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SDcard Read/Write missing/wrong data

Wouter Schol

Hi there,

I am using an own PCB with Luminary lm3s8962 (based on the evaluation board) with LabVIEW for ARM and KEIL uVision V3.85

In the past I've been developing code to, Log some data to/Read logfiles from, a microSD card without problems.

The data that is being logged is become a little bit more and at this moment I get corrupted data on/from the microSD card. I am using SanDisk 2 GB microSD's.

problem one: When I write enough data for a longer time I see that sometimes the data is wrong. I tested this behavior and I can reproduce it. The data size is OK but where I expect data like:
112;112;112;112;112;112 I see:
112;112;11;111;1112;112

sometimes the SDcard copies old or wrong data to that position that is wrong.

I've made a change which decrease the buffer per write. Now I don't see this problem anymore.
Is this an known issue?

problem two: When I read files from the microSD card on my embedded ARM and read the data via USB, I get wrong data (the first bytes are looking like a directory table of FAT)
I didn't made any change to the USB Read protocol and I wipe the microSD before every test.

When I read the microSD card in Windows, there are no problems.
Is there someone that is also getting strange behavior like this?

Parents
  • 0 in reply to Wouter Schol

    Have you checked if the cards are created with same-size clusters or same-size sectors?

    Since a FAT-16 file system can only map 2^16 different memory blocks, the data is stored in clusters of one or more sectors.

    The cluster size controls how long the FAT chain needs to be for a given file size. And cluster size also controls how large partition that may be mapped by the 16-bit cluster numbers you have in FAT-16.

    A 4GB card with 2^16 clusters needs 65536 byte large clusters.
    A 2GB card only needs 32768 byte large clusters.

    The 2GB card will then have twice as long FAT chains for a file of same size.

Reply
  • 0 in reply to Wouter Schol

    Have you checked if the cards are created with same-size clusters or same-size sectors?

    Since a FAT-16 file system can only map 2^16 different memory blocks, the data is stored in clusters of one or more sectors.

    The cluster size controls how long the FAT chain needs to be for a given file size. And cluster size also controls how large partition that may be mapped by the 16-bit cluster numbers you have in FAT-16.

    A 4GB card with 2^16 clusters needs 65536 byte large clusters.
    A 2GB card only needs 32768 byte large clusters.

    The 2GB card will then have twice as long FAT chains for a file of same size.

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