Using SD cards with large block lengths with LPC2148

Development Boards MicroMod
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Hi. I am not sure if this is the correct place to post this, but it kinda relates to the LPC2148.

Sorry if this is common knowledge or something, but I can’t seem to find good information on this anywhere. I am attempting to use a [LPC2148 demo code, specifically, I am trying to use the [FatFS code to get the controller to talk to a memory card. It does work for some cards, but not for others. I believe the reason stems from some cards having a non-standard block size. I have one card (2GB not SDHC) which reports a block size of 1024. The read function fails when attempting to read anything from this card, and near as I can tell, the card stops responding after the first read (I get one 512 byte chunk of good data and then nothing but 1s).

Reading the [SD Card Specs I came across two interesting tidbits on page 96:

In case of Standard Capacity Card, the size in the data token is determined by the block length set by SET_BLOCKLEN (CMD16).

The maximum block length is given by 512 Bytes regardless of READ_BL_LEN, defined in the CSD.

I use CMD16 to set the block length to the maximum value in the CSD (1024) during the card initialization routine. From what I understand, that should make the read command return that number of bytes. However, it seems like from the second quote, that I am not allowed to do this. Has anyone else run into this problem? and if so, what is the proper solution.

I will probably try to set a smaller block size with CMD16 and see what happens, but I am running out of ideas.](http://www.sdcard.org/developers/tech/sdcard/pls/)](FatFs - Generic FAT Filesystem Module)](LPC2148 Demo Code Overview)

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No SD card experts here, I guess. :frowning:

For future reference: I tried setting the block length to 512 using CMD16, and telling the program to ignore the larger block size, and it seems to be working. I have not had too much time to test it, but I can read files off the card (or at least, the names of the files).

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FAT assumes 512-byte sectors. Set the block length to 512. If the card can’t handle that I’d toss it in the bin.

Edit: I should have said most FAT implementations.

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Right. The problem came from the initialization code setting the block size to the maximum allowable, which for some cards is more than 512 (it was 1024 in my case). I added a check that limited the block size to 512 and all seems to be well. I can write ~3000 conversions from the A/D to the card per second. :slight_smile:

Now to try and get the Ethernet working…