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Old 05-13-2011, 01:04 PM
Tapio Lehtonen
 
Default How to use serial ports?

I try to connect two pc hosts with serial ports with a null modem cable.
I assumed starting kermit on both ends, setting line, speed etc. to
suitable values would allow me to see what I type on the other end. But
no such luck.


I admit it is 9 years since I last used serial ports for anything, but
at those far away times I got them working. Is there now something that
must be set up or turned on to use serial ports?


I use Debian GNU/Linux Squeeze, ckermit. I tried also with gtkterm to
rule out ckermit as the not working part.


Tapio Lehtonen


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Old 05-13-2011, 03:05 PM
Frank Miles
 
Default How to use serial ports?

Serial ports can be pretty opaque.

Do you know if both serial ports were enabled in your BIOS? Can you find out if the relevant ports appear enabled in the system logs?

Do you have any hardware diagnostic tools? i.e. one of those LED-based serial port monitors?

Do you have flow control (RTS/CTS) disabled?

HTH...


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Old 05-13-2011, 04:48 PM
Tapio Lehtonen
 
Default How to use serial ports?

Did not check BIOS for port settings, I supposed ports are enabled since
dmesg and setserial show the port.


root@phb:~# dmesg | grep -i tty
[ 0.000000] console [tty0] enabled
[ 1.072850] serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
[ 1.073628] 00:0a: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
root@phb:~# setserial -g /dev/ttyS*
/dev/ttyS0, UART: 16550A, Port: 0x03f8, IRQ: 4
/dev/ttyS1, UART: unknown, Port: 0x02f8, IRQ: 3
/dev/ttyS2, UART: unknown, Port: 0x03e8, IRQ: 4
/dev/ttyS3, UART: unknown, Port: 0x02e8, IRQ: 3
root@phb:~#

The computer has two serial ports, so I am a bit worried that only one
shows in the above. Maybe the other is disabled in BIOS. I'll check next
time I boot.


No breakout box or any such fancy stuff. The null modem cables I used
did work last time I used them, if find it unlikely all of them would
have broken when unused in the cupboard.


I tried both with and without RTS/CTS.

I added the user to group dialout, so the user can read and write to the
/dev/ttyS0 device.



Tapio Lehtonen


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Old 05-13-2011, 05:04 PM
Camaleón
 
Default How to use serial ports?

On Fri, 13 May 2011 16:04:30 +0300, Tapio Lehtonen wrote:

> I try to connect two pc hosts with serial ports with a null modem cable.
> I assumed starting kermit on both ends, setting line, speed etc. to
> suitable values would allow me to see what I type on the other end. But
> no such luck.

(...)

This may help:

Debian Linux: Set a Serial Console
http://www.cyberciti.biz/faq/howto-setup-serial-console-on-debian-linux/

Greetings,

--
Camaleón


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Old 05-13-2011, 05:15 PM
Chris Brennan
 
Default How to use serial ports?

On Fri, May 13, 2011 at 12:48 PM, Tapio Lehtonen <tapio.lehtonen@dnainternet.net> wrote:

Did not check BIOS for port settings, I supposed ports are enabled since dmesg and setserial show the port.





root@phb:~# dmesg | grep -i tty

[ * *0.000000] console [tty0] enabled

[ * *1.072850] serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A

[ * *1.073628] 00:0a: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A

root@phb:~# setserial -g /dev/ttyS*

/dev/ttyS0, UART: 16550A, Port: 0x03f8, IRQ: 4

/dev/ttyS1, UART: unknown, Port: 0x02f8, IRQ: 3

/dev/ttyS2, UART: unknown, Port: 0x03e8, IRQ: 4

/dev/ttyS3, UART: unknown, Port: 0x02e8, IRQ: 3

root@phb:~#



The computer has two serial ports, so I am a bit worried that only one shows in the above. Maybe the other is disabled in BIOS. I'll check next time I boot.



No breakout box or any such fancy stuff. The null modem cables I used did work last time I used them, if find it unlikely all of them would have broken when unused in the cupboard.



I tried both with and without RTS/CTS.



