TUSB8041: Questions for TUSB8041 auto reconnect issue when inserting some brands U-disk

Hi Jacky, 

This should not occur.  If the U-disk has an error, the USB host might reset the entire USB, which would result in this behavior or the power consumption of the U-disk may cause a system VBUS droop resulting in disconnect / reconnect events.

Regards,

JMMN

Hi JMMN,

Thanks for the reply. We checked with customer for more details - this issue only occurred when after TUSB8041 first time powering up with USB2.0 available(their OS is Android, only supports for USB2.0), after the OS successfully reconnected, there will not observe this issue again even plug-in and plug-out the U disk. Another experiment customer did is if you connect another hub after the TUSB8041, you will also not observe such issue.

If we switched the OS to Windows which supports USB3.0, we will also not observe such issue.

Do you have any thoughts for this problem?

Thanks.

Hi Jacky,

Does the reconnect just happen once or repeatedly?  Is battery charging enabled on the hub?

Regards,

JMMN

Hi JMMN,

The reconnect behavior only happens once when powering up, and they enabled the charging control on the hub(PWRCTLx pins have been pulled up) - is this related to the issue?

Attached is customer's schematic, please also help to review if there is any issues could cause this issue.

TUSB8041_Schematic_Customer.pdf

Thanks.

HI Jacky,

Yes, the battery charging function could cause the behavior if the U-disks don't handle the battery charging handshake properly.  What is USB_VBUS of the hub connected to in the system?

Regards,

JMMN

Hi JMMN,

Regarding to the charging enable, we tested that even we disabled it, it also has this behavior, no influence for this issue. The USB_VBUS is connected through 90.9K+10K resistor divider to 5V USB power rail. 

Another phenomenon is when we toggle the GRSTz pin to reset the hub during normal state(Hub has already recognized the U-disk), it will reproduce the similar behavior as powering up reconnect. So looks like this issue is related to hub reset period and afterwards, not sure what's the problem in here.

Thanks.

Hi JMMN,

Any further thoughts for this issue? It is still pending now and customer is waiting for our suggestion.

Thanks a lot!

Hi Jacky,

It looks like the software is doing a soft reset of the hub, but I can't determine why it is occurring.  Can you provide any debug statements from the host controller?

Regards,

JMMN

Hi JMMN,

We could use the TUSB8041 EVM to replicate this issue, and found that when using default EVM jumper settings, when re-connection happens, the PWRCTLx/BATENx pins will be toggled to low(LED D5, D6, D7, D8 will be off for a while on EVM), so it looks like it is related to power detection. Can you help to check if we could disable this power detection feature?

Thanks.

Hi Jacky,

Yes a USB reset sent by the host to the hub over the DP/DM lines would cause the PWRCTLx/BATENx pins to toggle (high -> low -> high).  We need to identify the reason for the extra reset that is not seen by the other hub.   Do you have any access to protocol analyzer tools?

Regards,

JMMN

Hi JMMN,

Sorry for that I don't have any USB analyzer tools in hand, may I know if we can ship customer's board with u-disk to your side to help to check the root cause? It's a little bit urgent now.

Thanks a lot!