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FreeRTOS+FAT is still in the lab
FreeRTOS+FAT is already in use in commercial products and we encourage you to try it yourself. Be aware however that FreeRTOS+FAT was acquired by Real Time Engineers Ltd., and is still being documented and updated to ensure it meets our strict quality standards. Please use the forum for support, or contact us directly if you have a specific business interest.


[FreeRTOS+FAT Native API Reference]

FF_Error_t FF_Format( FF_Disk_t *pxDisk,
                    BaseType_t xPartitionNumber,
                    BaseType_t xPreferFAT16,
                    BaseType_t xSmallClusters );

The media is the physical device on which files are stored. Examples of media suitable for use in an embedded file system include SD cards, solid state disks, NOR flash memory chips, NAND flash chips, and RAM chips.

Media cannot be used to hold a FreeRTOS+FAT file system until it has been partitioned.

Partitioning divides the media into multiple units, each of which is called a partition. Each partition can then be formatted to hold its own file system. A partition can be formatted externally (for example Windows can format an SD-card), or using the FF_Format() function.

FF_Format() will dynamically determine the FAT type and cluster size to use. The cluster size will relate to the cluster count, and the cluster count to the FAT type. The xPreferFAT16 and xSmallClusters parameters allow a preference to be specified. For example, for a small RAM disk set both parameters to true to use FAT16 with small clusters, and for a large SD-card set both parameters to false to use FAT32 with large clusters. Larger clusters can be accessed more quickly, whereas smaller clusters waste less space as they will have fewer unused blocks at the end of a file.


pxDisk   The FF_Disk_t structure that describes the media that contains the partition to be formatted.

xPartitionNumber   The number of the partition on the media to format. Partition numbers start from 0.

xPreferFAT16   Set to pdTRUE to use FAT16 if it is possible, otherwise use FAT32.

xSmallClusters   Set to pdTRUE to use small clusters if it is possible, otherwise use large clusters. When set to pdFALSE, the largest possible cluster size will be selected. The actual size will depends on the FAT type in use.


If the media is successfully formatted then FF_ERR_NONE is returned. If the media could not be formatted then an error code is returned. FF_GetErrMessage() converts error codes into error descriptions.

Example usage:

#define PARTITION_NUMBER        0

static FF_Error_t prvPartitionAndFormatDisk( FF_Disk_t *pxDisk )
FF_PartitionParameters xPartition;
FF_Error_t xError;

    /* Media cannot be used until it has been partitioned.  In this
	case a single partition is to be created that fills all available space - so
	by clearing the xPartition structure to zero. */
    memset( &xPartition, 0x00, sizeof( xPartition ) );
    xPartition.ulSectorCount = pxDisk->ulNumberOfSectors;
    xPartition.ulHiddenSectors = HIDDEN_SECTOR_COUNT;
    xPartition.xPrimaryCount = PRIMARY_PARTITIONS;
    xPartition.eSizeType = eSizeIsQuota;

    /* Perform the partitioning. */
    xError = FF_Partition( pxDisk, &xPartition );

    /* Print out the result of the partition operation. */
    FF_PRINTF( "FF_Partition: FF_Format: %s\n", FF_GetErrMessage( xError ) );

    /* Was the disk partitioned successfully? */
    if( FF_isERR( xError ) == pdFALSE )
        /* The disk was partitioned successfully.  Format the first partition. */
        xError = FF_Format( pxDisk, ramPARTITION_NUMBER, pdTRUE, pdTRUE );

        /* Print out the result of the format operation. */
        FF_PRINTF( "FF_RAMDiskInit: FF_Format: %s\n", FF_GetErrMessage( xError ) );

    return xError;
Using the FF_Partition() and FF_Format() functions to partition the disk, then format a partition

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