only status register, and a configuration
register to determine direction of the pins and whether or not
a transition on a pin automatically sends pin status up to the
host.

.../status
   The value on the GPIO pins.  A write to this device node
sets an output pin, and a read from it returns the current
value on the pins.  A read requires a round trip over the
USB-serial link and may take a few milliseconds.  Data is
given as an 8-bit hexadecimal number

.../data
   A read-only device node that works with select() and which
reports the new value of the pins after one of the 'watched'
pins changes value.

.../config
   The direction and interrupt configuration of the pins given
as hexadecimal numbers separated by a comma and terminated by a
newline.  The first number gives the direction of the pin where
a set bit indicates an output and a cleared bit indicates an
input.  The second number has a set bit for 'watched' pins
which trigger an automatic send of pin status up to the host.
The power-on default direction for all pins is input and all
pins default to non-watched.  Typical configuration lines
include:
      0xf7, 0xf1
      0xff, 0x0f