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3. Write a program in internal file system

3.1. Internal file system

The FAT file system is created and initialized in the RA MCU’s internal flash when the MicroPython starts at the first time on the board. The file system is mounted as “/flash”, so you can access this flash system and create a program file into the /flash directory.

As the factory setting, following size is allocated for the file system:

Board	File System Size
EK-RA4M1	36KB ( 36864B)
EK-RA4W1	64KB ( 65536B)
EK-RA6M1	64KB ( 65536B)
EK-RA6M2	128KB (131072B)
RA4M1 CLICKER	36KB ( 36864B)

As the factory setting, following 2 files are created in the file system:

• boot.py : executed first when the system starts

• main.py : executed after boot.py completes

See Reset and Boot Sequence for more information.

3.2. Write a program in the internal file system

You can write a program in main.py which is executed automatically when the MicroPython starts. For example, you can write LED blinking program like below:

import os
os.getcwd()
f = open('main.py', 'rw+')
print(f.read())
f.write('import time\n')
f.write('from machine import Pin\n')
f.write('led1 = Pin(Pin.cpu.P106)\n')
f.write('while True:\n')
f.write('    led1.on()\n')
f.write('    time.sleep(1)\n')
f.write('    led1.off()\n')
f.write('    time.sleep(1)\n')
f.close()
f = open('main.py', 'r')
print(f.read())
f.close()

Entering CTRL-D for software reset, the MicroPython reboots, displays following messages:

MPY: sync filesystems
MPY: soft reboot

and main.py is executed and LED1 blinks per 1 second. If you want to stop the program, please enter CTRL-C.