single USB VBUS USB2 not working correctly

forumuser · ‎08-03-2017

We have a custom board running Linux with USB1 used as external USB interface and USB2 used to connect a 3G/4G Modem.

Only USB_VBUS1 is connected to 4.7V, VUSB_CAP is at 3.2V.

In this situation the 3G/4G modem (high-speed device) does not enumerate in Linux environment.

When forced to enumerate again it is detected as full-speed device and not working properly.

usb 2-1: new full-speed USB device number 2 using ci_hdrc
usb 2-1: device no response, device descriptor read/64, error -71
usb 2-1: device no response, device descriptor read/64, error -71

When the voltage at USB_VBUS1 is increased to 4.9V it enumerates correctly.

When the modem is connected to USB1 it enumerates correctly.

usb 1-1: new high-speed USB device number 2 using ci_hdrc
option 1-1:2.2: GSM modem (1-port) converter detected
usb 1-1: GSM modem (1-port) converter now attached to ttyUSB0
option 1-1:2.3: GSM modem (1-port) converter detected
usb 1-1: GSM modem (1-port) converter now attached to ttyUSB1
option 1-1:2.4: GSM modem (1-port) converter detected
usb 1-1: GSM modem (1-port) converter now attached to ttyUSB2
option 1-1:2.5: GSM modem (1-port) converter detected
usb 1-1: GSM modem (1-port) converter now attached to ttyUSB3

In uboot the device is detected correctly on USB2:

=> usb tree
USB device tree:
1 Hub (480 Mb/s, 0mA)
u-boot EHCI Host Controller

2 Hub (480 Mb/s, 0mA)
| u-boot EHCI Host Controller
|
+-3 Vendor specific (480 Mb/s, 500mA)
HUAWEI Technology HUAWEI Mobile 0123456712ABCA17

I'm running out of ideas here so any suggestion is welcome.

Best regards,

Ralf

CarlosCasillas · ‎08-05-2017

Hi Ralf,

If you are using an i.MX6 processor with NXP BSP, you could refer to the SABRE schematic on the USB part.

Considering a custom hardware, you could refer to the USB-related sections of the following documents:

http://www.nxp.com/docs/en/user-guide/IMX6DQ6SDLHDG.pdf

http://www.nxp.com/docs/en/application-note/AN4589.pdf

http://www.nxp.com/docs/en/application-note/AN4136.pdf

Hope this will be useful for you.
Best regards!
/Carlos
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forumuser · ‎08-07-2017

Hi Carlos,

i didn't mention that i'm using an i.MX6UL, my bad.

Nevertheless none of the documents you are referring to gives me any hint on why changing VUSB would have any influence (as long it is between 4.4V and 5.5V).

Best regards,

Ralf

CarlosCasillas · ‎08-07-2017

Hi Ralf,

So, you could refer to the “Hardware Development Guide for the i.MX 6UltraLite Applications Processor” document, available at the following link:

http://www.nxp.com/docs/en/user-guide/IMX6ULHDG.pdf

Regarding the voltage levels of Vbus, you should refer to the “Universal Serial Bus Specification” document from usb.org website, as Vbus minimum allowed voltage is different for a strand port and low-power hub port.

You could also use as reference the schematic of the i.MX6UL EVK board, which have one OTG port and one standard-A Host port.

Hope this will be useful for you.
Best regards!
/Carlos
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Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

forumuser · ‎08-08-2017

Hi Carlos,

i used the EVK as base for my hardware development and my USB schematic is quite similar to the EVK. USB_VBUS is used only to supply the i.MX6UL USB block, supply voltage for external USB devices is generated seperately. The 4G modem doesn't require USB_VBUS and is working perfectly on USB1 (with some weird manually drawn wiring) but not on USB2 (correctly routed differential pair) unless i increase the voltage at USB_VBUS to at least 4.9V.

Best regards,

Ralf