iMX6 - Enable USB OTG port without VBUS connected

[simon_willis]

Hi All,

We are trying to bring-up our first  iMX6ULL prototype board. Unfortunately, USB is not being enumerated in Windows, so we cannot use mfgtools. I think the reason for this is because we have forgotten to connect USB_OTG1_VBUS and my understanding of the USB controller is that it uses VBUS to detect a device is connected. Is there any way I can work around this using a JTAG to force the USB into OTG device mode? I have been trying various things to force the USB registers, but have so far been unsuccessful. Any help would be greatly appreciated.

Regards,

Simon

[Rita_Wang]

If you want to use the OTG port as host, you must supply the 5V to VBUS pin.

In the EVK use case,

The OTG1 is OTG port, the ID pin controls the host and device function selection and the VBUS pin is used for connection detection. The OTG2  is host port, so the VBUS pin is always powered.

[simon_willis]

Hi Rita,

Thanks for this reply. It is very helpful. Unfortunately, my current PCB does not have the VBUS pin exposed, so I am not able to connect a voltage to it. We will fix the next version of the design. In the interim, is there a way, I can force the CPU into OTG device mode with the JTAG so that I can load firmware via mfgtools? At the moment I am quite stuck and unable to load Uboot to the onboard eMMC chip.

Regards,

Simon

[Rita_Wang]

I have discuss with our exert and collegue, for the JTAG download we do not have tool for it, and do not recommend to use it.

[simon_willis]

Thanks Rita. Unfortunately USB_OTG2_VBUS is also not connected. This will be fixed in the next board revision, but I'd like to be able to do testing of some of the other hardware on this current PCB. My only options at the moment are JTAG and RS232 on UART1.

I'm hoping I can load the U-boot binary into RAM via the JTAG and then execute it. After that, I should be able to load the image into the eMMC. It's not ideal, but I think it's my only option at the moment. I'd appreciate any ideas you might have.

[Rita_Wang]

Hi Simon,

Yes, I see your design, you can not use the usb otg port. Here the only method you can try is your above idea, the same the method I recommend you. You need to load the u-boot. Do you have the Nor flash or QSPI in your board? If yes, you can try to download the u-boot to nor falsh and boot up u-boot. If u-boot work well you can load images to emmc.

But if it can not work, you have to wait for your next version board.

Hope it can do some help for you.

Have a nice day

Rita

[Rita_Wang]

How about your USB_OTG2_VBUS? Does it connect the 5V? If yes, the otg1 also can work, the USB_OTG1_VBUS and USB_OTG2_VBUS supply the 5V to LDO_USB and then give 3.0V to PHY. Here you can send your CPU usb connection and usb connector section schematic to me, I can see if it can work.

[simon_willis]

This is what we have unfortunately.

[mrudangshelat1]

Hi Simon,

Kindly check boot mode resistor settings for your system. I guess will enumerate the A7 port first to flash the i.MX6ULL.

Please use different USB ports, different PCs and Laptops and check. make sure you connect the USB-UART TX, RX and GND while checking with mfgtools. We also faced similar issue but solved with the above explanation. Also do instant plugin for USB after USB-UART interfaces with PCs/Laptops.

Mrudang