NAME

       encoder - software counting of quadrature encoder signals

SYNOPSIS

       loadrt encoder [num_chan=num | names=name1[,name2...]]

DESCRIPTION

       encoder  is  used  to  measure  position  by counting the pulses generated by a quadrature
       encoder.  As a software-based implementation it is much less expensive than hardware,  but
       has  a limited maximum count rate.  The limit is in the range of 10KHz to 50KHz, depending
       on the computer speed and other factors.  If better  performance  is  needed,  a  hardware
       encoder counter is a better choice.  Some hardware-based systems can count at MHz rates.

       encoder  supports  a maximum of eight channels.  The number of channels actually loaded is
       set by the num_chan argument when the module is loaded.  Alternatively, specify names= and
       unique names separated by commas.

       The  num_chan=  and  names=  specifiers  are mutually exclusive.  If neither num_chan= nor
       names= are specified, or if num_chan=0 is specified, the default value is three.

       encoder has a one-phase, unidirectional mode called counter.  In this  mode,  the  phase-B
       input  is  ignored;  the counts increase on each rising edge of phase-A.  This mode may be
       useful for counting a unidirectional spindle with a single input line, though  the  noise-
       resistant characteristics of quadrature are lost.

       If  used in counter-mode it is also possible to enable the missing-teeth index mode, where
       a gap in the pulse train of one or more teeth is used as in index marker. This  system  is
       used extensively for automotive crank position sensors.

FUNCTIONS

       encoder.update-counters (no floating-point)
              Does  the  actual  counting,  by  sampling  the  encoder  signals  and decoding the
              quadrature waveforms.  Must be called as frequently as possible,  preferably  twice
              as fast as the maximum desired count rate.  Operates on all channels at once.

       encoder.capture-position (uses floating point)
              Captures  the  raw  counts  from  update-counters  and  performs  scaling and other
              necessary conversion, handles counter rollover, etc.  Can (and  should)  be  called
              less frequently than update-counters.  Operates on all channels at once.

NAMING

       The names for pins and parameters are prefixed as:
         encoder.N. for N=0,1,...,num-1 when using num_chan=num
         nameN. for nameN=name1,name2,... when using names=name1,name2,...

       The encoder.N. format is shown in the following descriptions.

PINS

       encoder.N.counter-mode bit i/o
              Enables  counter  mode.   When  true,  the  counter  counts each rising edge of the
              phase-A input, ignoring the value on phase-B.  This  is  useful  for  counting  the
              output  of  a single channel (non-quadrature) sensor.  When false (the default), it
              counts in quadrature mode.

       encoder.N.counts s32 out
              Position in encoder counts.

       encoder.N.index-enable bit i/o
              When true, counts and position are reset  to  zero  on  the  next  rising  edge  of
              Phase-Z.   At  the  same  time,  index-enable is reset to zero to indicate that the
              rising edge has occurred.

       encoder.N.min-speed-estimate float in (default: 1.0)
              Determine the minimum speed at which velocity will  be  estimated  as  nonzero  and
              postition-interpolated  will  be interpolated.  The units of min-speed-estimate are
              the same as the units of velocity.  Setting this parameter too low will cause it to
              take  a  long  time  for  velocity  to  go  to  0 after encoder pulses have stopped
              arriving.

       encoder.N.phase-A bit in
              Quadrature input for encoder channel N.

       encoder.N.phase-B bit in
              Quadrature input.

       encoder.N.phase-Z bit in
              Index pulse input.

       encoder.N.position float out
              Position in scaled units (see position-scale)

       encoder.N.position-interpolated float out
              Position in scaled units, interpolated between encoder  counts.   Only  valid  when
              velocity  is  approximately  constant and above min-speed-estimate.  Do not use for
              position control.

       encoder.N.position-scale float i/o
              Scale factor, in counts per length unit.  For example, if  position-scale  is  500,
              then 1000 counts of the encoder will be reported as a position of 2.0 units.

       encoder.N.missing-teeth s32 in
              The  number  of  teeth missing from the index gap. For example a 60 tooth gear with
              two teeth shortened to form an index so that there are  58  pulses  per  revolution
              would use a position-scale of 60 and a missing-teeth of 2.

       encoder.N.rawcounts s32 out
              The  raw  count,  as  determined  by  update-counters.   This value is updated more
              frequently than counts and position.  It is also unaffected by reset or  the  index
              pulse.

       encoder.N.reset bit in
              When true, counts and position are reset to zero immediately.

       encoder.N.velocity float out
              Velocity  in  scaled  units  per  second.   encoder  uses an algorithm that greatly
              reduces quantization noise as  compared  to  simply  differentiating  the  position
              output.   When  the magnitude of the true velocity is below min-speed-estimate, the
              velocity output is 0.

       encoder.N.velocity-rpm float out
              Velocity in scaled units per minute. Simply encoder.N.velocity scaled by  a  factor
              of 60 for convenience.

       encoder.N.x4-mode bit i/o
              Enables times-4 mode.  When true (the default), the counter counts each edge of the
              quadrature waveform (four counts per full cycle).  When false, it only counts  once
              per full cycle.  In counter-mode, this parameter is ignored.

       encoder.N.latch-input bit in
       encoder.N.latch-falling bit in (default: TRUE)
       encoder.N.latch-rising bit in (default: TRUE)
       encoder.N.counts-latched s32 out
       encoder.N.position-latched float out
              Update  counts-latched  and  position-latched on the rising and/or falling edges of
              latch-input as indicated by latch-rising and latch-falling.

       encoder.N.counter-mode bit rw
              Enables counter mode.  When true, the  counter  counts  each  rising  edge  of  the
              phase-A  input,  ignoring  the  value  on phase-B.  This is useful for counting the
              output of a single channel (non-quadrature) sensor.  When false (the  default),  it
              counts  in  quadrature mode.  encoder.N.capture-position.tmax s32 rw Maximum number
              of CPU cycles it took to execute this function.

PARAMETERS

       The encoder component has no HAL Parameters.