STM32U575 USB MSC issues

[tvarghese]

Hello All,

On the STM32U575 is there any guidance regarding use of external resistors?  I don't see any on the reference design so I didn't put it on my board either.  USB data rates are fairly slow, is impedance matching even required?

We are using TinyUSB so that we can avoid the RTOS and it works fine mostly, but occasional USB disconnects.

We discovered by accident using a longer cable seems to resolve this. I am wondering if it is a fluke or if there is some rational reason for this.

Thanks!

[Gyessine]

Hello @tvarghese 
TinyUSB is not supported by STMicroelectronics 
but can you see how much data rate are you getting?
I recommend using ST official stack. Here is an MSC example based on STM32U575 that you can use as reference.
BR
Gyessine

[tvarghese]

Don't want the RTOS.  Thanks.

[tvarghese]

Tried 22 ohm resistors, made things even worse. But with the longer cable it seems to still work.

[Gyessine]

Hello @tvarghese 
You can use the MSC class in standalone mode with STM32U575.
RTOS is not a mandatory requirement.
Some work needs to be done, but it is possible.
Here are some USB projects completed with STM32U575 using standalone mode (no RTOS used).
If these examples are not sufficient, there are articles that can help you 
-How to implement USB mass storage device standalon... - STMicroelectronics Community 
-How to implement USBX in standalone mode - STMicroelectronics Community
-How to use STMicroelectronics classic USB device m... - STMicroelectronics Community

BR
Gyessine