diff --git a/Core/Inc/PSE_unit.h b/Core/Inc/PSE_unit.h
index 61b4989..5e192b2 100644
--- a/Core/Inc/PSE_unit.h
+++ b/Core/Inc/PSE_unit.h
@@ -22,6 +22,7 @@ typedef enum {PORT_X, PORT_Y, PORT_Z, PORT_E} pse_ports;
 typedef struct{
   uint32_t step_itvl;
   uint8_t step_max;
+  uint32_t tick_counter;
 
   GPIO_TypeDef* EN_GPIO_Port;
   uint16_t EN_GPIO_Pin;
diff --git a/Core/Inc/pse_stepper_planer.h b/Core/Inc/pse_stepper_planer.h
index d9227c2..28c479c 100644
--- a/Core/Inc/pse_stepper_planer.h
+++ b/Core/Inc/pse_stepper_planer.h
@@ -10,11 +10,18 @@
 
 #include "PSE_unit.h"
 
+#define PSE_STEPPER_INTERRUPT_RATE 20000 // 64Mhz (Presc 64, count 50) : 20kHz
+#define PSE_STEPPER_SCREW_PITCH 1000 // M6 : 1000µm / rotation
+#define PSE_STEPPER_STEPS_PER_ROTATION 200 // NEMA17 without microstepping 200 steps/rotation
+
 void pse_sp_start_axis(pse_stepper_conf* conf);
 void pse_sp_stop_axis(pse_stepper_conf* conf);
 void pse_sp_set_dir(pse_stepper_conf* conf, int dir);
 void pse_stepper_planer_tick(pse_unit* units, uint8_t units_num);
 
-unsigned int get_tick_counter();
+void pse_sp_start_all(pse_unit* units, int unit_num);
+void pse_sp_stop_all(pse_unit* units, int unit_num);
+
+void pse_stepper_planer_compute_sps(pse_unit* unit);
 
 #endif /* INC_PSE_STEPPER_PLANER_H_ */
diff --git a/Core/Src/PSE_unit.c b/Core/Src/PSE_unit.c
index f4c5f90..e0ff0c5 100644
--- a/Core/Src/PSE_unit.c
+++ b/Core/Src/PSE_unit.c
@@ -19,5 +19,9 @@ void load_units(pse_unit* units, pse_syringe* syringes, pse_stepper_conf* steppe
       .syringe = &syringes[i],
 	  .stepper_conf = &stepper_confs[i],
     };
+    syringes[i] = (pse_syringe){
+    	.name = "Test",
+    	.diameter = 26700,
+    };
   }
 }
diff --git a/Core/Src/PSE_unit_edit_screen.c b/Core/Src/PSE_unit_edit_screen.c
index 4c585d9..e2ca529 100644
--- a/Core/Src/PSE_unit_edit_screen.c
+++ b/Core/Src/PSE_unit_edit_screen.c
@@ -19,12 +19,17 @@
 
 static lv_obj_t* parent_screen;
 static lv_obj_t* this_screen;
+static pse_unit* c_pse_unit;
 
 static void back_button_handler(lv_event_t * e){
   lv_event_code_t code = lv_event_get_code(e);
 
 	if(code == LV_EVENT_CLICKED) {
     // Save
+		// update stepper pwm generation
+		pse_stepper_planer_compute_sps(c_pse_unit);
+
+		// go back to the main menu
 		lv_obj_t* curr_scr = lv_scr_act();
 		lv_scr_load(parent_screen);
 		lv_obj_del(curr_scr);
@@ -192,6 +197,8 @@ void PSE_unit_edit_screen_Gen(lv_obj_t* parent, pse_unit* unit){
 	lv_obj_t* scr = lv_obj_create(NULL);
 	this_screen = scr;
 
+	c_pse_unit = unit;
+
 	// create the top menu on the top 20%
 	lv_obj_t* top_menu = lv_obj_create(scr);
 	lv_obj_set_align(top_menu, LV_ALIGN_TOP_LEFT);
diff --git a/Core/Src/home_screen.c b/Core/Src/home_screen.c
index e9e3411..6428e80 100644
--- a/Core/Src/home_screen.c
+++ b/Core/Src/home_screen.c
@@ -12,6 +12,10 @@
 
