203 lines
7.8 KiB
C
203 lines
7.8 KiB
C
/* Arduino SdFat Library
|
|
* Copyright (C) 2009 by William Greiman
|
|
*
|
|
* This file is part of the Arduino SdFat Library
|
|
*
|
|
* This Library is free software: you can redistribute it and/or modify
|
|
* it under the terms of the GNU General Public License as published by
|
|
* the Free Software Foundation, either version 3 of the License, or
|
|
* (at your option) any later version.
|
|
*
|
|
* This Library is distributed in the hope that it will be useful,
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
* GNU General Public License for more details.
|
|
*
|
|
* You should have received a copy of the GNU General Public License
|
|
* along with the Arduino SdFat Library. If not, see
|
|
* <http://www.gnu.org/licenses/>.
|
|
*/
|
|
|
|
/**
|
|
\mainpage Arduino SdFat Library
|
|
<CENTER>Copyright © 2009 by William Greiman
|
|
</CENTER>
|
|
|
|
\section Intro Introduction
|
|
The Arduino SdFat Library is a minimal implementation of FAT16 and FAT32
|
|
file systems on SD flash memory cards. Standard SD and high capacity
|
|
SDHC cards are supported.
|
|
|
|
The SdFat only supports short 8.3 names.
|
|
|
|
The main classes in SdFat are Sd2Card, SdVolume, and SdFile.
|
|
|
|
The Sd2Card class supports access to standard SD cards and SDHC cards. Most
|
|
applications will only need to call the Sd2Card::init() member function.
|
|
|
|
The SdVolume class supports FAT16 and FAT32 partitions. Most applications
|
|
will only need to call the SdVolume::init() member function.
|
|
|
|
The SdFile class provides file access functions such as open(), read(),
|
|
remove(), write(), close() and sync(). This class supports access to the root
|
|
directory and subdirectories.
|
|
|
|
A number of example are provided in the SdFat/examples folder. These were
|
|
developed to test SdFat and illustrate its use.
|
|
|
|
SdFat was developed for high speed data recording. SdFat was used to implement
|
|
an audio record/play class, WaveRP, for the Adafruit Wave Shield. This
|
|
application uses special Sd2Card calls to write to contiguous files in raw mode.
|
|
These functions reduce write latency so that audio can be recorded with the
|
|
small amount of RAM in the Arduino.
|
|
|
|
\section SDcard SD\SDHC Cards
|
|
|
|
Arduinos access SD cards using the cards SPI protocol. PCs, Macs, and
|
|
most consumer devices use the 4-bit parallel SD protocol. A card that
|
|
functions well on A PC or Mac may not work well on the Arduino.
|
|
|
|
Most cards have good SPI read performance but cards vary widely in SPI
|
|
write performance. Write performance is limited by how efficiently the
|
|
card manages internal erase/remapping operations. The Arduino cannot
|
|
optimize writes to reduce erase operations because of its limit RAM.
|
|
|
|
SanDisk cards generally have good write performance. They seem to have
|
|
more internal RAM buffering than other cards and therefore can limit
|
|
the number of flash erase operations that the Arduino forces due to its
|
|
limited RAM.
|
|
|
|
\section Hardware Hardware Configuration
|
|
|
|
SdFat was developed using an
|
|
<A HREF = "http://www.adafruit.com/"> Adafruit Industries</A>
|
|
<A HREF = "http://www.ladyada.net/make/waveshield/"> Wave Shield</A>.
|
|
|
|
The hardware interface to the SD card should not use a resistor based level
|
|
shifter. SdFat sets the SPI bus frequency to 8 MHz which results in signal
|
|
rise times that are too slow for the edge detectors in many newer SD card
|
|
controllers when resistor voltage dividers are used.
|
|
|
|
The 5 to 3.3 V level shifter for 5 V Arduinos should be IC based like the
|
|
74HC4050N based circuit shown in the file SdLevel.png. The Adafruit Wave Shield
|
|
uses a 74AHC125N. Gravitech sells SD and MicroSD Card Adapters based on the
|
|
74LCX245.
|
|
|
|
If you are using a resistor based level shifter and are having problems try
|
|
setting the SPI bus frequency to 4 MHz. This can be done by using
|
|
card.init(SPI_HALF_SPEED) to initialize the SD card.
|
|
|
|
\section comment Bugs and Comments
|
|
|
|
If you wish to report bugs or have comments, send email to fat16lib@sbcglobal.net.
