==============================================================================

   This directory contains the device entries for the Dual DC Motor
Controller.


HARDWARE
   The Dual H-Bridge controller independently controls the speed
and direction of two brushed DC motors designated as '0' and '1'.
The peripheral ties directly to the four switches for each of the
two H-bridges.  The H-bridge switches are designated as 'top'
and 'bottom', and 'left' and 'right'.
   The outputs controlling the bottom switches are inverted.  The
power on defaults at the FPGA pins are all high, which turns on all
the high side switches and turns off all of the low side switches.
That is, the power on default is high side braking.  The pins are
assigned as follows:
      Pin 2:  Top left, motor 0  (1==switch closed)
      Pin 4:  Top right, motor 0
      Pin 6:  Inverted bottom left, motor 0
      Pin 8:  Inverted bottom right, motor 0
      Pin 10: Top left, motor 1
      Pin 12: Top right, motor 1
      Pin 14: Inverted bottom left, motor 1
      Pin 16: Inverted bottom right, motor 1
   The motor speed signals are pulse width modulated (PWM) signals
with a programmable duty cycle between 0 and 100 percent and a
programmable PWM frequency.  The driver tries to minimize the
the time that both motors are being driven.  That is, if both
motors have a PWM speed of 50 percent, then the motors are not
driven at the same time.


DEVICE NODES
The device interfaces to the dual H-bridge controller offer
independent speed, direction, brake or coast mode for each of
the two motors.  The PWM frequency is common to both motors.

.../mode0, .../mode1
   The mode of operation for the motor.  The mode is encoded
as a two character sequence with the code assigned as follows:
        bh  -- high side brake  (power on default)
        bl  -- low side brake
        co  -- coast
        fh  -- forward with high side PWM
        fl  -- forward with low side PWM
        fb  -- forward with both side PWM
        rh  -- reverse with high side PWM
        rl  -- reverse with low side PWM
        rb  -- reverse with both side PWM
        la  -- locked antiphase speed switching

.../speed0, .../speed1
   The PWM 'ON' time as a percentage in the range 0.0 percent
to 100.0 percent.   The speed resolution is 10 bits for a PWM
frequency of 20 KHz and 8 bits for a PWM frequency of 78 KHz.

.../PWMfrequency
   The frequency of the speed PWM signal in Hertz.  The driver
tries to assign a frequency as close as possible to the one
specified.  For example, a requested frequency of 12510 Hertz
might result in an actual PWM frequency of 12500 Hertz.  The
PWM frequency is the same for both motors.

.../slow_start0, .../slow_start1
   The acceleration curve as a list of ten comma separated integers
representing the time (in milliseconds) between each 10 percent
increase from 0 to 100 percent ON time.  For example, the following
specifies a slow start that takes half a second to get to 50 percent
power and three-quarters of a second to get from zero to full power:
        100,100,100,100,100,50,50,50,50,50
The default value for slow_start is off to full power in
zero milliseconds.  That is, the default is to turn off slow
start.

.../slow_stop0, .../slow_stop1
  The deceleration curve as a list of ten comma separated integers
representing the time (in milliseconds) between each 10 percent
decrease from 100 to 0 percent ON time.  For example, the following
specifies a slow stop that takes half a second to get to 50% power
and three-quarters of a second to get from full power to zero:
        100,100,100,100,100,50,50,50,50,50
The default value for slow_stop is full on to full off in
zero milliseconds.  That is, the default is to turn off slow
stop.

.../shootthroughtime
   The anti shoot through timer specifies the time that all
H-bridge switches are forced off when switching directions.
The time is specified in units of nanoseconds in the range
of 0 to 750 nanoseconds in steps of 50 nanoseconds.  The power
on default is 250 nanoseconds.

.../watchdog
   As a safety feature, the driver and FPGA hardware can turn
both motors off if there is no speed or direction update from
the controlling software within the specified time.  The time
is specified in milliseconds and has a maximum value of 1500
milliseconds.  The resolution of the watchdog timer is 100
milliseconds, and a value of zero turns off the watchdog timer.
The default value is 300 milliseconds.