MC8795V USB device connect/disconnect loop under Linux

IoT Modules MC/EM Series
1

I’ve been working with Sierra support on the following issue with no resolution so far, has anyone else seen this behaviour:

Steps to reproduce:

  • Insert an AT&T or T-Mobile SIM into an MC8795V in its factory state
  • Attach the MAIN antenna
  • Insert the module into a Ubuntu 9.04 system
  • The USB device starts flapping between connected and disconnected, log below
[4764278.940024] usb 1-7: new high speed USB device using ehci_hcd and address 107
[4764279.086781] usb 1-7: configuration #1 chosen from 1 choice
[4764279.092083] sierra 1-7:1.0: Sierra USB modem converter detected
[4764279.096594] usb 1-7: Sierra USB modem converter now attached to ttyUSB0
[4764279.096766] sierra 1-7:1.1: Sierra USB modem converter detected
[4764279.097596] usb 1-7: Sierra USB modem converter now attached to ttyUSB1
[4764279.097834] sierra 1-7:1.2: Sierra USB modem converter detected
[4764279.098613] usb 1-7: Sierra USB modem converter now attached to ttyUSB2
[4764279.098829] sierra 1-7:1.3: Sierra USB modem converter detected
[4764279.102259] usb 1-7: Sierra USB modem converter now attached to ttyUSB3
[4764279.102511] sierra 1-7:1.4: Sierra USB modem converter detected
[4764279.103218] usb 1-7: Sierra USB modem converter now attached to ttyUSB4
[4764279.103422] sierra 1-7:1.5: Sierra USB modem converter detected
[4764279.104673] usb 1-7: Sierra USB modem converter now attached to ttyUSB5
[4764279.104967] sierra 1-7:1.6: Sierra USB modem converter detected
[4764279.105680] usb 1-7: Sierra USB modem converter now attached to ttyUSB6
[4764287.236627] usb 1-7: USB disconnect, address 107
[4764287.236896] sierra ttyUSB0: Sierra USB modem converter now disconnected from ttyUSB0
[4764287.236919] sierra 1-7:1.0: device disconnected
[4764287.237111] sierra ttyUSB1: Sierra USB modem converter now disconnected from ttyUSB1
[4764287.237132] sierra 1-7:1.1: device disconnected
[4764287.237318] sierra ttyUSB2: Sierra USB modem converter now disconnected from ttyUSB2
[4764287.237338] sierra 1-7:1.2: device disconnected
[4764287.237540] sierra ttyUSB3: Sierra USB modem converter now disconnected from ttyUSB3
[4764287.237561] sierra 1-7:1.3: device disconnected
[4764287.237760] sierra ttyUSB4: Sierra USB modem converter now disconnected from ttyUSB4
[4764287.237781] sierra 1-7:1.4: device disconnected
[4764287.237978] sierra ttyUSB5: Sierra USB modem converter now disconnected from ttyUSB5
[4764287.237999] sierra 1-7:1.5: device disconnected
[4764287.238198] sierra ttyUSB6: Sierra USB modem converter now disconnected from ttyUSB6
[4764287.238219] sierra 1-7:1.6: device disconnected
[4764293.980023] usb 1-7: new high speed USB device using ehci_hcd and address 108
[4764294.114748] usb 1-7: configuration #1 chosen from 1 choice
[4764294.121072] sierra 1-7:1.0: Sierra USB modem converter detected
[4764294.122506] usb 1-7: Sierra USB modem converter now attached to ttyUSB0
[4764294.122656] sierra 1-7:1.1: Sierra USB modem converter detected
[4764294.123124] usb 1-7: Sierra USB modem converter now attached to ttyUSB1
[4764294.123278] sierra 1-7:1.2: Sierra USB modem converter detected
[4764294.123881] usb 1-7: Sierra USB modem converter now attached to ttyUSB2
[4764294.128728] sierra 1-7:1.3: Sierra USB modem converter detected
[4764294.129675] usb 1-7: Sierra USB modem converter now attached to ttyUSB3
[4764294.129898] sierra 1-7:1.4: Sierra USB modem converter detected
[4764294.130729] usb 1-7: Sierra USB modem converter now attached to ttyUSB4
[4764294.130924] sierra 1-7:1.5: Sierra USB modem converter detected
[4764294.132269] usb 1-7: Sierra USB modem converter now attached to ttyUSB5
[4764294.132484] sierra 1-7:1.6: Sierra USB modem converter detected
[4764294.134389] usb 1-7: Sierra USB modem converter now attached to ttyUSB6
[4764302.329615] usb 1-7: USB disconnect, address 108
[4764302.330074] sierra ttyUSB0: Sierra USB modem converter now disconnected from ttyUSB0
[4764302.330097] sierra 1-7:1.0: device disconnected
[4764302.330291] sierra ttyUSB1: Sierra USB modem converter now disconnected from ttyUSB1
[4764302.330312] sierra 1-7:1.1: device disconnected
[4764302.330501] sierra ttyUSB2: Sierra USB modem converter now disconnected from ttyUSB2
[4764302.330520] sierra 1-7:1.2: device disconnected
[4764302.330746] sierra ttyUSB3: Sierra USB modem converter now disconnected from ttyUSB3
[4764302.330764] sierra 1-7:1.3: device disconnected
[4764302.330967] sierra ttyUSB4: Sierra USB modem converter now disconnected from ttyUSB4
[4764302.330988] sierra 1-7:1.4: device disconnected
[4764302.331183] sierra ttyUSB5: Sierra USB modem converter now disconnected from ttyUSB5
[4764302.331204] sierra 1-7:1.5: device disconnected
[4764302.331406] sierra ttyUSB6: Sierra USB modem converter now disconnected from ttyUSB6
[4764302.331426] sierra 1-7:1.6: device disconnected

