fix div by 0 bug

Inc/stepper.h

@@ -10,7 +10,7 @@ typedef struct {
     GPIO_TypeDef* home_port;
     uint8_t home_pin;
     uint8_t homed:1;
-    uint8_t moving:1;
+    uint8_t trigger_step:1;
     int16_t pos;
     int16_t speed;
     int16_t ramp_to_speed;

Src/stepper.c

@@ -77,7 +77,10 @@ void do_steps(){
     timer++;
 
     for(uint8_t i=0; i<(sizeof(steppers)/sizeof(stepper_T)); i++){
-        if(steppers[i].ramp_to_speed != 0 && steppers[i].next_step == timer){
+        if((steppers[i].ramp_to_speed != 0 && steppers[i].next_step == timer) || steppers[i].trigger_step){
+            /* reset trigger */
+            steppers[i].trigger_step = 0;
+
             /* ramp speed */
             if(steppers[i].speed < steppers[i].ramp_to_speed)
                steppers[i].speed++;
@@ -96,8 +99,14 @@ void do_steps(){
             if(steppers[i].speed<0)
                 steppers[i].dir_port->BSRR |= 1 << (steppers[i].dir_pin + 16);
 
-            /* calculate next step time */
-            steppers[i].next_step = timer + (1000/abs(steppers[i].speed)); // should be safe for 1 overflow
+            // avoid division by zero
+            if(steppers[i].speed != 0){
+                /* calculate next step time 
+                 *
+                 * should be safe for 1 overflow; speeds which
+                 * require longer wait times than uint32_max not supported
+                 * */
+                steppers[i].next_step = timer + (1000/abs(steppers[i].speed));
 
                 /* step and count position */
                 steppers[i].step_port->ODR ^= 1 << steppers[i].step_pin;
@@ -106,16 +115,22 @@ void do_steps(){
                 if(steppers[i].speed<0)
                     steppers[i].pos--;
 
+            }
+            else{
+                // dont send step at speed == 0
+                steppers[i].next_step = timer + 1;
+            }
+
             printf("pos %d\tspeed %d\n", steppers[i].pos, steppers[i].speed);
         }
 
         if(steppers[i].homed){
-            int16_t old_ramp_to_speed = steppers[i].ramp_to_speed;
-
+            static uint16_t old_ramp_to_speed;
+            old_ramp_to_speed = steppers[i].ramp_to_speed;
             steppers[i].ramp_to_speed = rxBuffer[1] - steppers[i].pos;
 
-            if(steppers[i].ramp_to_speed != 0 && old_ramp_to_speed == 0)
-                steppers[i].next_step = timer+1;
+            if(old_ramp_to_speed == 0 && steppers[i].ramp_to_speed != 0)
+                steppers[i].trigger_step = 1;
         }
         else{
             if(~(steppers[i].home_port->IDR) & (1 << steppers[i].home_pin)){
@@ -128,7 +143,7 @@ void do_steps(){
             else{
                 if(steppers[i].ramp_to_speed == 0){
                     steppers[i].ramp_to_speed=10;
-                    steppers[i].next_step = timer+1;
+                    steppers[i].trigger_step = 1; // trigger first step
                 }
             }
         }