float accX = 0.0F;
float accY = 0.0F;
float accZ = 0.0F;
float zeit = 0.0F;
float testX = 0.0F;
char msg[100];
unsigned long zeit_start = 0.0;
unsigned long zeit_end = 0.0;
boolean button_a = false;
boolean measurement = false;
boolean start = true;

void writeFile(fs::FS &fs, const char * path, const char * message){
Serial.printf("Writing file: %s\n", path);

File file = fs.open(path, FILE_WRITE);
if(!file){
    Serial.println("Failed to open file for writing");
    return;
}
if(file.print(message)){
    Serial.println("File written");
} else {
    Serial.println("Write failed");
}
file.close();

}
void appendFile(fs::FS &fs, const char * path, const char * message){
Serial.printf("Appending to file: %s\n", path);

File file = fs.open(path, FILE_APPEND);
if(!file){
    Serial.println("Failed to open file for appending");
    return;
}
if(file.print(message)){
    Serial.println("Message appended");
} else {
    Serial.println("Append failed");
}
file.close();

}
void readFile(fs::FS &fs, const char * path){
Serial.printf("Reading file: %s\n", path);
File file = fs.open(path);
if(!file){
Serial.println("Failed to open file for reading");
return;
}
Serial.print("Read from file:\n ");
while(file.available()){
Serial.write(file.read());
testX = testX + (abs(accX));
}
file.close();
}
void setup() {
M5.begin();
M5.Power.begin();
M5.IMU.Init();
M5.Lcd.println("Press button A to\nstart measurement");

Serial.begin(115200);
if(!SD.begin()){
Serial.println("Card Mount Failed");
return;
}
uint8_t cardType = SD.cardType();

if(cardType == CARD_NONE){
    Serial.println("No SD card attached");
    return;
}

Serial.print("SD Card Type: ");
if(cardType == CARD_MMC){
    Serial.println("MMC");
} else if(cardType == CARD_SD){
    Serial.println("SDSC");
} else if(cardType == CARD_SDHC){
    Serial.println("SDHC");
} else {
    Serial.println("UNKNOWN");
}
writeFile(SD, "/acceleration.txt", "   Time    aX       aY        aZ");

while (start){

 zeit_start = millis();
 if (M5.BtnA.wasReleasefor(70))
     {
         button_a = (!(button_a));
         measurement = (!(measurement));
      } 
  if (button_a)
  {
    while (measurement)
      {
          zeit_end = millis()-zeit_start;
          M5.IMU.getAccelData(&accX,&accY,&accZ);

          snprintf(msg, 100, "\r\n  %5.2lf   %5.2lf     %5.2lf     %5.2lf",zeit, accX, accY, accZ);    // => Daten lesen mit sscanf?????
          appendFile(SD, "/acceleration.txt", msg);

          if (M5.BtnA.wasReleasefor(70))
             {
                button_a = (!(button_a));
                measurement = (!(measurement));
                M5.Lcd.println("Press button A to\nstart measurement");

                readFile(SD, "/acceleration.txt");
                Serial.println(" ");
                Serial.println(testX);
             }
      }
  }

}
}