TUSB8020B: Interface forum

Hi Mike,

When you are switching the upstream port from USB 2.0 to USB 3.0, does the VBUS (power) to the Microchip devices get cycled?  Do the devices show up if your design is powered on while already connected to the host?  Based on the devices not appearing and the 360 ms pulse, it sounds like the downstream connections are going into USB 3.0 compliance mode.  Do you have an EEPROM or SMBUS host for this application?

Regards,

JMMN

Hello JMMN,

Thank you for your response! Here are your answers:

1) When I change from USB2 to USB3, typically, I power cycle the whole design. On my board, VBUS is supplied by an on-board power supply.

2) If I plug my board into a USB2 upstream port, the LAN7801s show up. If I keep the board powered and change the upstream from USB2 to USB3, the LAN7801s show up as USB2 devices. (but - the 8020 superspeed hub shows up)

3) I agree with the down stream devices being in USB3 compliance mode.

4) I have no EEprom on the 8020 and the SMB bus in not brought out. When I did my last 8020 design, I seem to remember there was a program to get to the 8020 over USB

Thank you again - Mike

Hi Mike,

What do you mean by "program to get to 8020B over USB"?  The only utilities we have to access the TUSB8020B are an EEPROM programming application and an eFuse (OTP ROM) programming application, both require the hub is be in programming mode to access it.

If the downstream connections are getting into compliance mode, there are two possible fixes: one is to adjust the downstream port power timing or reset timing so that the connected devices are not powered on / connected until after the hub and the second is to prevent the hub from entering compliance mode - this can be done by using a EEPROM and setting the dsportECR bit or it looks like it can be set in the OTP ROM too.

If you decide on the second option, I would recommend wiring in an EEPROM with the dsportECR bit set to make sure it addresses the issue before going down the path of setting OTP ROM.

Regards,

JMMN

Thank you JMMN,

Can you tell me what might cause the downstream connection to get into compliance mode.

Right now, I have the hub and the downstream devices on the same POR signal. I will look at delaying the reset to the downstream devices.

If this does not work, I will wire a EEprom to the hub and see if we can disable this mode.

Thank you again for your help!!

Mike

Compliance mode is entered when USB 3.0 polling fails on the first connection attempt.  My guess is that the device or hub is sensing the other's RX terminations early and starting polling before the other, it is difficult to determine exactly what is happening without a scope on the datalines.

Regards,

JMMN

Thank you JMMN,

I have changed resets, and the hub is coming out of reset about 200ms before the downstream devices. Now, USB Device Viewer shows the downstream devices on the SS hub of the 8020, but shows "compliance mode". (I did not see this before making the reset change). Next step is to look at signal integrity on the USB3 traces.

Thank you again for your help!!

Mike

Hi Mike,

Well hopefully that's a step in the right direction in getting everything to stay out of compliance mode reliably

A few other things to try:

• Hub exiting reset after downstream devices
• Toggle VBUS to the USB_VBUS of the hub 
• Toggle VBUS to the downstream devices.

I'll keep the ticket open if you have additional questions/

Regards,

JMMN

Hello JMMN,

I am still having the same USB3 compliance mode issue. I have changed the reset on the 8020 and downstream bridges to be the same. We still have compliance mode.

Question - can we use the 8020 power control signals to drive the VBUS_det signal on the downstream bridge chips? I was thinking that the hub could "control" the downstream bridges this way - what do you think??

Thank you for your help!

Mike

Hi Mike,

As long as the VBUS_det pin  on the device is only a detect input and isn't expecting full VBUS voltage / current levels, it should work.

Regards,

JMMN

Hey JMMN,

The above mod worked much better. The "status" lines on the HUB say that we are connected as USB3 (no compliance mode).

Looking at USB Device Viewer - it says the bridges Failed Enumeration - Unknown USB Device (Link in Compliance mode).

Any thoughts on this? Could this be a descriptor issue?

Thank you for your help!!!

Mike

Hi Mike,

Can you post a screenshot of the usb viewer so I'm clear on what is being reported?  It sounds like the system change is keeping the hub downstream facing ports out of compliance mode, but the upstream facing port of the device is still entering compliance mode.  Is it a firmware based device or hardcoded?

Regards,

JMMN

Good Morning JMMN,

Thank you again for all of your assistance!

Here is a screen shot of what USB Device Viewer is displaying - notice the SuperSpeed Hub - that is the 8020 and the 2 downstream devices are the MicroChip LAN7801's.

The message is that the downstream links are in Compliance Mode, but the status pins on the 8020 do not reflect that condition. (both status pins are at a logic high)

Let me know what you think and Thank you again,

Mike

Hey JMMN,

I have looked at pin 36 on the 8020 - to verify the status of the upstream link. In the above screen shot, all 3 status pins are show connection speed at USB3. (none of the links are in compliance mode)

Any thoughts as to what might be causing this??

Thanks,

Mike

Hey JMMN,

You had said that you could program the 8020 to disable "Compliance Mode". To do this we would have to add a prom - are there instructions for programming the prom??

Thanks,

Mike

Hi Mike,

I just sent you a friendship request, can you accept it and send me a response so I get a notification you accepted?

I can send you a sample EEPROM file and the programming tool.

Regards,

JMMN

Hello JMMN,

When I try to execute the program you sent to me, I get this error message. (No attached TUSB840 device was found. This program will now exit)

Any ideas??

Mike

Error_message.docx

You'll need to force load the driver, I sent you instructions over internal message.

Regards,

JMMN

Hi JMMN,

I have another question about the TUSB8020B hub. The description for pins 21 and 22 say that after reset - these pins indicate the SS connection of downstream port 1 and 2.

My upstream port is USB3 - pins 21 and 22 show logic 1 (meaning the downstream ports are USB3), but, the device tree shows that both downstream ports are in USB2 mode.

Can you give me some insight on how pins 21 and 22 work? They are not showing compliance mode.

Thank you,

Mike

p.s. I have not tried the programming software yet.

Can you me a screen shot of the device tree?  You can send it over direct message if you don't want it on the forum.   These outputs should be based on the internal connect / disconnect status.  I'll need to confirm if compliance mode is reflected as a SS connection or not.

Regards,

JMMN