I added the user to group dialout, so the user can read and write to the /dev/ttyS0 device.




Tapio Lehtonen

Sorry if this is slightly OT, I've often wondered about using serial-console to access my 3 local headless servers here,*Camaleón link was very useful for the software side of it, what about the hardware side, not the com devices, but what type of*cabling is required? Just a F-F rs232/db9 cable?*



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> >>A: Because it reverses the logical flow of conversation.*> >>>Q: Why is top posting frowned upon?*
 
Old 05-13-2011, 05:57 PM
 
Default How to use serial ports?

Tapio,

From: Tapio Lehtonen <tapio.lehtonen@dnainternet.net>
Date: Fri, 13 May 2011 16:04:30 +0300
> I try to connect two pc hosts with serial ports with a null modem cable.

PPP over a null modem and through modems and telephone lines have worked
here for years. Configurations here.
http://carnot.yi.org/NetworksPage.html
mgetty provides ringback on the modem. Otherwise plain getty should work.

Recently the Dalton machine was replaced with different hardware and a
fresh installation of Squeeze. PPP has yet to work. Currently the null
modem is giving this in /var/log/syslog.

May 13 08:56:14 dalton kernel: [ 80.425375] PPP generic driver version 2.4.2
May 13 08:56:14 dalton pppd[2046]: The remote system is required to authenticate itself
May 13 08:56:14 dalton pppd[2046]: but I couldn't find any suitable secret (password) for it to use to do so.

Previously, PPP would refer to /etc/passwd but seems to have forgotten that.
A glitch between mgetty and pppd? Something new in authentication?

> ... starting kermit on both ends, ...

I've never used kermit in linux. In /etc/inittab on one machine you
could start getty. Then try a simple terminal emulator on the other machine.
If that fails check /var/log/syslog.

Regards, ... Peter E.



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Personal pages http://members.shaw.ca/peasthope/ .


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Old 05-14-2011, 08:27 AM
Tapio Lehtonen
 
Default How to use serial ports?

Chris Brennan kirjoitti:



Sorry if this is slightly OT, I've often wondered about using
serial-console to access my 3 local headless servers here, Camaleón
link was very useful for the software side of it, what about the
hardware side, not the com devices, but what type of cabling is
required? Just a F-F rs232/db9 cable?



Null-modem cable. If you have a serial cable that came with a modem for
example, that will not work.



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Old 05-14-2011, 03:51 PM
Tapio Lehtonen
 
Default How to use serial ports?

Chris Brennan kirjoitti:

On Fri, May 13, 2011 at 12:48 PM, Tapio Lehtonen <tapio.lehtonen@dnainternet.net <mailto:tapio.lehtonen@dnainternet.net>> wrote:

Did not check BIOS for port settings, I supposed ports are enabled
since dmesg and setserial show the port.

Now I did check BIOS settings. Only one serial port was enabled, I now
enabled both just for the heck of it. But I suspect the reason the one
port did not work was a PCI slot using the same interrupt. I changed the
interrupts and now both serial ports work, checked with kermit and
gtkterm. Also getty allows logging in from ttyS0.


So thanks for suggesting checking BIOS settings.


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Old 05-14-2011, 07:49 PM
Doug
 
Default How to use serial ports?

On 05/14/2011 11:51 AM, Tapio Lehtonen wrote:

Chris Brennan kirjoitti:
On Fri, May 13, 2011 at 12:48 PM, Tapio Lehtonen
<tapio.lehtonen@dnainternet.net
<mailto:tapio.lehtonen@dnainternet.net>> wrote:


Did not check BIOS for port settings, I supposed ports are enabled
since dmesg and setserial show the port.

Now I did check BIOS settings. Only one serial port was enabled, I now
enabled both just for the heck of it. But I suspect the reason the one
port did not work was a PCI slot using the same interrupt. I changed
the interrupts and now both serial ports work, checked with kermit and
gtkterm. Also getty allows logging in from ttyS0.


So thanks for suggesting checking BIOS settings.


How do you change interrupts? One of my pci slots shares an interrupt
with the on-board sound, so I avoid using it.

--doug

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