drivers: stepper: introduce rudimentary trapezoidal ramp control #88564

jilaypandya · 2025-04-13T19:25:49Z

Trapezoidal Ramp Control for Stepper Motors:

The idea is to create a ramp lib that can be integrated in any driver, the step counting for the driver itself stays unaffected by integration a ramp lib

I have been using Shell to see how the ramping looks like.

Starting This PR to get some early feedback.

Integration in driver

References:
https://www.boost.org/doc/libs/1_81_0/libs/safe_numerics/example/stepper-motor.pdf
Equation 13 in the above mentioned paper can also be seen in this app note.
https://ww1.microchip.com/downloads/en/Appnotes/doc8017.pdf (Thanks @andre-stefanov :) )

Known open points:

Integrate ramp control for stepper_run as well
use of sqrt in calculate_start_velocity, this function gets called once when the ramping starts from zero-velocity
copied isqrt
Implement unit tests
Introduce DT based selection of trapezoidal ramp, allowing inclusion of other ramps in future

Update: 23.04.2025
Thanks @andre-stefanov for contributing unit-tests :)

drivers/stepper/ramp/ramp.h

include/zephyr/drivers/stepper.h

drivers/stepper/ramp/ramp_trapezoidal.c

andre-stefanov · 2025-04-13T21:40:49Z

include/zephyr/drivers/stepper.h

+	/** Ramp acceleration in micro-steps per second squared */
+	uint32_t acceleration;
+	/** Ramp maximum velocity in micro-steps per second */
+	uint32_t max_velocity;


is max_velocity really needed? next step interval depends only on current interval and acceleration/deceleration values.

the actual limit will be given by the requested stepper interval

Trying to depict a trapezoidal ramp. I am also using max_velocity to check for valid_timing in move_by and move_to. But i'll check this again for sure if it is actually needed :).

In my experience, the speed set via set_microstep_interval is sufficient.

Okay we can use that function, but we definitely need to have a better name for it though. set_microstep_interval atleast imo sounds like this interval will take place with immediate effect. Probably something like set_target_step_interval ?

Using the current micro-step interval implementation also requires changes to pre-decel-steps, as it is dependent on the speed. My recommendation would be to use the current micro-step interval in combination with the deceleration value for this

jbehrensnx · 2025-04-14T06:32:30Z

include/zephyr/drivers/stepper.h

+	/** Ramp acceleration in micro-steps per second squared */
+	uint32_t acceleration;
+	/** Ramp maximum velocity in micro-steps per second */
+	uint32_t max_velocity;


In my experience, the speed set via set_microstep_interval is sufficient.

drivers/stepper/gpio_stepper_controller.c

jbehrensnx · 2025-04-14T07:07:13Z

drivers/stepper/gpio_stepper_controller.c

+
+	K_SPINLOCK(&data->lock) {
+		data->ramp_common.ramp_profile.acceleration = ramp_profile->acceleration;
+		data->ramp_common.ramp_profile.max_velocity = ramp_profile->max_velocity;


You don't need max_velocity, you already have set_microstep_interval.

We need to find a consensus on how to rename that function, set_microstep_interval imo signifies more like a tick time, could be compared with for instance , can_set_bitrate.

I would say, once this PR is merged, the CONFIG_STEPPER_RAMP can be deleted and all motors should support ramping by default.

jbehrensnx · 2025-04-14T07:13:37Z

drivers/stepper/ramp/Kconfig

+
+if STEPPER_RAMP
+
+config STEPPER_RAMP_TRAPEZOIDAL


I would prefer a dt-binding instead to allow for a per stepper-controller decision on using ramps or not.

done. However, you would need one such variable for the source to be included, or is there a better way?

