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Old 02-09-2007, 02:03 PM   #1
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Registered: Oct 2005
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Unhappy /dev/ttyS0 on nc6000 not working

Hi, I have a HP compaq nc6000 laptop and I want to use the serial port
to connect to other computers and use kermit or minicom. Unfortunately,
it doesn't work. The seems to be blocked or broken in some way. It
works fine under WinXP. It also works on my desktop under FC6 but not on
the nc6000. And it also works under Solaris (Belenix) on the nc6000.
But not under FC6. This implies a problem with linux.

The laptop is running Fedora Core 6 (and will also boot WinXP). The
kernel version is:

Linux version 2.6.19-1.2895.fc6 ( (gcc version 4.1.1 20070105 (Red Hat 4.1.1-51)) #1 SMP Wed Jan 10 19:28:18 EST 2007

The serial port is detected during boot-up as indicated by:

# grep tty dmesg
serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
serial8250: ttyS2 at I/O 0x3e8 (irq = 3) is a 16550A
00:02: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A

If I look in /sys/devices/pnp0/00:02 I see:

# ls
bus driver id options power resources subsystem tty:ttyS0 uevent


# cat resources
state = active
io 0x3f8-0x3ff
irq 4

This info is identical to what WinXP's hardware manager gives.

Also, /proc/tty/driver/serial gives:

# cat /proc/tty/driver/serial
serinfo:1.0 driver revision:
0: uart:16550A port:000003F8 irq:4 tx:0 rx:0 CTS|DSR|CD|RI
1: uart:unknown port:000002F8 irq:3
2: uart:16550A port:000003E8 irq:3 tx:0 rx:0 CTS|DSR|CD|RI
3: uart:unknown port:000002E8 irq:3

and setserial gives:

# setserial -a /dev/ttyS0
/dev/ttyS0, Line 0, UART: 16550A, Port: 0x03f8, IRQ: 4
Baud_base: 115200, close_delay: 50, divisor: 0
closing_wait: 3000
Flags: spd_normal skip_test

If I run lsmod I see the "serio_raw" module only and no module called
"serial" or "8250" (although 8250 is listed in /sys/modules). I also only
see "serio_raw" on my desktop which works!

It looks like its there but if I run kermit and do "set line" it says that
/dev/ttyS0 is not a terminal device. e.g.:

# kermit
C-Kermit 8.0.211, 10 Apr 2004, for Red Hat Linux 9.0
Copyright (C) 1985, 2004,
Trustees of Columbia University in the City of New York.
Type ? or HELP for help.
(/root/) C-Kermit>set line /dev/ttyS0
/dev/ttyS0 is not a terminal device
Connection to /dev/ttyS0 failed:
(/root/) C-Kermit>set line

After this I get a line in /var/log/messages:

Feb 9 11:50:33 localhost kernel: ttyS0: LSR safety check engaged!

as if it can't see the registers on the serial device.

Question: Am I missing something? or is linux serial ports broken on this
laptop? Any ideas?

Old 02-12-2007, 07:02 AM   #2
Registered: Dec 2006
Location: Bracknell, UK
Distribution: SUSE 13.1
Posts: 159

Rep: Reputation: 33
You've probably Googled this already, but it appears that others are having trouble with the serial ports on nc6000 kit. See

They mention that booting another distro (eg. a live distro disk) gets the serial ports working fine, so it's probably a driver problem combined with the particular h/w in the nc6000 (a wild guess, but... it does happen!).

If that's true, it's frustrating! You could try re-building the serial module with a source update from the latest kernel (or the version on whatever live distro works) and just replace that one module. As long as the versions aren't very different, that might work.

Old 02-12-2007, 08:53 AM   #3
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Registered: Oct 2005
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Thanks for the reply. I checked out the link you gave and it looks like the same problem. Seems
to be a bug in the kernel driver. Sigh!

Old 02-23-2007, 09:11 AM   #4
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Registered: Oct 2005
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Seems the bug is in the acpi code. Setting acpi=off or acpi=ht in the kernel parameters in grub.conf
causes the serial port to work.
Old 02-26-2007, 09:45 AM   #5
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Registered: Oct 2005
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Original Poster
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An even better fix. Set pnpacpi=off in the kernel boot parameters in grub.conf. Then the
volume control buttons work as well as the serial port! Cool.


fc6, serial port

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