diff --git a/PSE-firmware b/PSE-firmware
index bf08fc6..8a099f5 160000
--- a/PSE-firmware
+++ b/PSE-firmware
@@ -1 +1 @@
-Subproject commit bf08fc69ff21c28482ade1eca086867e619b7fea
+Subproject commit 8a099f5c215424ff34ceafaaa35615ec0fbeb685
diff --git a/fatfs.c b/fatfs.c
index 9967001..107a894 100644
--- a/fatfs.c
+++ b/fatfs.c
@@ -1,5 +1,6 @@
 #include "fatfs.h"
 
+#include <errno.h>
 #include <stdio.h>
 
 FRESULT f_open (
@@ -7,8 +8,21 @@ FRESULT f_open (
 	const TCHAR* path,	/* Pointer to the file name */
 	BYTE mode			/* Access mode and file open mode flags */
 ){
-  printf("file open try\n");
-  return FR_NO_FILE;
+	FILE* f;
+	printf("mode %d\n", mode);
+	if(mode & FA_READ)
+		f = fopen(path, "r");
+	else if(mode & FA_WRITE && mode & FA_OPEN_ALWAYS)
+		f = fopen(path, "w+");
+	else
+		printf("Unimplemented mode");
+	if(f == NULL){
+		printf("errno %d\n",errno);
+		return FR_NO_FILE;
+	}
+	*fp = f;
+
+  return FR_OK;
 }
 
 FRESULT f_read (
@@ -17,15 +31,15 @@ FRESULT f_read (
 	UINT btr,		/* Number of bytes to read */
 	UINT* br		/* Pointer to number of bytes read */
 ){
-  printf("file read try\n");
-  return FR_NO_FILE;
+	*br = fread(buff, 1, btr, *fp);
+  return FR_OK;
 }
 
 FRESULT f_close (
 	FIL *fp		/* Pointer to the file object to be closed */
 ){
-  printf("file close try\n");
-  return FR_NO_FILE;
+	fclose(*fp);
+  return FR_OK;
 }
 
 FRESULT f_write (
@@ -34,6 +48,6 @@ FRESULT f_write (
 	UINT btw,			/* Number of bytes to write */
 	UINT* bw			/* Pointer to number of bytes written */
 ){
-  printf("file write try\n");
-  return FR_NO_FILE;
+	*bw = fwrite(buff, 1, btw, *fp);
+  return FR_OK;
 }
diff --git a/fatfs.h b/fatfs.h
index 4113ab5..d5f391d 100644
--- a/fatfs.h
+++ b/fatfs.h
@@ -1,5 +1,6 @@
-typedef struct {
-} FIL;
+#include <stdio.h>
+
+typedef FILE* FIL;
 
 typedef enum {
 	FR_OK = 0,				/* (0) Succeeded */
diff --git a/main.c b/main.c
index e61d4bf..b73969a 100644
--- a/main.c
+++ b/main.c
@@ -32,6 +32,7 @@ TIM_HandleTypeDef htim5;
 pse_unit pse_units[PSE_UNITS_NUM];
 pse_syringe pse_syringes[PSE_UNITS_NUM];
 pse_home_display pse_home_displays[PSE_UNITS_NUM];
+pse_stepper_status pse_steppers_status[PSE_UNITS_NUM];
 
 enum steppers_axis{PSE_X_STEPPER, PSE_Y_STEPPER, PSE_Z_STEPPER, PSE_E_STEPPER, PSE_STEPPER_NUM};
 pse_stepper_conf pse_stepper_confs[PSE_STEPPER_NUM] = {
@@ -120,7 +121,7 @@ int main(int argc, char** argv){
   lv_label_set_text(cursor, "A");
   lv_indev_set_cursor(my_indev, cursor);
 
-  load_units(pse_units, pse_syringes, pse_stepper_confs, pse_home_displays, PSE_UNITS_NUM, 0);
+  load_units(pse_units, pse_syringes, pse_stepper_confs, pse_steppers_status, pse_home_displays, PSE_UNITS_NUM, 0);
   Home_Screen_Gen(pse_units, PSE_UNITS_NUM, false);
 
   pthread_t tickThread;
diff --git a/stm32f1xx_hal.c b/stm32f1xx_hal.c
index af71b1d..6bbfdaa 100644
--- a/stm32f1xx_hal.c
+++ b/stm32f1xx_hal.c
@@ -47,7 +47,7 @@ static void* tim_handler(void* arg){
     int backlog = nb_exec - exec_counter;
     if(backlog > 10)
       printf("timer simulation lagging behind (%d ticks)\n", backlog);
-    while(backlog > 0){  
+    while(backlog > 0 && htim->started){
       HAL_TIM_PeriodElapsedCallback(htim);
       exec_counter++;
       backlog = nb_exec - exec_counter;
diff --git a/stm32f1xx_hal.h b/stm32f1xx_hal.h
index d3f367b..e0deb96 100644
--- a/stm32f1xx_hal.h
+++ b/stm32f1xx_hal.h
@@ -10,7 +10,7 @@ typedef struct {
 typedef struct{
   uint16_t presc;
   uint16_t period;
-  uint8_t started;
+  volatile uint8_t started;
 } TIM_HandleTypeDef;
 typedef int HAL_StatusTypeDef;