I think there is a Kconfig extension for checking if a property is present on a compatible:

drivers/dma/Kconfig.mcux_edma:12: depends on $(dt_compat_any_has_prop,$(EDMA_COMPAT),$(REV_PROP),2)

but nothing like dt_any_of_driver_class_has_prop, which would be neat.

jbehrensnx · 2025-04-14T07:20:55Z

drivers/stepper/ramp/ramp_trapezoidal.c

+	switch (ramp_data->current_ramp_state) {
+	case STEPPER_RAMP_STATE_ACCELERATION:
+		ramp_data->ramp_actual_position++;
+		new_step_interval_in_ns = current_step_interval_in_ns -


You cant always use the approximation. You will need to use the accurate algorithm using the sqrt for a number of steps after starting accelerating and a couple of steps before stopping when decelerating. This is because of the approximation error.

jbehrensnx · 2025-04-14T07:24:48Z

My PR 88342 already uses the same algorithm (through I forgot to mention the algorithm admittedly) for a step-dir implementation. Several decisions made during development for that are relevant for this PR as well, so it should be included in the discussion.

dts/bindings/stepper/ramp-parameters.yaml

dipakgmx · 2025-04-14T21:20:39Z

This is not related to the changes made in this PR, but could the functions move_to & move_by call either of them, I mean, in move_by, call move_to(current_pos+move_by_target)? It seems to me that some bits of code are repeated in both the functions (or thats what I felt when reviewing)

drivers/stepper/stepper_common.h

samples/drivers/stepper/generic/Kconfig

faxe1008 · 2025-04-22T15:00:50Z

include/zephyr/drivers/stepper/stepper_ramp.h

+/**
+ * @brief Stepper ramp profile
+ */
+struct stepper_ramp_profile {


Why not have this in stepper.h directly?

coz then ramp.h would need to include stepper.h and i wanted to keep the ramp.h as decoupled from the stepper.h as possible.

Need some feedback on this actually, how about instead of stepper_set_ramp_profile(ramp_profile), we do something like stepper_set_timing_data(accel, max_velocity, decel) and then we put ramp_profile in ramp.h

done moved to stepper.h

faxe1008 · 2025-04-22T15:06:14Z

drivers/stepper/ramp/Kconfig

+
+if STEPPER_RAMP
+
+config STEPPER_RAMP_TRAPEZOIDAL


I think there is a Kconfig extension for checking if a property is present on a compatible:

drivers/dma/Kconfig.mcux_edma:12: depends on $(dt_compat_any_has_prop,$(EDMA_COMPAT),$(REV_PROP),2)

but nothing like dt_any_of_driver_class_has_prop, which would be neat.

faxe1008 · 2025-04-22T15:10:51Z

drivers/stepper/ramp/ramp.h

+ */
+typedef void (*stepper_ramp_reset_ramp_runtime_data_t)(const struct stepper_ramp_config *config,
+						       struct stepper_ramp_common *ramp_common,
+						       const bool is_stepper_dir_changed,


would it maybe make the API more stable when you move is_stepper_dir_changed etc. into the runtime data?

yep that's correct :), Will do it in the next push.

drivers/stepper/gpio_stepper_controller.c

faxe1008 · 2025-04-25T13:09:58Z

drivers/stepper/gpio_stepper_controller.c

@@ -129,6 +172,10 @@ static void update_direction_from_step_count(const struct device *dev)
 	} else {
 		LOG_ERR("Step count is zero");
 	}
+	if (data->direction != direction) {


Directly return this?

faxe1008 · 2025-04-25T13:10:39Z

drivers/stepper/gpio_stepper_controller.c

+	}
+	return false;
+#else
+	if (data->delay_in_ns > 0) {


Return this directly

jbehrensnx · 2025-04-28T07:47:39Z

drivers/stepper/gpio_stepper_controller.c

+#ifdef CONFIG_STEPPER_RAMP
+	if (data->ramp_common.ramp_runtime_data.current_ramp_state ==
+	    STEPPER_RAMP_STATE_PRE_DECELERATION) {
+		if (data->direction == STEPPER_DIRECTION_NEGATIVE) {


The non ramp part uses a if DIRECTION_POSITIVE else if DIRECTION_NEGATIVE ordering and I would keep it consistent.

thanks. done

jbehrensnx · 2025-04-28T08:07:27Z

drivers/stepper/ramp/ramp_trapezoidal.c

+	switch (state) {
+	case STEPPER_RAMP_STATE_ACCELERATION:
+		new_step_interval = current_step_interval -
+				    (2 * current_step_interval) / (4 * ramp_position + 1);


