This example demonstrates how to use the FATFS partition generation tool fatfsgen.py to automatically create a FATFS filesystem image (without wear levelling support) from the contents of a host folder during build, with an option of automatically flashing the created image on invocation of idf.py -p PORT flash. Beware that the minimal required size of the flash is 4 MB. The generated partition does not support wear levelling, so it can be mounted only in read-only mode.

The following gives an overview of the example:

There is a directory fatfs_image from which the FATFS filesystem image will be created.
The function fatfs_create_partition_image is used to specify that a FATFS image should be created during build for the storage partition. For CMake, it is called from the main component's CMakeLists.txt. FLASH_IN_PROJECT specifies that the created image should be flashed on invocation of idf.py -p PORT flash together with app, bootloader, partition table, etc. The image is created on the example's build directory with the output filename storage.bin.
Upon invocation of idf.py -p PORT flash monitor, application loads and finds there is already a valid FATFS filesystem in the storage partition with files same as those in fatfs_image directory. The application is then able to read those files.

How to use example

Build and flash

To run the example, type the following command:

# CMake
idf.py -p PORT flash monitor

(To exit the serial monitor, type Ctrl-].)

See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.

Example output

Here is the example's console output:

...
I (322) example: Mounting FAT filesystem
I (332) example: Reading file
I (332) example: Read from file: 'this is test'
I (332) example: Unmounting FAT filesystem
I (342) example: Done

The logic of the example is contained in a single source file, and it should be relatively simple to match points in its execution with the log outputs above.