File Systems

Report
Real-Time Library:
Flash File System
1
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
4-2
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.
4-3
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)
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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“)
4-4
Flash File System - Basics
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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:
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The File system may be used with or without RL-RTX
The file system integrates with RL-TCP
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RL-FlashFS library file
Configuration file File_Config.c
TFTP server
Webserver upload
The File system integrates with RL-USB Mass Storage Class
(MSC)
4-5
Memory Organization
 A Flash device is usually divided
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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
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8-bit (byte)
16-bit (half word)
32-bit (word)
4-6
Memory Organization
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– 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
4-7
RAM Device
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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:
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ARM7 & ARM9: FS_ARM_L.lib
Cortex-M3: FS_CM3.lib
4-8
RAM device
4-9
RAM
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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
4-10
Flash File system functions
4-11
Flash File system functions
4-12
SD CARD
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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
4-13
SD CARD
4-14
Using Memory Cards

Memory cards can be used in
 SPI
mode or
 Native mode
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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()
4-15
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
4-16
SD CARD - MCI MODE

Uses a MCI Driver for low level functions
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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:
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
MCI_LPC23xx.c
4-17

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