Adding serial ports 3 and 4

Adding serial ports 3 and 4

Post by Cameron Hutchiso » Thu, 05 Feb 1998 04:00:00



I have found that my two serial ports are not enough and would like to add
two more. So I went out and purchased a 2-port board with a 16650 and
plugged it into my machine. I've got some questions regarding the board
configuration.

Here's how I plan to use the serial ports:
ttya - mouse
ttyb - 33.6K modem - net connection
ttyc - Running pppd, so I can connect to my box with TCP/IP; nothing
        permanently connected.
ttyd - Raw serial for anything that needs it. Nothing permanently
        connected.

It appears that I can configure ttya and ttyc to share the same IRQ (IRQ4),
ditto for ttyb and ttyd (IRQ3). What problems can this cause by having two
serial ports using the same IRQ? I have the ability to configure the card
to use other IRQs (probably 9 and 12). Should I do this? If so, do I need
to manually reconfigure the kernel? I configured the board for IRQ 9 and 12
but it seems that the kernel cannot auto-detect this, as it came up saying
that ttyc had IRQ4 and ttyd had IRQ3.

The kernel recognised the presence of the extra serial ports but reported
them as 16550A, not 16650. Is this going to be a problem in practice?

Is there any online documentation that describes how this interrupt sharing
works?

--


 
 
 

Adding serial ports 3 and 4

Post by Jeff Kloud » Thu, 05 Feb 1998 04:00:00


Cameron,

Just went through something simular.  You can use "setserial" (see the
man pages for how) to change the IRQs and other settings.  This will
help you in getting the right settings.  Then you will need to edit
/etc/rc.d/rc.serial and comment out the automatic settings line and
uncomment out the manual settings line, of course editted to your
setting needs.  Then you have to edit /etc/rc.d/rc.local adding the line
/etc/rc.d/rc.serial.  This was a little puzzling to me because I thought
everything in rc.d would run at boot up, but that doesn't seem to be the
case.

Anyway, hope this helps.

Jeff


> I have found that my two serial ports are not enough and would like to add
> two more. So I went out and purchased a 2-port board with a 16650 and
> plugged it into my machine. I've got some questions regarding the board
> configuration.

> Here's how I plan to use the serial ports:
> ttya - mouse
> ttyb - 33.6K modem - net connection
> ttyc - Running pppd, so I can connect to my box with TCP/IP; nothing
>         permanently connected.
> ttyd - Raw serial for anything that needs it. Nothing permanently
>         connected.

> It appears that I can configure ttya and ttyc to share the same IRQ (IRQ4),
> ditto for ttyb and ttyd (IRQ3). What problems can this cause by having two
> serial ports using the same IRQ? I have the ability to configure the card
> to use other IRQs (probably 9 and 12). Should I do this? If so, do I need
> to manually reconfigure the kernel? I configured the board for IRQ 9 and 12
> but it seems that the kernel cannot auto-detect this, as it came up saying
> that ttyc had IRQ4 and ttyd had IRQ3.

> The kernel recognised the presence of the extra serial ports but reported
> them as 16550A, not 16650. Is this going to be a problem in practice?

> Is there any online documentation that describes how this interrupt sharing
> works?

> --



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fax:  (972) 234-3600


 
 
 

Adding serial ports 3 and 4

Post by John Smit » Thu, 05 Feb 1998 04:00:00



>I have found that my two serial ports are not enough and would like to add
>two more. So I went out and purchased a 2-port board with a 16650 and
>plugged it into my machine. I've got some questions regarding the board
>configuration.

>Here's how I plan to use the serial ports:
>ttya - mouse
>ttyb - 33.6K modem - net connection
>ttyc - Running pppd, so I can connect to my box with TCP/IP; nothing
> permanently connected.
>ttyd - Raw serial for anything that needs it. Nothing permanently
> connected.

doable must but each serial port will need full use of an IRQ when in use.
So to use all of these ports concurrently you will need to give each port
its own irq line

Quote:

>It appears that I can configure ttya and ttyc to share the same IRQ (IRQ4),
>ditto for ttyb and ttyd (IRQ3). What problems can this cause by having two
>serial ports using the same IRQ?

Hanging and very, very slow transmissions

Quote:> I have the ability to configure the card
>to use other IRQs (probably 9 and 12). Should I do this? If so, do I need
>to manually reconfigure the kernel? I configured the board for IRQ 9 and 12
>but it seems that the kernel cannot auto-detect this, as it came up saying
>that ttyc had IRQ4 and ttyd had IRQ3.

Actually it can if you slightly tweak the source code a bit.  However if you
are a non-coder,  this is not necesary as you can use the setserial command
to tell the serial driver what irq to use for a particular port include
telling it to auto detect it.  Until you run setserial on the needed ports
the driver will assume the default settings of irq 4 and 3.  Be carefull
with irq 12 as this will be the irq of you mouse if you use or plan  to use
a PS/2 one.  And make sure you tell your bios that whatever other irq's you
use for your ports are in use (if you are using a pci system)

Quote:

>The kernel recognised the presence of the extra serial ports but reported
>them as 16550A, not 16650. Is this going to be a problem in practice?

No problem unless they are 16650's, if there are such serial ports

Quote:>Is there any online documentation that describes how this interrupt sharing
>works?

You cannot share serial irq's similtainiously.

>--



 
 
 

Adding serial ports 3 and 4

Post by M. Buchenried » Sat, 07 Feb 1998 04:00:00



>I have found that my two serial ports are not enough and would like to add
>two more. So I went out and purchased a 2-port board with a 16650 and
>plugged it into my machine. I've got some questions regarding the board
>configuration.

[...]

This is a standard serial I/O-card, I presume.

Quote:>It appears that I can configure ttya and ttyc to share the same IRQ (IRQ4),
>ditto for ttyb and ttyd (IRQ3).

This is indeed the default setup on an IBM-comp. PC .

Quote:>What problems can this cause by having two
>serial ports using the same IRQ?

It does not work, unless you're using specific hardware that supports
IRQ sharing on the ISA bus. A standard I/O card doesn't. You'll need
a multiserial card to be able to share an IRQ between several devices.

Quote:>I have the ability to configure the card
>to use other IRQs (probably 9 and 12). Should I do this?

If you want to be able to use 4 serial ports, yes.

Quote:>If so, do I need
>to manually reconfigure the kernel? I configured the board for IRQ 9 and 12
>but it seems that the kernel cannot auto-detect this, as it came up saying
>that ttyc had IRQ4 and ttyd had IRQ3.

See "man setserial" . The "setserial" command is telling Linux about
this kind of setup.

Quote:>The kernel recognised the presence of the extra serial ports but reported
>them as 16550A, not 16650. Is this going to be a problem in practice?
>Is there any online documentation that describes how this interrupt sharing
>works?

Read the Serial-HOWTO . It will tell you why it does not work.

Michael
--

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