This directory contains the device entries for the Octal Servo
Controller.


HARDWARE
   The Octal Servo Controller provides eight servo pulses with each
pulse width accurate to 50 nanoseconds.  The cycle time for all
eight signals is 20 milliseconds.
   The servos are numbered from 0 to 7 with servo 0 on the lowest
number pin on the connector (pin 2).  Servo 7 is on the highest
numbered pin (pin 16).  The servo signals are not inverted and the
power-on default values are all high.


DEVICE NODES
   The device interfaces to the Octal Servo Controller include
individual controls for each servo as well as a control which
manipulates the servos as a group.

.../servo0, .../servo1, .../servo2, ...  .../servo7
   Commands to move the servos are a pair of comma separated integers.
Each command ends with a newline character.  The first number is the
target pulse width in nanoseconds.  The second number specifies how
long, in milliseconds, it should take to get to that pulse width.
   A pulse width of 0 sets the output high which leaves the servo
undriven.   A move duration of 0 milliseconds causes the change to
take effect immediately.  The default value is 0.
   Reading the servo device node gives the current servo pulse width
in nanoseconds, followed by a comma, a zero, and a newline.  The value
that you read will not be the value that you write if you give a long
transition time.  That is, the read may capture the instantaneous
value as the pulse width transitions from the old value to the new
value.  Here are some common examples:
   # give servo1 a 1.00 millisecond width
echo '1000000, 0' > servo1
   # transition servo2 to a width of 2 ms and take 100 ms to do it.
echo '2000000, 100' >servo2
   # get the current pulse width of servo 3
cat servo3


.../servogroup
   The servogroup device node is a convenient way to move all of the
servos in a coordinated move.  The command syntax is a comma separated
list of integer  pulse widths followed by the number of milliseconds
that the move should take.   A pulse width of zero sets that output
high and pulse width of -1 takes that pulse width out of the group move.
Some examples may help:
   # Move the first four pulse widths to center and take 300 ms to do it
echo '1500000, 1500000, 1500000, 1500000, -1, -1, -1, -1,300' > servogroup
   A read of servogroup returns the current positions of all servos as
a comma separate list of pulse widths measured in nanoseconds.  The read
string has a trailing comma, zero, and newline.
   As a safety feature, a write to an individual servo take precedence
over a group move, so that a write of zero to an individual servo will
turn off the servo even if it is in the middle of a group move.