Ubuntu Manpage: stepgen - software step pulse generation

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NAME

       stepgen - software step pulse generation

SYNOPSIS

       loadrt        stepgen        step_type=type0[,type1...]       [ctrl_type=type0[,type1...]]
       [user_step_type=#,#...]

DESCRIPTION

stepgen is used to control stepper motors. The maximum step rate depends on the CPU and
other factors, and is usually in the range of 5 kHz to 25 kHz. If higher rates are
needed, a hardware step generator is a better choice.

stepgen has two control modes, which can be selected on a channel by channel basis using
ctrl_type. Possible values are "p" for position control, and "v" for velocity control.
The default is position control, which drives the motor to a commanded position, subject
to acceleration and velocity limits. Velocity control drives the motor at a commanded
speed, again subject to accel and velocity limits. Usually, position mode is used for
machine axes. Velocity mode is reserved for unusual applications where continuous
movement at some speed is desired, instead of movement to a specific position. (Note that
velocity mode replaces the former component freqgen.)

stepgen can control a maximum of 16 motors. The number of motors/channels actually loaded
depends on the number of type values given. The value of each type determines the outputs
for that channel. Position or velocity mode can be individually selected for each
channel. Both control modes support the same 16 possible step types.

By far the most common step type is '0', standard step and direction. Others include
up/down, quadrature, and a wide variety of three, four, and five phase patterns that can
be used to directly control some types of motor windings. (When used with appropriate
buffers of course.)

Some of the stepping types are described below, but for more details (including timing
diagrams) see the stepgen section of the HAL reference manual.

type 0: step/dir
Two pins, one for step and one for direction. make-pulses must run at least twice
for each step (once to set the step pin true, once to clear it). This limits the
maximum step rate to half (or less) of the rate that can be reached by types 2-14.
The parameters steplen and stepspace can further lower the maximum step rate.
Parameters dirsetup and dirhold also apply to this step type.

type 1: up/down
Two pins, one for 'step up' and one for 'step down'. Like type 0, make-pulses must
run twice per step, which limits the maximum speed.

type 2: quadrature
Two pins, phase-A and phase-B. For forward motion, A leads B. Can advance by one
step every time make-pulses runs.

type 3: three phase, full step
Three pins, phase-A, phase-B, and phase-C. Three steps per full cycle, then
repeats. Only one phase is high at a time - for forward motion the pattern is A,
then B, then C, then A again.

type 4: three phase, half step
Three pins, phases A through C. Six steps per full cycle. First A is high alone,
then A and B together, then B alone, then B and C together, etc.

types 5 through 8: four phase, full step
Four pins, phases A through D. Four steps per full cycle. Types 5 and 6 are
suitable for use with unipolar steppers, where power is applied to the center tap
of each winding, and four open-collector transistors drive the ends. Types 7 and 8
are suitable for bipolar steppers, driven by two H-bridges.

types 9 and 10: four phase, half step
Four pins, phases A through D. Eight steps per full cycle. Type 9 is suitable for
unipolar drive, and type 10 for bipolar drive.

types 11 and 12: five phase, full step
Five pins, phases A through E. Five steps per full cycle. See HAL reference
manual for the patterns.

types 13 and 14: five phase, half step
Five pins, phases A through E. Ten steps per full cycle. See HAL reference manual
for the patterns.

type 15: user-specified
This uses the waveform specified by the user_step_type module parameter, which may
have up to 10 steps and 5 phases.

FUNCTIONS

       stepgen.make-pulses (no floating-point)
              Generates the step pulses, using information  computed  by  update-freq.   Must  be
              called as frequently as possible, to maximize the attainable step rate and minimize
              jitter.  Operates on all channels at once.

       stepgen.capture-position (uses floating point)
              Captures position feedback value from the high speed code and makes it available on
              a pin for use elsewhere in the system.  Operates on all channels at once.

       stepgen.update-freq (uses floating point)
              Accepts  a  velocity  or  position  command  and  converts it into a form usable by
              make-pulses for step generation.  Operates on all channels at once.

