LittleFS on bare metal

Mbed OS
1

Should LittleFS work on bare metal (without RTOS)? I tried to compile a program using LittleFS on SPIF with { "requires": ["bare-metal"] }, but the compiler was unable to find the header file.

2

It worked for us on a uBlox Nina B3 ( Nordic chip ). Here’s our mbed app json:

{
  "requires": [ "bare-metal", "nordic" ],
  "target_overrides": {
    "NRF52840_DK": {
      "target.features_remove": [ "CRYPTOCELL310" ]
    }

And here’s the littleFS instantiation:

#include "SPIFBlockDevice.h"
using namespace mbed;

SPIFBlockDevice flash_bd(MBED_CONF_SPIF_DRIVER_SPI_MOSI, 
                        MBED_CONF_SPIF_DRIVER_SPI_MISO, 
                        MBED_CONF_SPIF_DRIVER_SPI_CLK, 
                        MBED_CONF_SPIF_DRIVER_SPI_CS, 
                        MBED_CONF_SPIF_DRIVER_SPI_FREQ);

#include "lfs.h"
#include "FlashIAP.h"

// variables used by the filesystem
lfs_t lfs;
lfs_file_t file;
FlashIAP internal_flash;

//function prototypes
static void lfs_bd_init(lfs_config* cfg);
static int lfs_bd_read(const struct lfs_config *c, lfs_block_t block,
                       lfs_off_t off, void *buffer, lfs_size_t size);
static int lfs_bd_prog(const struct lfs_config *c, lfs_block_t block,
                       lfs_off_t off, const void *buffer, lfs_size_t size);
static int lfs_bd_erase(const struct lfs_config *c, lfs_block_t block);
static int lfs_bd_sync(const struct lfs_config *c);

// configuration of the filesystem is provided by this struct
struct lfs_config cfg = {
    // block device operations
    .context = &flash_bd,
    .read  = lfs_bd_read,
    .prog  = lfs_bd_prog,
    .erase = lfs_bd_erase,
    .sync  = lfs_bd_sync,
};
  }
}

I also found this file compiled in ( I didn’t write the code )

#include "lfs.h"
#include "lfs_util.h"
#include "MbedCRC.h"

namespace mbed {

//Copied from LittleFileSystem.cpp. Couldn't use the default version since it is
//gaurded by preprocessors #ifndef that are needed for other processes, and
//including the LittleFileSystem.h and LittleFileSystem.cpp would require a
//large amount of overhead just for this function. As per ARM mbed documentation
//this function is intended to be replaced by custom code if desired, so this
//makes it more reasonable to copy from known source.
extern "C" void lfs_crc(uint32_t *crc, const void *buffer, size_t size)
{
    uint32_t initial_xor = *crc;
    MbedCRC<POLY_32BIT_REV_ANSI, 32> ct(initial_xor, 0x0, true, false);
    ct.compute((void *)buffer, size, (uint32_t *) crc);
}

} //namespace mbed