SD Card File System

Table of Contents

  1. Hello World!
  2. Library
  3. Details
  4. Reference

A library to allow SD Cards to be accessed as a filesystem, using a SPI interface.

This library supports:

  • FAT12 / FAT16 / FAT32
  • SD / SDHC cards up to 32Gb
  • long filenames
  • time stamp

Hello World!

» Import this program
SDFileSystem_HelloWorld - main.cpp

#include "mbed.h"
#include "SDFileSystem.h"
 
SDFileSystem sd(p5, p6, p7, p8, "sd"); // the pinout on the mbed Cool Components workshop board
 
int main() {
    printf("Hello World!\n");   
 
    mkdir("/sd/mydir", 0777);
    
    FILE *fp = fopen("/sd/mydir/sdtest.txt", "w");
    if(fp == NULL) {
        error("Could not open file for write\n");
    }
    fprintf(fp, "Hello fun SD Card World!");
    fclose(fp); 
 
    printf("Goodbye World!\n");
}

Library

The SDFileSystem library, for accessing SD Cards using fopen, fprintf, etc.

» Import this library into a programSDFileSystem

SDFileSystem

Last commit 29 Nov 2012 by user mbed official

Details

SD Cards are widely used by loads of devices for storage; phones, mp3 players, pc's etc. That means they are a very cheap option for storing large amounts of non-volatile data (i.e. the data is not lost when the power is removed). They should be ideal for data logging and storing audio/images.

SD and MMC cards support various protocols, but common to them all is one based on SPI. This is the one used here as, whilst not being the most high performance, it uses a generic SPI interface so will be more portable.

SD Cards are block devices. That means you read/write data in multiples of the block size (usually 512-bytes); the interface is basically "read from block address n", "write to block address m". Note that a filesystem (e.g. FAT) is an abstraction on top of this, and the disk itself knows nothing about the filesystem.

Based on a SparkFun MicroSD Breakout Board, here is the wiring that will work (you can obviously use either SPI port, and any DigitalOut):

/media/uploads/simon/usd-breakout_i_ma.jpg

SparkFun MicroSD Breakout Board
MicroSD Breakout    mbed
   CS  o-------------o 8    (DigitalOut cs)
   DI  o-------------o 5    (SPI mosi)
   VCC o-------------o VOUT
   SCK o-------------o 7    (SPI sclk)
   GND o-------------o GND  
   DO  o-------------o 6    (SPI miso)
   CD  o

Warning

Note that VCC is 3.3V from mbed's VOUT pin. Do not use 5V from mbed's VU pin. 5V power may damage the SD card.


The CD (card detect) pin is optional and not used in the example program, but it can be used to detect a card in the micro SD socket. CD connects to ground when no card is present. No connection is made once a card is inserted. It can be read using a DigitalIn pin, if the mode is set to PullUp.

Reference



Post a comment Ask a question
Last modified 15 Feb 2013, by user Samuel Mokrani. 38 comments tag SDCards, SDFileSystem, SPI

2 related questions:

1
answers
mbed_debug.h ??? user Tyler Weaver
5 months, 1 week ago

tag card, file, SD, System

0
answers
How do I get the SD lib to work with the sparkfun CAN-bus shield? user Eric Fossum
18 hours, 7 minutes ago

tag KL-25Z, KL25z, SD, SD Card, SD Card File System


38 comments:

user John Knott
23 Jul 2010

I am using a cool components mbed workshop breakout board modified your latest SDcardtest as shown for cool components mbed workshop breakout board

SDFileSystem sd(p11, p12, p13, p27, "sd"); SDFileSystem sd(p5, p6, p7, p8, "sd"); my cool components mbed workshop breakout board

Target is Fuji 2Gb from RS components 375-953 less than £10 inc vat with SD adapter works straight out of the box well done. I just checked that it was Fat 16 when delivered, it was.

user John Knott
23 Jul 2010

Sorry my cut and paste does not seem to show SDFileSystem sd(p11, p12, p13, p27, "sd"); was commented out with and replaced with SDFileSystem sd(p5, p6, p7, p8, "sd"); my cool components mbed workshop breakout board

user John Knott
23 Jul 2010

sorry sorry something is incapable of showing double slash but hope you got the message

user Edward Carter
29 Aug 2010

Worked for me using the Cool Components Breakout board and a 2GB PNY card. I continued to get the error message "No disk, or could not put SD card in to SPI idle state." UNTIL I made your change above ... works flawlessly!

user Hugo Vincent
02 Nov 2010

Is there a way to sync file writes to the disk without closing and re-opening the file? Standard methods (fflush(), fsync(), sync() etc) are either missing or don't seem to work...

user Sares Sares
13 Nov 2010

is it possible to see the content from the PC when the USB is connected, like the flash of the CPU of Mbed?

user Hugo Vincent
13 Nov 2010

@Sares, no, not currently. It would be possible with quite a lot of extra work (a firmware image for the mbed with additional support in the mbed interface chip firmware too) but I doubt the mbed team are interested in adding this support.

user Dan Minear
02 Dec 2010

I had to use this newer library to get my SanDisk 2GB micro SD card to work. I think this is the Jun 2010 version as opposed to the Dec 2009 library. I was able to write the demo file to the card.

user Daniel Near
04 Dec 2010

I also tried on a Sandisk 512mb microsd card and was successful.

user Didier Solheid
27 Feb 2011

Hi all,

I try to have my microSD board working with a 2Go card.. Without success :/

Any idea why the 4 leds on the mBed board are blinking ? Is to communicate a error state ?

