MC7455 USB device disconnects immediately

Hello,

I am working on an IOT product, where we are planning to use Sierra MC7455 chip as an LTE Modem and also for GNSS. We are using Yocto based build system, so I could configure the Linux Kernel and build again.

The kernel version used is 4.9.39. I have enabled the Sierra Wireless config for USB_Serial in kernel config. After turning on the system I could see that the chip keeps on connecting and disconnecting immediately. The logs are as follows:

qcserial 1-1.3:1.0: device disconnected
usb 1-1.3: new high-speed USB device number 23 using ci_hdrc
usb 1-1.3: New USB device found, idVendor=1199, idProduct=9070
usb 1-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 1-1.3: Product: Sierra Wireless MC7455 Qualcomm
usb 1-1.3: Manufacturer: Sierra Wireless, Incorporated
usb 1-1.3: SerialNumber: LQ71660082041020
qcserial 1-1.3:1.0: Qualcomm USB modem converter detected
usb 1-1.3: Qualcomm USB modem converter now attached to ttyUSB0
usb 1-1.3: USB disconnect, device number 23
qcserial ttyUSB0: Qualcomm USB modem converter now disconnected from ttyUSB0
qcserial 1-1.3:1.0: device disconnected
usb 1-1.3: new high-speed USB device number 24 using ci_hdrc
usb 1-1.3: New USB device found, idVendor=1199, idProduct=9070
usb 1-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 1-1.3: Product: Sierra Wireless MC7455 Qualcomm
usb 1-1.3: Manufacturer: Sierra Wireless, Incorporated
usb 1-1.3: SerialNumber: LQ71660082041020
qcserial 1-1.3:1.0: Qualcomm USB modem converter detected
usb 1-1.3: Qualcomm USB modem converter now attached to ttyUSB0
usb 1-1.3: USB disconnect, device number 24
qcserial ttyUSB0: Qualcomm USB modem converter now disconnected from ttyUSB0
qcserial 1-1.3:1.0: device disconnected

Please let me know, how to solve this issue. I have libqmi installed from the Yocto build. I have also flashed the latest firmware from Sierra - 9999999_9904609_SWI9X30C_02.24.03.00_00_GENERIC_002.021_000.exe

Thanks & Regards,
Vinothkumar

Vino,

I cannot really tell you why this would be doing it but I would STRONGLY recommend that you use our GobiSerial and GobiNet drivers, the open source ones are used widely as is qmilib but they can have unpredictable behaviour which is why we have our own (and our own equivalent of qmilib).

Regards

Matt

The modem is looping in bootloader mode without ever enumerating in application mode. It’s unlikely that drivers, or any other part of the host sotware or hardware, makes any difference. The bootloader should eventually enter failsafe mode where the ramdump tool from the SDK can be used to help analyzing the crash. I recommend using SWI support for this.

Hi,

I have an update. I tried to use USB to mini-PCIe convertor. Surprisingly, if I connect to my hardware using USB to mini-PCIe, the chip is getting identified and is working fine. But if I tried to connect to the PCIe slot its not working, the device gets disconnected immediately and is trying to connect again.

Not sure whats happening , do you have any suggestion.

Regards,
Vinothkumar

Vino,

Are you plugging this into a PCIe slot on a laptop? If so then the PC OEM’slock these down pretty hard as it is for their use only, it will probably be a secret setting somewhere in the BIOS. Can’t help you there.

Regards

Matt

Hi,

No. I am using an embedded hardware from Compulab.

compulab.com/products/comput … /#overview

I have used the pcie slot with TELIT chips, it worked fine.

Regards,
Vinothkumar

I assume the slot on the board is configured for PCIe and not USB3 SS? Did you cover the USB3 TX/RX pins on the modem? If not, then try that.

Hi,

I tried masking the USB pins (USb3 Tx and RX pins) . I have attached the image.

Still I am facing the same issue when I connect the module over PCiE. The device enters into boot mode and loops repeatedly.

qcserial ttyUSB0: Qualcomm USB modem converter now disconnected from ttyUSB0
qcserial 1-1.3:1.0: device disconnected
usb 1-1.3: new high-speed USB device number 26 using ci_hdrc
usb 1-1.3: New USB device found, idVendor=1199, idProduct=9070
usb 1-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 1-1.3: Product: Sierra Wireless MC7455 Qualcomm
usb 1-1.3: Manufacturer: Sierra Wireless, Incorporated
usb 1-1.3: SerialNumber: LQ71660022021020
qcserial 1-1.3:1.0: Qualcomm USB modem converter detected
usb 1-1.3: Qualcomm USB modem converter now attached to ttyUSB0
usb 1-1.3: USB disconnect, device number 26
qcserial ttyUSB0: Qualcomm USB modem converter now disconnected from ttyUSB0
qcserial 1-1.3:1.0: device disconnected

Any info on the topic would be helpful.

Regards,
Vinothkumar

Vino,

I think you need to check the full pin out of the PC board you are using and compare it to the MC74 one. there may be some other incompatibility.

Regards

Matt

Hi,

After lot of tries with masking the pins, I could succesfully connect the MC7455 to my system using PCIe.

I have masked the following pins:

USB3 masking -> Pin 23,25,27,29,31,33

and also the following pins:

Pin 20 - W_DIABLE_N
Pin 22 - SYSTEM_RESET_N
Pin 24 - Vcc

I am not sure why masking these pins are necessary. Any information on side effects of masking these pins would be helpful.

Regards,
Vinothkumar

Regards,
Vinoth

Vino,

If the pins are in the wrong level or the unit is detecting activity on then not consistent with USB 3.0 then it causes issues with enumeration of the unit to the host.

Regards

Matt