PINS

stepgen.N.counts s32 out
The current position, in counts, for channel N. Updated by capture-position.

stepgen.N.position-fb float out
The current position, in length units (see parameter position-scale). Updated by
capture-position. The resolution of position-fb is much finer than a single step.
If you need to see individual steps, use counts.

stepgen.N.enable bit in
Enables output steps - when false, no steps are generated.

stepgen.N.velocity-cmd float in (velocity mode only)
Commanded velocity, in length units per second (see parameter position-scale).

stepgen.N.position-cmd float in (position mode only)
Commanded position, in length units (see parameter position-scale).

stepgen.N.step bit out (step type 0 only)
Step pulse output.

stepgen.N.dir bit out (step type 0 only)
Direction output: low for forward, high for reverse.

stepgen.N.up bit out (step type 1 only)
Count up output, pulses for forward steps.

stepgen.N.down bit out (step type 1 only)
Count down output, pulses for reverse steps.

stepgen.N.phase-A thru phase-E bit out (step types 2-14 only)
Output bits. phase-A and phase-B are present for step types 2-14, phase-C for
types 3-14, phase-D for types 5-14, and phase-E for types 11-14. Behavior depends
on selected stepping type.

PARAMETERS

stepgen.N.frequency float ro
The current step rate, in steps per second, for channel N.

stepgen.N.maxaccel float rw
The acceleration/deceleration limit, in length units per second squared.

stepgen.N.maxvel float rw
The maximum allowable velocity, in length units per second. If the requested
maximum velocity cannot be reached with the current combination of scaling and
make-pulses thread period, it will be reset to the highest attainable value.

stepgen.N.position-scale float rw
The scaling for position feedback, position command, and velocity command, in steps
per length unit.

stepgen.N.rawcounts s32 ro
The position in counts, as updated by make-pulses. (Note: this is updated more
frequently than the counts pin.)

stepgen.N.steplen u32 rw
The length of the step pulses, in nanoseconds. Measured from rising edge to
falling edge.

stepgen.N.stepspace u32 rw (step types 0 and 1 only)
The minimum space between step pulses, in nanoseconds. Measured from falling edge
to rising edge. The actual time depends on the step rate and can be much longer.
If stepspace is 0, then step can be asserted every period. This can be used in
conjunction with hal_parport's auto-resetting pins to output one step pulse per
period. In this mode, steplen must be set for one period or less.

stepgen.N.dirsetup u32 rw (step type 0 only)
The minimum setup time from direction to step, in nanoseconds periods. Measured
from change of direction to rising edge of step.

stepgen.N.dirhold u32 rw (step type 0 only)
The minimum hold time of direction after step, in nanoseconds. Measured from
falling edge of step to change of direction.

stepgen.N.dirdelay u32 rw (step types 1 and higher only)
The minimum time between a forward step and a reverse step, in nanoseconds.

TIMING

       There are five timing parameters which control the output waveform.  No step type uses all
       five, and only those which will be  used  are  exported  to  HAL.   The  values  of  these
       parameters  are  in  nano-seconds,  so  no  recalculation  is  needed when changing thread
       periods.  In the timing diagrams  that  follow,  they  are  identified  by  the  following
       numbers:

       (1) stepgen.n.steplen

       (2) stepgen.n.stepspace

       (3) stepgen.n.dirhold

       (4) stepgen.n.dirsetup

       (5) stepgen.n.dirdelay

       For  step type 0, timing parameters 1 thru 4 are used.  The following timing diagram shows
       the output waveforms, and what each parameter adjusts.

                      _____         _____               _____
           STEP  ____/     \_______/     \_____________/     \______
                     |     |       |     |             |     |
           Time      |-(1)-|--(2)--|-(1)-|--(3)--|-(4)-|-(1)-|
                                                 |__________________
           DIR   ________________________________/

       For step type 1, timing parameters 1, 2, and 5 are used.   The  following  timing  diagram
       shows the output waveforms, and what each parameter adjusts.

                    _____       _____
           UP    __/     \_____/     \________________________________
                   |     |     |     |         |
           Time    |-(1)-|-(2)-|-(1)-|---(5)---|-(1)-|-(2)-|-(1)-|
                                               |_____|     |_____|
           DOWN  ______________________________/     \_____/     \____

       For  step  types  2  and higher, the exact pattern of the outputs depends on the step type
       (see the HAL manual for a full listing).  The outputs change from one state to another  at
       a  minimum  interval of steplen.  When a direction change occurs, the minimum time between
       the last step in one direction and the first in the other direction is the sum of  steplen
       and dirdelay.