USB MSC very slow to enumerate SD card formatted with FAT32

[Gowri_M]

Hi,

We are using a custom board based on STM32U5G7VJTxQ and implementing USB Mass Storage Class (USBX) to expose an SD card formatted with a file system created using FileX.

The SD card when formatted with FAT32 (using FileX API), the USB mass storage device takes a very long time to become available on Windows.

Observed behavior:

• As soon as the USB cable is plugged in, Windows shows a pop-up message:
  "Please insert a disk into USB drive"
• After approximately 3-4 minutes, the drive finally appears automatically and becomes accessible.

Once the drive is mounted, it works normally.

We would like to understand:

• What could cause this very slow enumeration/access time with FAT32?
• Are there any known limitations or required configurations in USBX + FileX when using FAT32?
• Could this be related to SD card access speed, cluster size, cache configuration, or USB MSC parameters?
• Are we missing any required FileX, USBX, or HAL configurations specific to FAT32?

Any guidance or suggestions would be appreciated.

Thank you!

[Andrew Neil]

Is this on just one Windows Host, or have you tried more?

What Windows version(s)?

 

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@Gowri_M wrote:

Any guidance or suggestions would be appreciated.

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Have you tried instrumenting your code to see what's going on in your system ?

Have you tried any Windows USB diagnostic tools to see what's going on in the Host ?

Have you tried any other Hosts besides Windows?

[Gowri_M]

Hi

We tried it on windows 10.

[Andrew Neil]

Just one single Win 10 system?

Also, what SD-Card - brand, size, etc ?

Does that card work OK in other places ?

Have you tried other SD Cards?