This directory contains a description of the /dev entries for
the octal PWM output peripheral.


HARDWARE
   The octal PWM output peripheral drives eight output pins with
a square wave of independently programmable frequency and duty
cycle.  The device node .../pwmout0 corresponds to pin 2 on the
BaseBoard connector.  Pin 16 is controlled by .../pwmout7.
   Pulse widths are measured with 16 bits of accuracy for both
the high and low periods of a pulse.  The clock source driving
the pulse width counters ranges from 5 Hertz to 20 MegaHertz. 


DEVICE NODES
   The eight outputs each have a separate device node to accept
the pulse low and high times.  There is a device node to specify
the controlling clock frequency and another node that has the raw
data that is sent to the peripheral. 

   The frequency of the clock that drives the width counters.  A
clock frequency of zero turns off the peripheral.  The frequency
is given in Hertz and must be one of the following:
            20000000
            10000000
             5000000
             1000000
             5000000
             1000000
              500000
              100000
               50000
               10000
                500
                100
                 50
                 10
                  5
                  0

.../waveform
   The clock frequency followed by a comma separated list of values
and times between transitions for all eight outputs.  The values
alternate between the eight bit value at the output (in hex) and how
long that value (in clock cycles) is to be held.  The raw sample data 
conveys the relative timing for each output.
   As an example, consider the following ASCII art timing diagram:

|++++|++++|++++|++++|++++|++++|++++|++++|++++|++++|
__________|---------|______________________________ pwmout0
______________________________|---------|__________ pwmout1
_______________|----|______________________________ pwmout2
______________________________|----|_______________ pwmout3
v         v    v    v         v    v    v
0         1    5    0         a    2    0           Value
----10------5----5-------10-----5----5-------10---- Interval

The initial value, 0000, is indicated by the first 'v' on the above
line.  The first time is the interval between the first v and second.
The second value is 0001 and the second interval time is the time
between the second and third v's.  If each tick mark is 1 microsecond
then the above pattern could be generated with the following input
string:
     1000000,0,10,1,5,5,5,0,10,a,5,2,5,0,10