Answers to Common 3B1 Questions

[Robert J. Granvin]

>> The OBM creates tones which confuse some MNP modems and the Telebit Trailblazer.
>> New problem: Your machine will occasionally crash with a "panic: addr fault in
>> kernel" message, but _only_ if you have installed 3.51a _and_ you use the OBM
>> (On Board Modem).  If you use a modem attached to any serial port, you'll never
>> see the problem.
 
>I'm just porting my serial driver to the 3b1 (aka Unix-pc) for a client who
>wants bi-directional use of the serial port (allow incoming and outgoing
>calls without mucking about with /etc/inittab) with a Telebit Modem. 
>
>The above comments makes me wonder whether supporting the OBM as well is 
>worthwile. 

It depends where you are going with this driver.  For the client, it
may not be an issue or even a desire.  If you're every going to make
it available to the net at large, or to others in some fashion, you
probably ought to consider supporting it.
 
>I've not used the 3b1 very much (first saw one on Friday). But delving into
>the kernel shows that supporting the OBM will be a royal pain. AT&T (or CT)
>saw fit to have two drivers, one for the serial port, and one for the modem,
>but sharing some common code by direct calls. You can't just replace the
>serial driver with loadable driver and have the phone driver use it!

Fun how they did that... :-)

>There seem to be two separate problems with the OBM. First it has slightly
>incompatible tone generation. Second there seems to be some problem with
>kernel panic's. 

The tone problems will more than likely never be repaired.  The kernel
panics, on the other hand, are supposed to be fixed in the next fix
disk release, which is still known as "3.51b".  Some hotline techs are
now aware of its existance, but they're also aware that it hasn't been
released yet, and no date has been announced.  However, with ATT
history, it'll probably not be announced, just suddenly appear.

Therefore, you shouldn't worry about the kernel panics for the future,
but if the tone problems are an issue, they will stay one.

>So the question is, is it worthwhile to support the OBM or just to utilize the 
>standard serial port (or expansion slot port) with an external modem?

For general purpose, people like to have everything supported.  Most
people immediately dump the OBM when they install a replacement modem
on the machine.  There are only a few people I know who are still
using the OBM exclusively, and a small number of people use the OBM as
a backup to their attached modem for outdial. 

So, if you're thinking general purpose, you might as well make an
attempt to support it.  If it's just for a client, discuss it with
him/her and see if they care.

>I've got the driver up and it works well for the standard port. Should be
>able to knock of the expansion slots tomorrow. So I'd appreciate any
>feedback on how people actually use these machines, and what works best. 

See above.  :-)

These impressions are based solely on personal experience on how
people I know have used their 3b1/7300's.  Fortunately, that number
isn't small (except perhaps to colleges with bazillions of them, or
ATT :-)

-- 
                                                             Robert J. Granvin
"Martyrs are just dying                     National Information Systems, Inc.
 to be heroes."                                              rjg at sialis.mn.org
                                  ...{{amdahl,hpda}!bungia,rosevax}!sialis!rjg