servo_limit.c File Reference

Search for a servo mechanical limit by current: the state machine. More...

#include "servo_limit.h"
#include <string.h>

Macros
#define	BASELINE_STEPS   3u

Functions
static bool	elapsed (uint32_t now, uint32_t then, uint32_t ms)
	Tell whether a millisecond span has elapsed.
static uint16_t	clamp_travel (const servo_limit_cfg_t *cfg, int32_t us)
	Clamp a pulse width to the search travel and the pulse range.
void	servo_limit_defaults (servo_limit_cfg_t *cfg, uint16_t centre_us, bool positive)
	Defaults for a hobby servo on a control surface.
void	servo_limit_init (servo_limit_t *lf, const servo_limit_cfg_t *cfg)
	Start a limit search.
static void	finish (servo_limit_t *lf, servo_limit_state_t state, servo_limit_fault_t fault)
	Finish the search with the surface returned to centre.
static bool	advance (servo_limit_t *lf)
	Move one step further out.
static void	judge (servo_limit_t *lf, float avg_a)
	One position's averaged current has arrived; decide what it means.
uint16_t	servo_limit_step (servo_limit_t *lf, float current_a, uint32_t now_ms)
	Advance the search with one current reading, and return the pulse width the servo should be commanded to.
float	servo_limit_progress (const servo_limit_t *lf)
	How far the search has gone, 0..1, for a progress bar.

Detailed Description

Search for a servo mechanical limit by current: the state machine.

SPDX-License-Identifier: MIT

Function Documentation

advance()

bool advance ( servo_limit_t * lf )

static

Move one step further out.

A step that would pass the end of the permitted travel stops at that end, so the end itself is measured. With the end measured free, the surface is free over the whole range asked about, and that is reported as NO_LIMIT rather than as a mechanical limit.

Returns false if the search ended here.

Parameters

lf	Search state to advance.

Returns

false if the search ended here, true if the command moved.

clamp_travel()

uint16_t clamp_travel ( const servo_limit_cfg_t * cfg, int32_t us )

static

Clamp a pulse width to the search travel and the pulse range.

Parameters

cfg	Configuration whose centre_us and max_travel_us bound the travel.
us	Pulse width to clamp, us.

Returns

the clamped width, SERVO_LIMIT_MIN_US to SERVO_LIMIT_MAX_US.

elapsed()

bool elapsed ( uint32_t now, uint32_t then, uint32_t ms )

inlinestatic

Tell whether a millisecond span has elapsed.

Parameters

now	Current time, ms.
then	Start of the span, ms.
ms	Span length, ms.

Returns

true when now - then is at least ms, across a counter wrap.

finish()

void finish ( servo_limit_t * lf, servo_limit_state_t state, servo_limit_fault_t fault )

static

Finish the search with the surface returned to centre.

Parameters

lf	Search state to update.
state	Final state to store.
fault	Fault code to store.

judge()

void judge ( servo_limit_t * lf, float avg_a )

static

One position's averaged current has arrived; decide what it means.

Parameters

lf	Search state to update.
avg_a	Current averaged over the measure phase at this position, A.

servo_limit_defaults()

void servo_limit_defaults	(	servo_limit_cfg_t *	cfg,
		uint16_t	centre_us,
		bool	positive )

Defaults for a hobby servo on a control surface.

Parameters

cfg	Configuration to fill. Does nothing when NULL.
centre_us	Centre pulse width, us.
positive	true to step toward longer pulse widths, false toward shorter ones; the step is 10us either way.

servo_limit_init()

void servo_limit_init	(	servo_limit_t *	lf,
		const servo_limit_cfg_t *	cfg )

Start a limit search.

Parameters

lf	Search state to initialise. Does nothing when NULL.
cfg	Configuration to copy. Does nothing when NULL.

servo_limit_progress()

float servo_limit_progress

(

const servo_limit_t *

lf

)

How far the search has gone, 0..1, for a progress bar.

Parameters

lf	Search state.

Returns

progress from 0.0 (centre) to 1.0; 1.0 when the state is not RUNNING, 0.0 when lf is NULL or max_travel_us is 0.

servo_limit_step()

uint16_t servo_limit_step	(	servo_limit_t *	lf,
		float	current_a,
		uint32_t	now_ms )

Advance the search with one current reading, and return the pulse width the servo should be commanded to.

Call it at the sampling rate of the current sensor. Calling after the search has finished is safe; the returned width then holds the servo at centre, so a finished search leaves no surface deflected.

Parameters

lf	Search state. A NULL lf gives 0.
current_a	Current reading, A. At or above hard_limit_a, or NaN, aborts the search.
now_ms	Time of the reading, ms.

Returns

pulse width to command, us; 0 when lf is NULL.