FAT_FS f_write: Writes wrong data to file when writing odd number of bytes

GS1 · ‎2019-08-19

Hi all,

In my project with STM32H743 (created with CubeMX version 5.0.1) I have a strange behaviour of f_write when writing data to the file and the amount is not a number which can be devided by 32.

In my test I wrote 256, 512 or 4096 Bytes at a time. Everything perfect. Data in File as expected.

BUT: When writing e.g. 590 Bytes (which is not dividable by 32) -> Errors appear.

I create a test file with following text pattern (590 Bytes)

0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklm

0123456789##

This pattern is written to a file 100 times appending to an open file.

Now the result shows wrong blocks after multiple writes. Here is the wrong part:

0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklm

0123456789##

012345678989:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklm

0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklm

01234567:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklm

0123456789##

0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklm

In one block 2 characters are moved around to the wrong place!!

It seams that this issue only appears when writing a number of Bytes which is not dividable by 32 at a time, 256 is ok, 512 is ok, 4096 is ok, but: 590 is not ok! (This is just an assumption on the current state of testing)

Can anyone help?

ff.c Revision:

#if _FATFS != 68300 /* Revision ID */

Tesla DeLorean · ‎2019-08-20

CRC32:03F105CE Memory

20000DF8 20000E00 16384 TEST.TXT

.

CRC32 03F105CE PKZIP FC0EFA31 TEST.TXT

CRC32:03F105CE File

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GS1 · ‎2019-08-21

Hm... ok, looks fine.

Thank you! Let me see, what I can find out...

RSouz.1 · ‎2021-01-19

Hi everyone.

I had the same issue. I updated the version of FatFs library to the version R0.14a and the issue keeped happening. The unique workaround that worked for me is this solution to only request to write an amount of bytes dividable by 32.

Piranha · ‎2021-01-20

That's an indication that the cache management is flawed.