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For many IoT devices, having a small and flexible file system is essential.

There are not many file systems running on the MCU. Most people should be aware of the FatFS file system. Today I will tell you about the contents of FatFS and LittleFS, and some of the differences between them.

One, the file system FatFS

FatFs is a universal file system (FAT/exFAT) module used to implement FAT file system in small embedded systems.

URL:

http://elm-chan.org/fsw/ff/00index_e.html

 

The writing of FatFs components follows ANSI C (C89) and is completely separated from the disk I/O layer, so it does not depend on the hardware platform. It can be embedded in microcontrollers with limited resources, such as 8051, PIC, AVR, ARM, Z80, RX, etc., without any modification.

---From Baidu Encyclopedia

feature

a.DOS/Windows compatible FAT/exFAT file system.

b. Platform is independent and easy to transplant.

c. The space occupied by the program code and work area is very small.

d. Support the following various configuration options:

• Long file name in ANSI/OEM or Unicode.

• The exFAT file system, 64-bit LBA and GPT can store large amounts of data.

• Thread safety of RTOS.

• Multiple volumes (physical drives and partitions).

• Variable sector size.

• Multiple code pages, including DBCS.

• Read only, optional API, I/O buffer, etc...

If you know how to use STM32CubeMX, it is very easy to use FatFS. You can "turn" STM32 into a USB flash drive in a few easy steps.

Second, the file system Littlefs

There are relatively few people who know the Littlefs file system, but most people who have used the Mbed OS system should know.

Mbed OS is a set of free, open-source and open-source embedded operating systems developed by Arm for the Cortex-M series of processors for IoT, specifically designed for the "things" in the Internet of Things.

And Littlefs justPart of the content of Mbed is as follows:

Source address:

https://github.com/armmbed/mbed-littlefs

Littlefs features:

• Small resource occupation: IoT devices are limited by ROM and RAM.

• Power failure recovery capability: The file system is required to be consistent and refresh data to the underlying storage.

• Average wear and tear: Generally, storage supports a limited number of erases per block, so using the entire storage device is very important for reliability.

The usage is also quite simple, see the official routine:

#include "LittleFileSystem2.h"
#include "SPIFBlockDevice.h"


// Physical block device, can be any device that supports the BlockDevice API
SPIFBlockDevice bd(PTE2, PTE4, PTE1, PTE5);


// Storage for the littlefs
LittleFileSystem2 fs("fs");


// Entry point
int main() {
    // Mount the filesystem
    int err = fs.mount(&bd);
    if (err) {
        // Reformat if we can't mount the filesystem,
        // this should only happen on the first boot
        LittleFileSystem2::format(&bd);
        fs.mount(&bd);
    }


    // Read the boot count
    uint32_t boot_count = 0;
    FILE *f = fopen("/fs/boot_count", "r+");
    if (!f) {
        // Create the file if it doesn't exist
        f = fopen("/fs/boot_count", "w+");
    }
    fread(&boot_count, sizeof(boot_count), 1, f);


    // Update the boot count
    boot_count += 1;
    rewind(f);
    fwrite(&boot_count, sizeof(boot_count), 1, f);


    // Remember that storage may not be updated until the file
    // is closed successfully
    fclose(f);


    // Release any resources we were using
    fs.unmount();


    // Print the boot count
    printf("boot_count: %ld\n", boot_count);
}

Three, file system comparison

Every product has its value,The same is true for file systems, each with its own advantages and disadvantages. Here are a few simple differences between them.

1. Resource RAM/ROM size

Littlefs is a high integrity embedded file system in Mbed OS, optimized for use with MCUs with limited RAM and ROM.

LittlefsThe highly integrated embedded file system uses 13K ROM less than FAT and less than 4K RAM.

2. Power loss recovery ability

Littlefs has a strong copy-on-write guarantee, and the storage on the disk is always kept in a valid state. A system that may have random power failures is suitable for this file system.

3. Wear leveling

Most memory chips used in embedded devices support a limited erase set per sector. If there is no equalization, the life of the embedded device may be affected.

Reference source:

https://os.mbed.com/blog/entry/littlefs-high-integrity-embedded-fs/

Disclaimer: The source network of this article, the copyright belongs to the original author. If the copyright issue of the work is involved, please contact me to delete it.
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