Micro SD card / MSP430 interface: write problem

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My experience with SD cards and the MSP430 has led me to believe that almost all errors are related to the timing of operations. In=20 particular, the time for the SD card to indicate that it is ready for a new write increases drastically when the card's internal processor decides it is time to erase a new block of the flash so that new data can be written. On one set of cards, this happened at 32KB intervals. At that point, the time to write a block=20 (after waiting for the card to indicate it is not busy) would bump up from a few milliseconds to over 50 mSec. The delay probably depends on the speed rating of the card.

My technique for debugging these issues was to toggle an I/O bit at the start and end of the write function and observe the=20 timing.

Of course, the other possibility is that your write routine isn't sending what you think it is. Perhaps you could repeat your test, but insert code in the routine that writes the buffer to check to make sure it isn't writing a buffer full of zeros. A wayward buffer pointer might cause something like this.

Mark Borgerson

Mark Borgerson a écrit :

Thanks Mark for your answer,

I did print my buffer before sending it, it is correctly filled, but when I do outputs on the serial interface, write errors do not occur. Generally speaking, they do no occur if I add delays (by adding printf, or anything that is a bit time consuming). It seems to corroborate what you say. If I understand well, you say that even if the card is telling me it is not busy it might actually be? Is there any mean to know that? (other than waiting for XXX ms) I've seen that it is possible to pre-erase block, would it help? For the record, I do write operation about 1 to 5 times per second (512 bytes blocks).

Christophe

Mark Borgerson a écrit :

Hi,

I have read once again the SD simplified specification and Samsung MicroSD Card datasheet, it seems that there is a flag called READY_FOR_DATA in the card status (not in SD Status register) that indicates the card accepts write operations. It seems to be accessible in the R1 response but only in SD Mode, I have not seen any mean to access this bit in SPI mode, does anyone know how to have this information?

Christophe

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Have you tried your code on a SanDisk micro SD card? I have found that different manufacturers have very different delays before the card is=20 ready.

In my SD_Send_Command code, I execute the following check whenever the=20 LAST operation was a write i =3D 0; SD_CS_ON; // macro to set CS bit low do { // Check for card busy =09if(i++ > 30000) break; uc =3D Get_SD_SPI(); // get a byte from the SPI } while(uc =3D=3D 0); // uc stays zero while card busy ..... // more code to actually send the command

At the processor and SPI clock speed I am using, 30,000 times through this loop is about 100 milliseconds.

At one time, I added code to keep track of the loop count in=20 this routine. IIRC, it was normally under 20, but would bump up to the 30,000 limit at times.

I also have code that checks for valid responses to commands. If I don't get a valid response, I increment a soft error count and try the command again---including the wait for the card to be not busy. I generally see two or three of these soft errors in an hour----indicating that the write command timed out. If I get 5 consecutive soft errors, I increment a hard error count, power down the card, reinitialize and start over with the command. This can take almost a second. Thankfully, I have not had any hard errors in the last few months.

Mark Borgerson

Mark Borgerson a écrit :

I added exactly the same kind of code after reading the samsung datasheet on micro SD (the description of SPI protocol is far more detailed than in the simplified SD specification). I have not seen any write problem ever since. But has Dijkstra said, test can only show the presence of bug not their absence ;)

Thank you again for your advice I'll keep in mind your system for error recovery, this might be useful

Christophe

Is this data sheet online somewhere ?

Google has not turned it up for me. :-(

Thanks

don

I found it here:

Christophe

Hello Christophe,

I read your posts and found that you have done something exactly I am doing these days. I have developed FAT32 file system on micro SD card using Freescale's MPC5554. I am using 4GB class 4 Kingston card. My read/write in file is working absolutely fine. The problem I am getting is with speed. When I use 3MHz SPI clock, I can write 1MB of data in 1 min which is pretty low speed!! When I try to use SPI clock above 3 MHz (after initialization), I am not able to read / write from the card. What is your speed of data transfer with SD card? I have read that I can go up to 25MB/s of speed by using 4 data lines. What maximum speed I can go up to using SPI mode (that is single data line)and how can I achieve this speed?

I would be so grateful if you could please help me. I have been working on this problem a long time but couldn't find any solution till today.

Thanks, Sana

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