This directory contains a description of the /dev entries for
the quad PWM input peripheral.


HARDWARE
   The quad PWM input peripheral measures the widths of periodic
pulses on each of the four pins on a BaseBoard connector.  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 output pulse widths are reported on a single device node
which gives all four pulse widths on a single newline terminated
line.

.../clksrc
   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
              500000
              100000
               50000
               10000
                5000
                1000
                 500
                 100
                  50
                  10
                   5
                   0

.../waveform
   The clock frequency followed by a comma separated list of values
and times between transitions for all four inputs.  The values
alternate between the four bit value at the input and how long
that value (in clock cycles) was held.  While more difficult to
parse and understand compared to the .../widths data, the raw
sample data retains some of the relative phase information
captured by the peripheral.
   The peripheral captures three transitions for each of the four
input lines.  Each transition has a value and duration measured in
clock cycles.  If all four pins are active the .../samples output
stream will have 24 numbers on each line.
   Only three transitions on a pin are needed to determine the low
and high times (and the thus the frequency and duty cycle).  Input
from a pin is ignored once all three transitions on it have been
recorded.  This input masking prevents a fast changing input from
overflowing the sample buffer.  An 'x' in the example below shows
this masking.  See the protocol reference manual for more details
on the operation of the quad PWM input peripheral.
   As an example, consider the following partial output line from
the .../raw device node for a quad PWM-in peripheral with a 1 MHz
clock source:
   1000000, 5, 201, 7, 336, 5, 24, 7, 1020, 4, 294, 5, 453, .....
The bits and timing represented in this example are
  BITS    HELD FOR ... MICROSECONDS
  0101             201
  0111             336
  0101              24
  0111            1024
  01x0             294
  01x1             453