RE: Creating file on SD card results in SFN even with LFN enabled

wgeeurickx — Thu, 09 Apr 2026 08:41:37 GMT

Hi Kenneth,

Thank you for getting back to me, and sorry for my delayed response. I have been busy with some other work the past weeks.

I know that I need to enable CONFIG_FS_FATFS_LFN, this was also indicate in my original post. I have narrowed down the main issue to something weird happening with how the module is operating depending on how it is included in the build.

When I keep the drv_sdhc.c file inside /src and include it in the build in my CMakeLists.txt in /app, it seems to work as expected. However, when I move it to a directory in /drivers (and make sure that everything is set up so that the file is included in the build), I get the issue described above.

Another issue I observed is that I store a pointer to an application callback function inside the drv_sdhc module, essentially to let the application know when the SD card is inserted. When I initialize the driver and set the pointer, everything is fine. But when I actually get the GPIO callback indicating that the SD card is inserted, I notice that the pointer variable has changed and is no longer pointing to my actual callback function, but rather 0xaa550000, which is not a valid address

These things seem to be connected, as this also doesn't happen when I'm doing it from the drv_sdhc.c file in /src . I have made other /drivers, so I'm pretty sure it's not related to how it's implemented. But I'm lost as to finding out what exactly is going wrong. The good thing is that I can make things work by just doing everything in /src, but I would definitely want to understand the issue.

RE: Creating file on SD card results in SFN even with LFN enabled

Kenneth — Mon, 23 Mar 2026 12:56:42 GMT

Hi,

Searching in nRF Connect SDK I can find for instance in test_fat.h that:

#if defined(CONFIG_FS_FATFS_LFN)
#define TEST_FILE	FATFS_MNTP \
	"/testlongfilenamethatsmuchlongerthan8.3chars.text"
#else
#define TEST_FILE	FATFS_MNTP"/testfile.txt"
#endif /* CONFIG_FS_FATFS_LFN */

I can also find in kconfig.fatfs

config FS_FATFS_LFN
	bool "Long filenames (LFN)"
	help
	  Without long filenames enabled, file names are limited to 8.3 format.
	  This option increases working buffer size.

So it looks to me that you need to enable CONFIG_FS_FATFS_LFN=y to support longer than 8.3 file name yes.

Kenneth