Xref: utzoo comp.sys.att:4218 unix-pc.general:1355
Path: utzoo!attcan!uunet!van-bc!sl
From: sl@van-bc.UUCP (pri=-10 Stuart Lynne)
Newsgroups: comp.sys.att,unix-pc.general
Subject: Re: Answers to Common 3B1 Questions
Summary: How bad is OBM?
	 Is it hardware or software?
Message-ID: <1875@van-bc.UUCP>
Date: 14 Sep 88 06:26:12 GMT
References: <1709@datapg.MN.ORG>
Organization: Public Access Network, Vancouver, BC.
Lines: 37

In article <1709@datapg.MN.ORG>, sewilco@datapg.MN.ORG (Scot E Wilcoxon) writes:

> 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. 

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!

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. 

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?

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. 


-- 
Stuart.Lynne@wimsey.bc.ca {ubc-cs,uunet}!van-bc!sl     Vancouver,BC,604-937-7532