Suggested change

(2 * current_step_interval) / (4 * ramp_position + 1);

(2 * current_step_interval) / (4 * ramp_position + 3);

Using this, you effectively add 0.5 to ramp position, calculating the new interval based on the middle of the ramp segment and not the start, improving acceleration behavior. Note that your deceleration calculation already does this.

drivers/stepper/ramp/ramp_trapezoidal.c

jbehrensnx · 2025-04-28T08:45:26Z

drivers/stepper/ramp/ramp_trapezoidal.c

+	case STEPPER_RAMP_STATE_PRE_DECELERATION:
+		if ((current_step_interval_in_ns >
+		     ramp_data->ramp_stop_step_interval_threshold_in_ns)) {
+			uint64_t start_velocity =


This is an interval and not a velocity.

jbehrensnx · 2025-04-28T08:52:05Z

include/zephyr/drivers/stepper.h

+	/** Ramp acceleration in micro-steps per second squared */
+	uint32_t acceleration;
+	/** Ramp maximum velocity in micro-steps per second */
+	uint32_t max_velocity;


Using the current micro-step interval implementation also requires changes to pre-decel-steps, as it is dependent on the speed. My recommendation would be to use the current micro-step interval in combination with the deceleration value for this

tests/drivers/stepper/ramp/src/main.c

Introduce rudimentary trapezoidal ramp control using following paper: https://www.boost.org/doc/libs/1_81_0/libs/safe_numerics/example/stepper-motor.pdf Signed-off-by: Jilay Pandya <[email protected]>

testing following criteria: - distance profile - first acceleration interval - next step intervals Signed-off-by: Andre Stefanov <[email protected]>

jbehrensnx · 2025-04-28T09:19:14Z

As a general thing, in my experience, you need picosecond resolution for the ramp calculations, which are then converted to nanoseconds for the stepper controllers (but saving the picosecond values for the next step). Not sure if your 0.676 to counteract approximation inaccuracies reduces accuracy so much that this no longer matters.

Could could you maybe test if in an acceleration towards 50 or 200 steps/s in 1 sec actually takes 1 second? I remember during my development using this algorithm that I often got inaccuracies in the range of 20%, something that is not noticeable when using only the console without printing the times.

github-actions bot added area: Stepper area: Samples Samples area: Devicetree labels Apr 13, 2025

github-actions bot requested review from bjarki-andreasen, decsny, dipakgmx, fabiobaltieri, faxe1008, galak, jbehrensnx, kartben, nashif and rruuaanng April 13, 2025 19:26

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jilaypandya force-pushed the feature/introduce-rudimentary-ramp branch from 3eb28c1 to d4a1f59 Compare April 13, 2025 19:31

jilaypandya mentioned this pull request Apr 13, 2025

Stepper API: Set Ramp Profile #88563

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drivers: stepper: introduce trapezoidal ramp control

6d0b2cf

Introduce rudimentary trapezoidal ramp control using following paper: https://www.boost.org/doc/libs/1_81_0/libs/safe_numerics/example/stepper-motor.pdf Signed-off-by: Jilay Pandya <[email protected]>

tests: added unit tests for stepper ramp api

7723317

testing following criteria: - distance profile - first acceleration interval - next step intervals Signed-off-by: Andre Stefanov <[email protected]>

jilaypandya force-pushed the feature/introduce-rudimentary-ramp branch from 8d25028 to 7723317 Compare April 28, 2025 09:19

jilaypandya closed this May 10, 2025

jbehrensnx mentioned this pull request May 12, 2025

Split Stepper Motion Controller <-> Stepper Driver #89786

Open

	(2 * current_step_interval) / (4 * ramp_position + 1);
	(2 * current_step_interval) / (4 * ramp_position + 3);

drivers: stepper: introduce rudimentary trapezoidal ramp control #88564

drivers: stepper: introduce rudimentary trapezoidal ramp control #88564

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jilaypandya commented Apr 13, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Trapezoidal Ramp Control for Stepper Motors:

Integration in driver

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jilaypandya Apr 13, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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jbehrensnx commented Apr 14, 2025

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jilaypandya commented Apr 13, 2025 •

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