@martinnn lib_imu is a library that I wrote and in this function give only data from IMU and there aren't any delay. if I wrote data immediately on a file.txt in SD card it employ 0,2 s so the sample became 0,4. but if I collect data and insert them in a list to save data at the end of acquisition it gives me the error 'Memory allocation'.

@jorismathijssen Hi Joris. Did you tried tot upload thé firmware again? Be sure to powercycle your device. Did you run dfu utils with elevated rights? (Admin on Windows of sudoku on Linux?) Good luck