 #include "PSE_unit.h"
 #include "PSE_unit_edit_screen.h"
+#include "pse_stepper_planer.h"
+
+static pse_unit* units;
+static int units_num;
 
 static void run_handler(lv_event_t * e){
 	lv_event_code_t code = lv_event_get_code(e);
@@ -22,9 +26,11 @@ static void run_handler(lv_event_t * e){
 		lv_state_t state = lv_obj_get_state(button);
 		if(state & LV_STATE_CHECKED){
 			lv_label_set_text(label, LV_SYMBOL_PAUSE);
+			pse_sp_start_all(units, units_num);
 		}
 		else{
 			lv_label_set_text(label, LV_SYMBOL_PLAY);
+			pse_sp_stop_all(units, units_num);
 		}
   }
 }
@@ -107,6 +113,10 @@ void Home_Screen_Gen(pse_unit* pse_units, uint8_t pse_unit_num){
 	lv_obj_t* scr = lv_obj_create(NULL);
 	screen = scr;
 
+	// set global unit variable
+	units = pse_units;
+	units_num = pse_unit_num;
+
 	// create the top menu on the top 20%
 	lv_obj_t* top_menu = lv_obj_create(scr);
 	lv_obj_set_align(top_menu, LV_ALIGN_TOP_LEFT);
diff --git a/Core/Src/pse_stepper_planer.c b/Core/Src/pse_stepper_planer.c
index c0cc678..a60b828 100644
--- a/Core/Src/pse_stepper_planer.c
+++ b/Core/Src/pse_stepper_planer.c
@@ -9,7 +9,7 @@
 
 #include "PSE_unit.h"
 
-unsigned int tick_counter = 0;
+#include "pse_stepper_planer.h"
 
 void pse_stepper_planer_tick(pse_unit* units, uint8_t units_num){
 	for(int i = 0; i < units_num; i++){
@@ -17,19 +17,16 @@ void pse_stepper_planer_tick(pse_unit* units, uint8_t units_num){
 
 		int state;
 		if(c->step_max){
-			state = tick_counter % 2;
+			c->tick_counter %= 2;
+			state = c->tick_counter;
 		}
 		else{
-			state = (tick_counter % c->step_itvl) == 0;
+			c->tick_counter %= c->step_itvl;
+			state = c->tick_counter == 0;
 		}
-		HAL_GPIO_WritePin(c->STEP_GPIO_Port, c->STEP_GPIO_Pin, tick_counter%2);
+		c->tick_counter++;
+		HAL_GPIO_WritePin(c->STEP_GPIO_Port, c->STEP_GPIO_Pin, state);
 	}
-
-	tick_counter++;
-}
-
-unsigned int get_tick_counter(){
-	return tick_counter;
 }
 
 void pse_sp_start_axis(pse_stepper_conf* conf){
@@ -42,3 +39,26 @@ void pse_sp_stop_axis(pse_stepper_conf* conf){
 void pse_sp_set_dir(pse_stepper_conf* conf, int dir){
 	HAL_GPIO_WritePin(conf->DIR_GPIO_Port, conf->DIR_GPIO_Pin, dir);
 }
+
+
+void pse_stepper_planer_compute_sps(pse_unit* unit){
+	pse_stepper_conf* c = unit->stepper_conf;
+	// magic constants are used to approximate pi and other multiplicatives constant as a rationnal
+	uint64_t numerator = (uint64_t)1 * unit->syringe->diameter * unit->syringe->diameter * PSE_STEPPER_INTERRUPT_RATE * PSE_STEPPER_SCREW_PITCH;
+	uint64_t denominator = (uint64_t)21220209 * unit->flow * PSE_STEPPER_STEPS_PER_ROTATION;
+	c->step_itvl = numerator / denominator;
+}
+
+
+void pse_sp_start_all(pse_unit* units, int units_num){
+	for(int i = 0; i < units_num; i++){
+		if(units[i].enabled)
+			pse_sp_start_axis(units[i].stepper_conf);
+	}
+}
+void pse_sp_stop_all(pse_unit* units, int units_num){
+	for(int i = 0; i < units_num; i++){
+		if(units[i].enabled)
+			pse_sp_stop_axis(units[i].stepper_conf);
+	}
+}