stepper

stepper

Step-motor position controller. Drives a STEP / DIR / EN style driver chip (DRV8825, A4988, TB6600, generic L297 + Darlington, …) by calling caller-supplied pin-write functions on a periodic tick. Position is signed int32_t, so negative coordinates work natively.

The controller is dirt simple: you tell it where to go with stepper_move_relative / stepper_move_to, it generates STEP pulses on each subsequent stepper_tick until current == target. No acceleration / deceleration profile (constant rate); add one in your application code if you need it.

Quick example

#include "stepper.h"

static void step_pin(uint8_t v) { GPIO_WritePin(STEP_PORT, STEP_PIN, v); }
static void dir_pin (uint8_t v) { GPIO_WritePin(DIR_PORT,  DIR_PIN,  v); }
static void en_pin  (uint8_t v) { GPIO_WritePin(EN_PORT,   EN_PIN,   v); }

st_stepper motor;

void init_motor(void)
{
    /* On this wiring, DIR=1 turns clockwise. Pass NULL for the EN
     * callback if your driver has no enable line. */
    stepper_init(&motor, step_pin, dir_pin, en_pin,
                 /* cw  */ 1,
                 /* ccw */ 0);

    /* Tune speed: tick_rate / 2 / (1 + delay_max). On a 1 kHz tick:
     *   delay_max=0 -> 500 step/s
     *   delay_max=1 -> 250 step/s
     *   delay_max=4 -> 100 step/s */
    stepper_set_delay(&motor, 1);
    stepper_enable(&motor, 1);
}

void timer_1ms_isr(void) { stepper_tick(&motor); }   /* 1 kHz */

void some_command(void)
{
    stepper_move_relative(&motor, 200);              /* turn 200 steps CW */
    while (stepper_is_busy(&motor)) {
        /* let the ISR work; do other things */
    }
}

API

Function	Purpose
stepper_init(s, step_fn, dir_fn, en_fn, cw, ccw)	Wire up the three pin callbacks (en may be NULL) and the DIR-pin values that mean clockwise / counter-clockwise on your board.
stepper_tick(s)	Call from a periodic source. Each tick toggles STEP up to once; two ticks = one full pulse = one step of motion.
stepper_move_relative(s, delta)	Adjust target by delta (signed).
stepper_move_to(s, target)	Set absolute target position.
stepper_set_delay(s, n)	Inter-toggle delay. Output rate = tick_rate / 2 / (1 + n).
stepper_enable(s, on)	Drive the EN pin via the registered callback. No-op if no EN was registered.
stepper_position(s)	Current position.
stepper_target(s)	Current target.
stepper_is_busy(s)	1 if current != target.

Notes

• Multi-instance safe. All state lives in st_stepper; you can drive several motors from the same tick ISR by calling stepper_tick once per motor.
• No acceleration profile. Constant-rate from current_pos to target_pos. If you need trapezoidal / S-curve ramping, layer it on top by adjusting stepper_set_delay over time.
• Speed control = delay_max. Output rate is tick_rate / 2 / (1 + delay_max). With a 1 kHz tick this gives 500 / 250 / 167 / 125 / 100 Hz at delay_max = 0..4.
• The DIR pin is updated only on direction transitions, giving driver chips like DRV8825 their required setup-time margin before the next rising STEP edge.

Build the self-test

make test       # from this directory

Drives a virtual controller through several moves with mock pin callbacks and verifies the STEP / DIR call sequences, the position counter, the wrap from CW to CCW direction, the delay_max timing, and the EN-pin pass-through. Prints stepper: All OK. on success.

Use in another project

Drop stepper.h and stepper.c into your sources.

License

MIT.