SD memory card what is the dirty little secret.

[Hans Wedemeyer]

This is a long post, but without the details it may be even more confusing...

I've been using the SD card for a while. My original attempt at reading a card with some code given to me, left me with a working system that could only read a particular 32Meg card, I was convinced I did something wrong and could not find the problem.

I needed to move on and purchased an Atmel SD card library, and ported it to the PIC18 with good results. I was then able to read a lot more SD cards.

Recently I've run into a problem with certain brand name 32 meg card (Delkin, & HP) that I cannot read, and today I got (eBay) a bunch of 16 meg cards that I also cannot read.

These 16 meg cards come formatted with FAT12, and I need FAT16. So I formatted one and it works OK on the PC using a USB SD card reader.

My PIC project cannot read these cards.

So I did something I had considered doing for a while and wrote my own version of a format function for the SD card, on my PIC project hardware.

The results is I can now read and write to the entire card.

Here comes the reason for my post:

The card I inserted was according to the USB reader and WinHex FAT12 .

My hardware formatted it to FAT16, and it is 100% OK to read and write. Using the ICD-U40 debugger the boot sector entries are correct for a 16 meg card. So My code did the trick.

I then plugged that card back into the USB read and looked at my handy work with WinHex, and found the bot sector was still reporting it as FAT12 with correct entries for FAT12...

I inserted it into an iPAQ and used a flash format program, which reported it as FAT12.... ! Put it back in my PIC hardware and it works as FAT16 and the debugger confirms the boot sector reads as FAT16 !

I got 10 cards and have reproduced this effect TWO time... I'm saving the other 8 card for show a few people in the coming days... These are people that would normally call me nuts and so I have to defend the little bit of sanity I still have :-)

So what is the dirty little secret behind this SD card boot sectors. I have confirmed the USB read is NOT using SPI to read/write the card, I am using SPI.
I have no concrete evidence to prove this:
However it looks like the SD card interface has access to a different copies of the FAT. One for the 4 wire hardware and one for SPI interface...
It is the only logical reason I can come up with (pure guess work) as to why the two FATS coexist on the same card and appear to both start at address 0.

This SD card "thing" is not a clear cut as many have indicated....

I wonder why the SD card org. wants $11,000.00 for membership, is there a dirty little secret about the SD card that they hope $11K will prevent the rabble from finding out.... ?

As we all know the MMC morphed into the SD card , the SD card connectors prove the SD card was an after thought. i.e. poor planning when the MMC was born.

[Steve H.]

Ouch! You have convinced me to stick with CF cards or my own Flash EEPROM dongles!

That is really weird...

Steve H.

[lucky]

Wow, that sounds real nasty.

I use CF in my MP3 player project but almost went the MMC/SD route.
_________________
Lucky
www.mpic3.com - MPIC3 player project, Forum, Downloads, Online Shop

[ckielstra]

Hans,

There are several documents describing the SD-card:
* "SD Memory Card Specifications, part1 physical layer specification"
* "SD Memory Card Specifications, part2 file system specification"
* "SD Memory Card Specifications, Secure Digital Input/Output (SDIO)
Card Specification"

A simplified version of the first and third documents can be found at the Sandisk website http://www.sandisk.com/industrial/manuals.asp and also via links at http://www.sdcard.org/sd_memorycard/index.html.

The second document is way more interesting for your problem and I haven't been able to find this on the internet. The full documents are confidential and I guess the reason for this secrecy is that they want you to pay a substantial amount of money for use of their patents.

Where did you find the information of a $11,000 membership? The information I found starts at an annual $1,500 Membership fee and annual $1,000 license fee (per product?).

[ckielstra]

I don't know, but could your problems with some of the cards have something to do with multiple partitions on your flash card?
Because you wrote your own formatting routines you are quiet sure to have created a new Master Boot Record (MBR), but are the USB devices (under Windows?) looking at the MBR or are they looking at an Partition Boot Sector (PBS)?

