Real-Time Library: Flash File System

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Flash File System - Basics

– The RL-FlashFS allows to create, save, read and modify files – The library functions provide high level access to file system functionalities – Usage with the MicroLib runtime library is not supported

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What is MicroLib

 MicroLib is a highly-optimized library for ARM-based embedded applications written in C. When compared to the standard C library included with the ARM Compilation Tools, MicroLib provides significant code size advantages required for many embedded systems .

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Flash File System - Basics

 Supported memory devices:  External RAM  External Flash (SPI)  Internal Flash  Memory Cards like SD and MMC cards (used in SPI mode)  Default drives:  “R:“ external RAM (“Ram Drive“)  “S:“ external Flash (“SPI Flash device“)  “F:“ internal Flash (“Embedded Flash drive“)  “M:“ external Memory Cards (“Memory Card Drive“)

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Flash File System - Basics

       Up to 4 GByte memory space is supported Supported file system for memorycards are FAT16 or FAT32 All devices can be used parallel Required components:  RL-FlashFS library file  Configuration file File_Config.c

The File system may be used with or without RL-RTX The file system integrates with RL-TCP  TFTP server  Webserver upload The File system integrates with RL-USB Mass Storage Class (MSC)

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Memory Organization

   A Flash device is usually divided into flash sectors (Block) – A Flash sector is a memory page which is written cell after cell – The size of a memory cell depends on device architecture  8-bit (byte)  16-bit (half word)  32-bit (word)

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Memory Organization

  – A big file is separated into multiple blocks – Smaller files are stored together in one block  Deleting a file:  The whole flash sector has to be erased  Data within this sector which is not to be deleted will be saved within another sector  Changing a file:  Changed data is stored into a new sector  The file pointer is actualized  The sector with the old file data is erased

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RAM Device

    Configuring the file system to use the internal RAM of a typical ARM based microcontroller.

Not practical in real life - RAM is volatile (unless battery backed) Basic Configuration file:

File_Config.c

Libraries:  ARM7 & ARM9:

FS_ARM_L.lib

 Cortex-M3:

FS_CM3.lib

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RAM device

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RAM

     RAM Device has to be split into

logical sectors

– Usage without Device Description Table – Device layout is generated automatically by configuration (

File_Config.c)

– RAM devices need special low-level read/write function – High-level handling is equal to Flash devices

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Flash File system functions

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Flash File system functions

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SD CARD

 Hardware Wear levelling and error correction  Giga bytes of low cost storage  100Mbit/sec data transfer rate  Write protection  Optional copyright protection  Standard communication protocol  Independent from the underlying flash technology  Typically 100K Writes endurance  Low cost

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SD CARD

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Using Memory Cards

 Memory cards can be used in  SPI mode or  Native mode  Uses the FAT file system Supports no directories or subdirectories  Maximum of 512 directory entries  File Information Record of each file stores time information too  fs_get_time()  fs_get_date()

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SD CARD SPI MODE

 Uses a SPI Driver for low level functions  -

spi_init() Initialize the SPI controller



spi hi speed() Change between high and low SPI mode spi_hi_speed for SPI data transfer



spi_send() Writes and reads a byte on the SPI

interface

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SD CARD - MCI MODE

  Uses a MCI Driver for low level functions 

mci_init() Initialize the MCI controller



mci_read_sect() Reads a sector from the Flash

Memory Card (512 byte) 

mci_write_sect() Write a sector to the Flash Memory

Card (512 byte) 

mci_read_config() Reads Memory Card configuration

Memory Card is handled in hardware Communication in Native mode is faster than in SPI mode  – MCI Driver:  MCI_LPC23xx.c

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