Regards

[EDITED] =>

Ok, it's works with #include "SDHCFileSystem.h"

user Igor Skochinsky
27 Feb 2011

Didier, it's better to post about problems on the forums. That said, the blinking LEDs sounds like Blue Lights of Death

user Fidias Dimitriou
02 Mar 2011

Hello there anyone knows how i am going to read the free space of my SD card??

user Sunny Singh
18 Apr 2011

/media/uploads/RandomSingh/sd_card_corrupt_files.jpg

Hi All,

I am experiencing a weird phenomenon. I am running the SD card Hello world tutorial by Simon Ford. Using a freshly formatted 256MB SD Card the program runs smoothly with no errors. If I reset the mBed (using the reset switch) the program will run smooth again. If I repeat this process another 10 times (ish), the program then stops working and exhibits the blue lights of death. The serial out the messages back 'No disk, or could not put SD card in to SPI idle state'. This message continues to appear until the card is reformatted. Before formating I have noticed that there are some weird files saved to the SD card. I don't know where theses are coming from. I can only assume it is something to do with my hardware, perhaps interference. I am using a bread board. I intended to transfer on to strip board. I am posting this just in case someone else has seen this and can advise how I can fix this issue. Thanks.

user Sunny Singh
18 Apr 2011

**UPDATE** Have fixed the issue!!! It was interference!!!! Simply removed the huge header socket arrangement I had and now it works flawlessly!!!! :-) WKKWKF!!!

user elektronika7 elektronika7
27 May 2011

I connected mbed and SD Card Slot followed tutorial on this page,and SD Card is 64MB.I have problem with program SDFileSystem_Hello world. In Hyper terminal writing "Didn't get a response from the disk" and 4 led on mbed are blinking. Please someone to help me how can I fix this problem?

user Chuck Fricker
12 Jul 2011

Is there a way to get the SD Card status? disk_status() does not seem to return status of whether the SD card is installed or write protected.

user HM Yoong
12 Aug 2011

From the SDFileSystem.cpp file, I do not know how standard C buffered I/O functions such as fprintf(), fread(), fwrite() call the member functions in SDFileSystem. My questions:

a) How big is the buffer can be allocated by user? Any guide? b) Can I use unbuffered I/O function such as read, write, seek?

I am thinking to use the library to stored large files in SD card for data logging purposes. As data logging only insert at the end, so we may be able to improve performance without the buffering abstraction.

Any idea? Thank

user HM Yoong
12 Aug 2011

user HM Yoong wrote:

From the SDFileSystem.cpp file, I do not know how standard C buffered I/O functions such as fprintf(), fread(), fwrite() call the member functions in SDFileSystem. My questions:

a) How big is the buffer can be allocated by user? Any guide? b) Can I use unbuffered I/O function such as read, write, seek?

I am thinking to use the library to stored large files in SD card for data logging purposes. As data logging only insert at the end, so we may be able to improve performance without the buffering abstraction.

Any idea? Thank

I found the answers and get a solution from http://mbed.org/users/emh203/notebook/long-file-name-example-code/

user Andre Glaize
07 Nov 2011

Hi, writing and reading on a SD card is fine but could someone explain why there is no date for the file creation?

It is a bit analogous to writing on the flash memory where the creation date is always the same 01/01/20008 !

Besides I have the RTC running fine (to log messages) so the problem does not seem to come from the RTC, but from the SDFileSystem library may be? Could someone has a clue?

user ceri clatworthy
07 Nov 2011

I think Date/Time stamp is not implimented,

Sorry

Ceri.

user Roman Kuzmin
10 Nov 2011

How to check existing flash in the sd reader ?

user Zera Jera
26 Mar 2012

Hi,

Does anyone know the command to find the available space on an SD Card? That's not the capacity but the remaining space.

Cheers,

Zera

user Goran Jurkovic
23 Apr 2012

Is there a workaround for microSD cards larger than 2GB?

user mat besson
02 May 2012

user Goran Jurkovic wrote:

Is there a workaround for microSD cards larger than 2GB?

dowload SDHCFileSystem library

http://mbed.org/users/xxll/programs/SDHCFileSystem/5zdtq

I now work with a 8Go sd card

user james kain
14 Nov 2012

Example Program did not compile

I just tried the example Hello World SD File System Program. I added the exact code in the example to a new Project. Them I clicked "Import" on the action menu across the top. This let me select fraom a list of libraries. I see the "SDFileSystem" at the bottom of the list ... I click this and then click "import" at the top of this page. I see the the SDFileSystem folder been added.

