mtntop

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Kernel version: 2.6.21.4

We are getting an issue with the USB modem we are using. The modem seems to become "corrupt" somehow and stops working.

We've found that unplugging the modem and plugging it back in fixes the problem. But *rebooting the computer* doesn't.

By 'reboot' I mean a soft reboot.

Why is this? I assumed rebooting would have the same effect as unplugging the modem.

My own guess is that the problem is internal to the modem, and the modem needs to lose all power to 'reset' itself. A soft reboot maintains power to the modem, so the modem does not get reset. Is this true?

So how can we duplicate the effect of unplugging a usb device, without actually doing so?

We want to install these machines remotely and want to resolve this problem (and any other potential problems with the modem) remotely, without physical access to the machine. So unplugging is not a practical solution in production.

I haven't tried a hard reboot to see if this behaves differently. The problem is intermittent and hard to reproduce.

Thanks for any insight into how linux works.

exvor

Some motherboards like my Asus board retain power on the USB ports after the system goes down and even while the system is off. I use this rather nice feature to charge my cell. Some motherboards do not. The ECS board in my room computer is an example of such. Sometimes its only the front ports sometimes its only the back ports. As for the modem you can try and compile the driver as a module instead of a built in kernel driver. That resolves problems I have with sound cards sometimes.

mtntop

Thanks exvor. You are right; even when I shutdown the computer, the light on the modem is still shining. I have to unplug the AC power before the light goes off. We are using an EeePc. I've tried the different USB ports but they all have power when the OS is shutdown.

It looks like I'll have to try to either power down the USB port through the OS (I've searched for posts on this and it doesn't look easy) or perhaps look for a way to tell the modem to reset itself.

exvor

It might be possible via UART commands if modems even use them these days <.< >.> its been a long long times since ive messed with one.