|
|
|
|
\section SdFatClass SdFat Usage
|
|
|
|
SdFat uses a slightly restricted form of short names.
|
|
Only printable ASCII characters are supported. No characters with code point
|
|
values greater than 127 are allowed. Space is not allowed even though space
|
|
was allowed in the API of early versions of DOS.
|
|
|
|
Short names are limited to 8 characters followed by an optional period (.)
|
|
and extension of up to 3 characters. The characters may be any combination
|
|
of letters and digits. The following special characters are also allowed:
|
|
|
|
$ % ' - _ @ ~ ` ! ( ) { } ^ # &
|
|
|
|
Short names are always converted to upper case and their original case
|
|
value is lost.
|
|
|
|
\note
|
|
The Arduino Print class uses character
|
|
at a time writes so it was necessary to use a \link SdFile::sync() sync() \endlink
|
|
function to control when data is written to the SD card.
|
|
|
|
\par
|
|
An application which writes to a file using \link Print::print() print()\endlink,
|
|
\link Print::println() println() \endlink
|
|
or \link SdFile::write write() \endlink must call \link SdFile::sync() sync() \endlink
|
|
at the appropriate time to force data and directory information to be written
|
|
to the SD Card. Data and directory information are also written to the SD card
|
|
when \link SdFile::close() close() \endlink is called.
|
|
|
|
\par
|
|
Applications must use care calling \link SdFile::sync() sync() \endlink
|
|
since 2048 bytes of I/O is required to update file and
|
|
directory information. This includes writing the current data block, reading
|
|
the block that contains the directory entry for update, writing the directory
|
|
block back and reading back the current data block.
|
|
|
|
It is possible to open a file with two or more instances of SdFile. A file may
|
|
be corrupted if data is written to the file by more than one instance of SdFile.
|
|
|
|
\section HowTo How to format SD Cards as FAT Volumes
|
|
|
|
You should use a freshly formatted SD card for best performance. FAT
|
|
file systems become slower if many files have been created and deleted.
|
|
This is because the directory entry for a deleted file is marked as deleted,
|
|
but is not deleted. When a new file is created, these entries must be scanned
|
|
before creating the file, a flaw in the FAT design. Also files can become
|
|
fragmented which causes reads and writes to be slower.
|
|
|
|
Microsoft operating systems support removable media formatted with a
|
|
Master Boot Record, MBR, or formatted as a super floppy with a FAT Boot Sector
|
|
in block zero.
|
|
|
|
Microsoft operating systems expect MBR formatted removable media
|
|
to have only one partition. The first partition should be used.
|
|
|
|
Microsoft operating systems do not support partitioning SD flash cards.
|
|
If you erase an SD card with a program like KillDisk, Most versions of
|
|
Windows will format the card as a super floppy.
|
|
|
|
The best way to restore an SD card's format is to use SDFormatter
|
|
which can be downloaded from:
|
|
|
|
http://www.sdcard.org/consumers/formatter/
|
|
|
|
SDFormatter aligns flash erase boundaries with file
|
|
system structures which reduces write latency and file system overhead.
|
|
|
|
SDFormatter does not have an option for FAT type so it may format
|
|
small cards as FAT12.
|
|
|
|
After the MBR is restored by SDFormatter you may need to reformat small
|
|
cards that have been formatted FAT12 to force the volume type to be FAT16.
|
|
|
|
If you reformat the SD card with an OS utility, choose a cluster size that
|
|
will result in:
|
|
|
|
4084 < CountOfClusters && CountOfClusters < 65525
|
|
|
|
The volume will then be FAT16.
|
|
|
|
If you are formatting an SD card on OS X or Linux, be sure to use the first
|
|
partition. Format this partition with a cluster count in above range.
|
|
|
|
\section References References
|
|
|
|
Adafruit Industries:
|
|
|
|
http://www.adafruit.com/
|
|
|
|
http://www.ladyada.net/make/waveshield/
|
|
|
|
The Arduino site:
|
|
|
|
http://www.arduino.cc/
|
|
|
|
For more information about FAT file systems see:
|
|
|
|
http://www.microsoft.com/whdc/system/platform/firmware/fatgen.mspx
|
|
|
|
For information about using SD cards as SPI devices see:
|
|
|
|
http://www.sdcard.org/developers/tech/sdcard/pls/Simplified_Physical_Layer_Spec.pdf
|
|
|
|
The ATmega328 datasheet:
|
|
|
|
http://www.atmel.com/dyn/resources/prod_documents/doc8161.pdf
|
|
|
|
|
|
*/
|