When I attemp to compile this I get errors. The first error is Identifier "Namespace" is not efined in the resource FileHandle.h (error number 20)

Any ideas?

user Erik Olieman
14 Nov 2012

Apparently the program is missing fatfilesystem (http://mbed.org/users/AdamGreen/code/FatFileSystem/), add that to the project and it compiles.

user james kain
18 Nov 2012

Thanks Erik .. all works now. However, I am having a speed issue.

I am trying to read about 1000 bytes per sec from a GPS receiver in 4 binary messages. I write these out to the SD card one message at a time. I use the mbed rtos to create a separate thread for the write. Without the write I am able to capture the data just fine with no missed bytes.

However, the write to the SD card cannt keep up. I am using the SD breakout board and card from Sparkfun.

Is there a faster way to write to permanent media? How about the USB-to-flash library? Is the SPI clock speed fixed for the SDFileSystem? Does my throughput performance seem to make sense?

J

user Erik Olieman
18 Nov 2012

Sorry no experience with SD card library personally. However RTOS has 1ms ticker, that might be way too long for your requirements.

user Kevin Hobbs
18 Nov 2012

Hi james, I'm sorry I don't have any expertise in this area but thought this post might be something for you to watch and study?

https://mbed.org/forum/mbed/topic/4140/

user Keith McLaurin
20 Nov 2012

user james kain wrote:

Thanks Erik .. all works now. However, I am having a speed issue.

I am trying to read about 1000 bytes per sec from a GPS receiver in 4 binary messages. I write these out to the SD card one message at a time. I use the mbed rtos to create a separate thread for the write. Without the write I am able to capture the data just fine with no missed bytes.

However, the write to the SD card cannt keep up. I am using the SD breakout board and card from Sparkfun.

Is there a faster way to write to permanent media? How about the USB-to-flash library? Is the SPI clock speed fixed for the SDFileSystem? Does my throughput performance seem to make sense?

J

The SD cards have their own controller in them and speeds depend on the chip and technology used. I find the SDHC cards are much faster than SD. An additional boost can be expected from cards with high data rates e.g. class 10 is faster than class 4.

Hope that helps. You may have to implement a larger ring buffer to hold the data while the SD card is busy.

Regards

hi, We are going to use a SD card to write and store data while the main program is running. When we implement it with MBED RTOS, the threads stop working. A file is created and the test print was also there.

How to use SD card along with threads??

user Richard Darling
05 Dec 2012

user james kain wrote:

Example Program did not compile

I just tried the example Hello World SD File System Program. I added the exact code in the example to a new Project. Them I clicked "Import" on the action menu across the top. This let me select fraom a list of libraries. I see the "SDFileSystem" at the bottom of the list ... I click this and then click "import" at the top of this page. I see the the SDFileSystem folder been added.

When I attemp to compile this I get errors. The first error is Identifier "Namespace" is not efined in the resource FileHandle.h (error number 20)

Any ideas?

user Erik Olieman wrote:

Apparently the program is missing fatfilesystem (http://mbed.org/users/AdamGreen/code/FatFileSystem/), add that to the project and it compiles.

I've got the same problem. I've added the library FatFileSystem to my project folder, but still get errors at compile time, starting with -

Identifier "namespace" is undefined

I must be missing something simple, but I don't know what it is! Can anybody help? I'm new to this. Thanks very much.

user Emilio Monti
07 Dec 2012

We added an officially maintained SD File System library:

» Import this library into a programSDFileSystem

SDFileSystem

Last commit 29 Nov 2012 by user mbed official

Let us know if you experience any problem with it.

Cheers, Emilio

user Yoshi Mimura
25 Jan 2013

user Emilio Monti wrote:

We added an officially maintained SD File System library:

I just tried the new library.
Nice to know that it now supports time stamp and long filename.

Thank you!

user Hao Yan
01 Feb 2013

I'm having trouble to get it to work. I use a 1G MicroSD card, but the program always stuck at mkdir("/sd/mydir", 0777); After I pull the card out, the program seems to be able to proceed... and it didn't report error.

user Hao Yan
04 Feb 2013

user Hao Yan wrote:

I'm having trouble to get it to work. I use a 1G MicroSD card, but the program always stuck at mkdir("/sd/mydir", 0777); After I pull the card out, the program seems to be able to proceed... and it didn't report error.

I got it to work. The problem was I connected VCC to VIN rahter than VOUT.

user Yoshi Mimura
14 Feb 2013

user Yoshi Mimura wrote:

user Emilio Monti wrote:

We added an officially maintained SD File System library:

I just tried the new library.
Nice to know that it now supports time stamp and long filename.

I tested the new library further.
Found it now supports FAT32, SDHC cards (more than 4GB media) and a single file can be more than 2GB.

I believe everyone would like to see these new features on the top of this page.

user Jheewon Chun
10 Mar 2013

Is there an example of how CD would work using DigitalIn and Pullup?