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AT89C51ED2 FAt16

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jameslys

Sun Sep 07 2008, 09:49PM

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If the fat16 is fragmented, how to get the next cluster value after i accessing the starting cluster? If the current cluster is the end of file, is it will show that the next cluster is FFF8 - FFFH? If the is multiple files in the fat16 farmatted sd card and a structure is declared for user selection later, how to add the root directory of each files into the structure by skipping the empty entries. And how to determine that current sector read is the last sector in the cluster? is it by comparing to the size of cluster?

Ajay

Mon Sep 08 2008, 02:19PM

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I want you to try it on your own.. to see how FAT16 FS looks like

Download HxD (hex editor) from http://mh-nexus.de/en/
and view files in you MMC/SD. see how MBR is constructed. Check sector 0.
See how FAT is allocated in MMC. How files are linked and lot more

It will be a good working experience on FAT.

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nismo

Tue Sep 09 2008, 12:30PM

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yoyo, what is your progress. i have just started FAT16 yesterday. Feeling lost.. haha. Hope everything is fine. Good luck pal

nismo

Tue Sep 09 2008, 12:55PM

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Err, i have tested the software that Ajay has uploaded. Actually our data is represented in ANSIC. I wonder what is the connection of this with FAT. I remember that the offset of the FAT16 is 2 bytes only. But the HxD is more than that. But i have a better picture of how the file is being encoded. Thanks man...

Ajay

Wed Sep 10 2008, 01:37PM

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Nismo,
FAT is a table that maintains the file structure of a disk. Theoretical knowledge always tells you things but you can understand those things better, if you can see them practically. So open the FAT16 specifications + your MMC drive in the software parallel.

To know things better, try doing this..
format your MMC drive in FAT16, create two small files abc.txt and efg.txt and see how they are stored in MMC sector vise.
think yourself as a controller and try to understand how would you read file from a given start sector

that will solve all your problems.

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nismo

Wed Sep 10 2008, 09:45PM

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Oh yea, how come i never think of this. Thanks man

nismo

Sat Sep 13 2008, 01:51AM

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Do you have anyway to access a sector of the SD card? Any example?

i mean access the sector. i have tried to write a code to access the sector in the sd card. the internal memory is not enough to accommodate my array as big as 512...

void readSector (unsigned long sector){
unsigned int count = 0;
unsigned char buf[SECTOR_SIZE];

sector += sectorZero;
sector *= 2;
setBlockLength ();
CMD (0xFF);
sendBlock ();
if(SPDAT == 0x00){
for(count = 0;count<SECTOR_SIZE;count++){
buf[count] = SPDAT;
}
}
if(buf[54]==0x46)
LCD_sendString ("F");

CMD(0xFF);
}

here is my code

[ Edited Sat Sep 13 2008, 11:18PM ]

luckynumber

Sun Sep 14 2008, 01:43AM

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this is MBR that i view from HxD

according to thr master boot record table

Offset Description Size
000h Executable Code (Boots Computer) 446 Bytes
1BEh 1st Partition Entry (See Next Table) 16 Bytes
1CEh 2nd Partition Entry 16 Bytes
1DEh 3rd Partition Entry 16 Bytes
1EEh 4th Partition Entry 16 Bytes
1FEh Executable Marker (55h AAh) 2 Bytes

the 1st partition entry should be at 1BEh, but from the HxD, the content of 1BEh is the ancii of 'o'

is my understanding correct?

[ Edited Sun Sep 14 2008, 02:14AM ]

nismo

Sun Sep 14 2008, 07:46AM

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But according to Mr Siew, that is not MBR but FAT Boot Record. If you use xp to format your sd card. There will be no MBR anymore. Anyway, it is told by Mr Siew...

[ Edited Sun Sep 14 2008, 07:49AM ]

nismo

Tue Sep 16 2008, 01:18PM

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How to retrieve a single element in one sector. i have got the data token sent by the sd card. But i can not get the data in it? What am i suppose to do? Below is my code

unsigned char readSector (void){
unsigned long i;
unsigned char buffer[SECTOR_SIZE];
L5:
sendBlock(); /*CMD17*/
clock(0xFF); /*8 clock cycle*/
clock(0xFF); /*8 clock cycle*/
if(response == 0x00){
L4:
clock(0xFF);
if(response == 0xFE){ /*0xFE is the data token*/
for(i=0;i<SECTOR_SIZE;i++){
buffer[i]=SPDAT; /*to store 512 byte data into buffer*/
}
clock(0xFF);
clock(0xFF);
}
else{
goto L4;/*if data token of 0xFE is not received go to L4*/
}
}
else{
goto L5;/*if the response 0x00 is not received go to L5*/
}
LCD_sendString("Processing"); /*If the card can get the data token 0xFE, the LCD will display 'Processint'*/
SD_cs = 1;
clock (0xFF);
return i;
}

void fileSystem (void){
unsigned char buffer[SECTOR_SIZE];
readSector(); /*Refer to the routine above*/
if(buffer[54] == 0x46) /*if the element in this array is 0x46, then it will print FAT16*/
LCD_sendString("FAT16");
}

i want to know whether array element 54 is 0x46 or not. If it is, the it is FAT 16... I find no problem with the code, but i still can not get what i want. Oh my, i already don't sleep for one day...

[ Edited Tue Sep 16 2008, 01:29PM ]