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This directory contains the device entries for the buttons
and LEDs on the BaseBoard4.


HARDWARE
    Each BaseBoard4 has three buttons (S1, S2 and S3) and
eight LEDs (LED0 to LED7).  The bb4io peripheral is standard
on all FPGA builds for the BaseBoard4.


DEVICE NODES

.../leds
    The value of the LEDs as an eight bit hexadecimal number
terminated by a newline.  This is a read-write device node.

.../buttons
    The value of the buttons as number between 0 and 7 and 
terminated by a newline.  A read on this node blocks until
the status of the buttons changes.  This is a read-only
device node.