Re: No /dev/modem or similar created on PowerPC?

[Rick Thomas <rbthomas55@pobox.com>]

On Friday, September 17, 2004, at 03:12 PM, Joey Hess wrote:

> Russell Hires wrote:
> > I'm just poking around on my G3/266 and I'm noticing that I don't 
> > have a
> > /dev/modem, or any tty that links to it. Does the d-i create such a
> > device only if you say that you want to install via ppp? This 
> > could be a
> > problem if, for example, you want to use your modem to output a serial
> > console (which is my situation, actually :-) In fact, I can't 
> > find (and
> > neither can kppp) which tty connects to my modem.
>
> d-i does not know about modems. I think that pppconfig might set a
> /dev/modem link if you choose to use it to install via modem in
> base-config, but in general yes, new installs have no /dev/modem link.
> Probing for modems is a rather risky business that has been known to
> turn off UPSes and do other fun stuff, I don't think the installer 
> wants
> to go there.
>
> I don't understand what a modem has to do with a serial console BTW.

I think I can clear up a point or two here.

OldWorld Macs have two serial RS-232 ports (actually RS-422, but 
who's counting?) one is marked "Printer" and the other is marked 
"Modem".  In at least some models, the "Printer" port did not have 
the RS-232 modem flow-control signals enabled, but the "Modem" port 
did -- hence the distinction and the naming convention.

Russell is probably *not* talking about using an actual real-live 
modem.  What he's probably talking about is the fact that the Mac 
Open Firmware sometimes uses the "Modem" port as a serial console.  
In order to see the stuff that appears on that line, you need to 
use a serial cross-over cable (also -- confusingly -- called a 
"null-modem" cable) to connect the "Modem" port to another machine 
running a terminal emulator (such as macKermit) or an actual 
real-live terminal from the dark ages.

To answer the question Russell is probably asking:  The "Modem" 
port is called "/dev/ttyS0".  You didn't ask, and you could 
probably figure it out for yourself, but just for completeness, the 
"Printer" port is called "/dev/ttyS1".  Note the upper-case "S".

I've never been able to make it work, but I'm told that when you 
use kernel boot-time command-line arguments to tell the booting 
kernel to send it's messages to the serial console port, you should 
leave off the "/dev".  Thus: "console=ttyS0"


Hope this helps!

Rick