In the Sandisk SD Card Product manual I found the following which made me wonder:

[Guest]

[Guest]

[Hans Wedemeyer]

Not sure what to make of this yet:
Formatted a 16MB card to FAT16 on the iPAQ and confirmed it "took" by using WinHex on the PC with the UBS reader.
Put the card in my hardware and read 00 at all boot sector locations.
Formatted the boot sector in my hardware to FAT16. Read that same boot sector and it reads correctly.

Using WinHex wrote 00 to every location.
After that I tried to open the card(drive) again using WinHex and WinHex complained it could not read the card....

So that confirms the boot sector has 00 in all locations.

Put the card back in my hardware and it read the FAT16 boot sector correctly !
Wrote the boot sector and FAT again.

The card shows up as a 7 meg card, of half or partition is used. !

With my hardware/software made two directories.
folder1
folder2

Read the card again using WinHex and WinHex was able to read the FAT as FAT16, and WinHex found the two folders. However Explorer reported one folder but name was wrong !

In the iPAQ flash format reported 2 sectors per cluster ! Yet the FAT16 my hardware/software wrote was 1 sector per cluster.

Formatted on the iPAQ using Flash Format to 1 sector per cluster and enabled the Backup FAT.

Put the card back in my hardware and am able to write to the two ORIGINAL folder1 and folder2 !

I think this confirms the iPAQ using Flash Format uses a copy of the boot sector and FAT.

Put the card in the USB reader and made two directories
ABC345
ZXY123

Confirmed Windows File explorer was able to "see" these, and also the iPAQ.

However my hardware only sees the folders it made and still only reports 7 meg...

Initial conclusion there are two partitions that are only seen by the respective hardware that made them.

Winhex can see the folder entries for folder1 and folder2 and they are at 0X15800 which is not the root directory as reported by WinHex , also WinHex reports only one FAT !
Yet I enabled the second FAT in the iPAQ.

So if you want to lose data fast... Write your own FTA in PIC hardware and if you then write something on the PC with a USB ready .... chances are you will blow away your PIC/FAT..... !

Clearly there are two boot sectors and different FAT's .
Getting these to be synchronous seems to be the task at hand.

Perhaps the CSD register holds the clue...

I think this is the biggest mess I have ever seen.... I do think the SD card org. are sitting on a dirty little secret.... and the $11K membership fee is a crude ( and futile) attempt at keeping the secret under lock and key.

I hope I can nail down what is going one and then expose it all to the world...

Shame on the SD Org. for not making this public....

After all we are the customers trying to use this product, why does they think putting hurdles in our way will endear us to this SD card....

I'm also upset at the arrogance of Sandisk... perhaps I should buy some shares and then show up at one of the share holders meetings and voice my opinions to the board of dircetors and other share holders... I expect it will fall on deaf ears...

The only thing stopping me going CF is that horrible socket, it looks like a nightmare to solder.

[Douglas Kennedy]

The identification of a FAT16 formatted card or FAT12 is a softee issue. I believe the format FAT12 or FAT16 is assumed by the softees based on the (count of clusters) logical capacity of the card not on the actual software format. If the cluster count is less than 4085 its FAT12,
4086 to 65525 FAT 16 So a small capacity card formated at FAT 16 ( Ex 16 mb) may be asssumed to require FAT12 format if the softee system sees it in a format drive scenario. A drive could be formatted as FAT16 but if the total clusters is less than 4085 the softees will assume FAT12.

[Guest]

[ckielstra]

[Hans Wedemeyer]

[ckielstra]

[Nick]

if your looking for old files check the web archiver. The way back machine archives can help you get old files, I use that website so much, its almost abuse.

Nick

[Jerry I]

Reading about your problem I had found some app. notes on web.

Don't know if they will help.

Links

http://www.intel.com/design/pca/applicationsprocessors/applnots/278533-001.htm

http://www.tomsnetworking.com/Sections-article82.php

Good Luck