FAT16 file system for MMC using SPI interface

Douglas Kennedy · Joined: 07 Sep 2003 Posts: 755 Location: Florida

This code was written as a hobby project at a time when MicroSoft specifications were public and its patents were undecided by US Courts. I sent this code to some one in England who then against my wishes placed the code on the web. In response I considered
(especially since the Microsoft patent wasn't yet decided in fact it had been denied) it would be better to post the code on this board since it could be accompanied by appropriate disclaimers. After a change of Administrations in the US the patent office reversed itself and upheld Microsoft's patent.
Writing files brings a person much closer to patent infringement than reading
so the code gives no encouragement or examples whatsoever about writing files. I have never written files using this code to any Microsoft operating system even though I own my computer and it's in my own home. Again FAT is fully owned by Microsoft and everyone should seek legal advice so as to respect fully Microsoft's ownership rights. Permission to use FAT can be obtained from MicroSoft for around $250,000. Anyone using FAT would be well advised to obtain Microsoft's permission. Microsoft is trademarked and is used here only to provide context.

miky · Joined: 06 May 2007 Posts: 10 Location: Prague

Hi Douglas,
trying to run the code on 18f452 (20Mhz) on Kingstone 512MB SD card. I've changed the init:
c=mmc_cmd(0x77,0x00000000,128,0x00,0x99);
c=mmc_cmd(0x69,0x00000000,128,0x00,0x99);
if (c==0x00) { goto ready;}
so the init SD works. I've placed 120MB file on the card and I can read the card via file_read properly. I am also able to write into file (with SPI_CLK_DIV_64 when using resistors as 3.3.v dividers) but with following issues:
1. when the resulting file is <5kB then it works, SD is readable on PC reader
2. when the resulting file is ~128kB then I see in debug that clusters are modified and FAT is updated - each FAT update takes aprox 10s!
3. when reading from pic I see some corrupt data around cluster updates
4. when reading SD from PC reader the file is corrupt and unreadable.
The write loop is as follows (buff0 is 128):
int32 ofst = 128;
...
error0 = file_set(0,ofst);
error0=file_write(0,buff0);
if (error0>0 && error0<255 ) {
printf("\n\r fwrite 0 failed error=%U\n\r",error0);
goto mmc_exit;
};
ofst = ofst + 128;
....
Any hint how the proper write sequence shall look like (e.g. are the clusters changes fully handled in file_write routine?.
Thanks,
Miky

sauer · Joined: 02 Jul 2007 Posts: 2

Annyone have the actualized driver mmcdos.c? I tried the code listed by Douglas Kennedy an it doesn't work. I can't compile it. I'm using the CCS 4.020 version. I try to compile using the PIC18F252.

etiedon · Joined: 23 Jul 2007 Posts: 12

I have a problem like that;

Library works perfect with mmc3.0 (16mb)

And when using read_BLOCK response of r1 is 0

But when i use it with reduced-size mcc (512 mb) when i use read_BLOCK response of r1 is 255..So it doesnt read properly.

What is the meaning of r1 response(255) ? And what is the possible solutions?

Thanks for your help.

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

etiedon · Joined: 23 Jul 2007 Posts: 12

Pret · Joined: 18 Jul 2006 Posts: 92 Location: Iasi, Romania

app · Joined: 09 Feb 2008 Posts: 1

hi

function set_BLOCKLEN is not work.
r1=mmc_cmd(0x50,size,16,0x00,0x40);

Response r1 is not 0x00

ratgod · Joined: 27 Jan 2006 Posts: 69 Location: Manchester, England

Does anyone have any example code of reading text from a test file?
I have the card initialized ok, it appears to find the file ok but when I do a read I don't get anything back.

any ideas or examples?

also, does anyone know how to specify the filename correctly? I'm using "test" as a file name as I'm not sure how to get it to work with "test.txt"

thanks

emresensoy · Joined: 27 Dec 2008 Posts: 2

Hi to everyone,
I use this code with 18f452 with 1gb sd, 128 mb sd and 64 mb sd card,
and everything is ok.
But with 1gb sd card if a file data is at address like 29589000
the open_file routine works, there is no problem, but the file_read
routine doesn't work.

manish12 · Joined: 18 Jan 2009 Posts: 15

harrie215 · Joined: 15 Apr 2005 Posts: 6 Location: Netherlands

husam · Joined: 17 Feb 2010 Posts: 10 Location: jordan

hi ,
is necessary to use PIC18F452 only ?? if no how .. ??

noyz · Joined: 31 Jan 2009 Posts: 59

I am wondering. Is it possible to use MicroSD as both as FAT file system
and as an external memory.
ex:
Write to file different types of string...
and have a memory very accessible like RAM.. write at 0x20. Something like that.

I want to have a vector really big and it doesn't fit in MCU ram.
Should I use a file or is it possible what i wrote up.