When I detach the antenna, the module connects and stays connected - and I can send AT commands.

This issue does not occur inserting the same module into a Windows 7 system running Sierra Watcher. When the module is removed from the Windows 7 system and reinserted into the Ubuntu 9.04 system, the problem is gone.

I’ve tried multiple modules, reflashing firmware and the latest Sierra USB modem driver (1.7.30) with no success.

I’ve also tried using the generic usb-serial driver (modprobe usb-serial vendor=0x1199 product=0x683c), which exhibits the same symptoms.

Cheers.

2

On which kind of device (Notebook, Embedded hardware, Developer board, etc.) did you use the minicard module?

3

Hiya
Our customer also have this problem for SL8082 modules in Kernel 2.6.21, the driver version is 1.7.36, I think it may be the power supply issue, the voltage is 3.3v, I let the HW engineer to mofify the design first.

4

After power supply is ok, this problem is solved

5

One of a hell tricky situation can be with similar symptoms if the card is not plugged in the socket correctly!

6

We are experiencing the exact same issue. All the modems are MC8790V with firmware K2_0_7_35AP. The USB disconnects very clearly seem to happen only when the modem is using a 2G network connection, but not every 2G connection results in USB disconnects. We tried two different mobile carriers, their 2G networks are both operating on the 900MHz GSM band.

When we force the modem to use 3G only (either via !SELRAT or +COPS=…,2) there are no disconnects. We have a development prototype with a different firmware (K1_1…) that does not show this behavior.

The disconnects happen as soon as the modem is powered up and has a PIN free SIM inserted. There is no usbserial or sierra driver involved, just the ohci-hcd USB hub driver needs to be loaded to power up the USB. It even happens on a Windows XP laptop.

7

This is happening to me using the Sierra Wireless Watcher on Windows 7. It is very strange.

8

Hello all together,

sorry about my bad english but we had the same symptoms on a sierra wireless demoboard with a MC8790V.
Final solution was replacing the supercap on the demoboard by high capacity MLCC’s.
As you can read in the hardware integration guide

…
At maximum GSM transmit power, the input current can
remain at 2.4 A for up to 25% of each 4.6 ms GSM cycle
(1.15 ms) after initially reaching a peak of 2.75 A average over
100 μs and with an instantaneous peak current of 3.5 A.
…

the power supply must be capable to provide these current during a GSM burst without a ripple more than 100 mV. When powering e.g. from USB-Port (or even 2 USB-Ports) there is a need for one (or more) high capacity capacitor with low ESR.
But derating (because of age / temperatur / stress ) causes loss of capacity so ripple increase beyond limit causing modem to do power-fail reset. This only can happen when using 2G modes because 3G/4G modes do not need burst like that.
Obviously the same situation occure if there is a contact resistance between module and power supply.

So my hint is exchange capacity or better increase capacity beyond recommendation to compensate aging and try to minimize line or contact resitance.

Regards,
Andy