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Re: Communicating with USB Modem

On Oct 9, 2010, at 10:17 PM, Phil Requirements wrote:

> On 2010-10-09 19:26:42 -0400, Hal Vaughan wrote:
>> On Oct 9, 2010, at 6:49 PM, Camaleón wrote:
> [big snip]
>>> O.k. I also think geting an USB modem to work should just be plug and 
>>> play and no needing to mess with drivers at all. But it could worst: 
>>> there are some embedded modems (those you can find in notebooks) that 
>>> lack of any driver and they render completely useless.
>> Yes, that's true.  And, unfortunately, I had information indicating
>> that any USB modem would be similar to RS-232 in that it'd be
>> plug-n-play.  That's not so.  And, while I'm looking at embedded
>> computers (right now I'm waiting to see if the new Soekris Net-6501
>> will do well for me), at least the modems aren't embedded!  And if I
>> do use Soekris, they have a serial port -- you HAVE to use as a
>> terminal during setup, so once I get the original image created and
>> working, I can copy it to an image file and easily install it on
>> flash cards and just insert it, without using the serial port on
>> each one.  And when they're deployed, I may be able to use it for an
>> RS-232 modem, but I'm not committing to that yet.
> I had an external USB modem that was initially very gratifying, to
> use with a computer that had no serial port. I plugged it in, the
> system found it, and I was online in minutes. No external drivers.
> It was a very nice experience after having spent many hours trying
> to get drivers to work for WinModem cards.

I would think, ideally, a good modem would be like that -- as long as it responds to AT commands properly, then it wouldn't need a driver.

> The one I used was US Robotics, but I can't lay my hand on it right
> this minute to say the product number.

I saw some USR USB modems, but considering how I'll be buying a number of these, and footing the price myself (for various reasons, I can't really pass along this cost to my clients), if the $25 modem I ordered works, I'll be using it over the $45-$50 USR modems.  It's pricing.  Now if they're flaky, then, yes, I'll spend more, but if they work, I won't.

> I did have some problems with this modem over time. The main thing
> I remember is it would get moved from /dev/ttyUSB0 to /dev/ttyUSB1
> occasionally. Or sometimes when the machine was booted the device
> wouldn't get established. I don't know if these were problems with
> the modem or my system.

That's a USB issue.  I ran into that when I was writing my code for controlling the Visteon HD radio (I have a copy of the project on my blog, but the main reason I did it was to turn it over so LinuxICE would have a radio controller).  I had to write a routine that would first check the config file and look for the radio in its last place, then, if needed, send the same signal to every USB device and look for the response.  The only issue is that I was worried the wake-up signal for the radio might crash some devices.  I can't remember why I didn't just scan /proc/bus/usb/devices to get the info.  I think I had to scan the /dev/ttySx devices.  While the radio would USUALLY be at the same place it was last time, sometimes it would move.

> I wanted to point out that the modem I had initially seemed very good
> because of how easy installation was. But that's not the whole story.
> And that there are some plug and play USB modems out there.

I think, for modems, plug and play means that it simply responds to the Hayes command set through a device in /dev.  I'm not sure what you'd set the serial bus speed for in a program like minicom, though.


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