stepgen - software step pulse generation
loadrt stepgen step_type=type0[,
type1...]
[
ctrl_type= type0[,
type1...]]
[
user_step_type=#,#...]
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.
-
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.
-
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.
-
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.
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.
The HAL User Manual.