I found the reason.

Power-off on PC was the problem.


So, I got rid of my serial cable on pc,
and changed /etc/ttys,
and patched nvRAM.

My laziness:  I found similar situation at
(http://www.netbsd.org/Ports/sparc/faq.html)
Whenever I unplug the serial console, my machine reboots! (top)
A continuous stream of zeros is equivalent to a "BREAK" command
which will enter the prom.
This might happen, since the serial lines are floating when you unplug
your cable. If you build a special switchbox that uses a pullup
resistor, then you can avoid this problem.
Put a 4.7 KOhm resistor between pins 3 and 25.


I'll use only tcp/ip VT.

But, I hope using serial console for secure tty also. :-)
If I knew anything about serial port driver,
I would have fixed this. I have to study more and more.

When I met NetBSD 2 months ago, patching nvram made
my crt show check flag at edge(F1 racing check flag style).
It's why I didn't patch nvRAM.
Today I first met spots, but after 2 hours, making mac auto-boot,
Spots had gone. weird things always happen. :-)


+--- my changes.
(1) /etc/ttys

console "/usr/libexec/getty std.38400"  vt100   on secure
#ttyE0  "/usr/libexec/getty std.9600"   vt100   on secure
tty00   "/usr/libexec/getty std.38400"  vt100   on secure
tty01   "/usr/libexec/getty std.38400"  vt100   off secure

(2) nvRAM patch (Guru method described at FAQ).
(3) set input-device kbd; \ set output-device /chaos/control.

Thanks for your all help.

Bill worte:

2) If you unplug the serial cable regularly (like when it's not in use),
you probalby want to do a little wiring surgery. Get a resistor, like
47k
Ohms, and wire it between the receive data input and the DTR pin. When
the
other computer is sending data, this resistor will do nothing (at worst
it
will draw half a milliamp of current). But when the other computer is
not
there, the resistor will keep the receve data pin at the voltage level
for
a '1' bit. Then you won't see a spurrious BREAK sequence.




----- Original Message -----
From: "Inseo Park" <bubux@krpost.net>
To: <port-macppc@netbsd.org>
Sent: Friday, July 26, 2002 7:04 PM
Subject: db> message after some hours (using Serial Console only)


> I tried NetBSD 1.6 BETA4 on my PowerMac 7300/180.
>
> but after some hours, (disconnected all terminal)
> when I tried to connect NetBSD via serial console
> I get db> prompt and I must type continue to run.
>
> What is db> ? is that kernel debug mode?
> is that a message of "sleeping mode?"
>
> I want NetBSD to run as a server (DB, WEB, Samba).
> and with db> message all server are went down.
>
> How can I run NetBSD without any ttys/console connected?
> Because, sometimes PC connected with serial line
> must be shut down, with other workstation running.
>
> What log file should I examine?
>
> If any documents related about this,
> please let me know.
>
> My setting:
> NetBSD 1.6 BETA4
> with sys.src.tgz kernel patched
> dmesg:
> NetBSD 1.6D (MACBSD_GEN) #0: Wed Jul 24 03:05:54 KST 2002
>     bubux@macbsd:/usr/src/sys/arch/macppc/compile/MACBSD_GEN
> total memory = 144 MB
> avail memory = 123 MB
> using 1868 buffers containing 7472 KB of memory
>
> because I am using Sonnet Tempo ATA-100 Card.
> (my SCSI HDD is all broken, and SCSI HDD is too expensive in korea)
>
> I just configured kernel like faq (to setting boot device manually).
>
> I didn't patched open firmware (except real-base, load-base),
> because I am using it via serial-console on my Windows PC.
> (Original console doesn't support Hangul but virtual terminal
> with Netterm I can write hangul).
>