56k modem in 486

56k modem in 486

Post by Tina and Dea » Thu, 23 Sep 1999 04:00:00



Good morning,

    i have recently put together a firewall just for testing.
Everything works fine with my 14.4 modem in it but when i took the 56k
modem out of one of my other linux boxes and put it in the firewall box
it started failing.  i can connect to the internet and get a proper ip
address, but i loose about 2/3 of the data.  dns is sort of working and
so does surfing but only if i leave them for an unacceptable amount of
time.  i have tried to mimic the configuration from the linux box where
the 56k modem works perfectly and cannot see anything that i missed.
Both of these are ISA modems based on rockwell chipsets.

    Is it possible that the 486 mainboard simply cannot handle the
modem?
    What configurations should i check other that my setserial command
(which is identical)?

thanks,
dean

 
 
 

56k modem in 486

Post by Michael Kel » Thu, 23 Sep 1999 04:00:00




Quote:>   Is it possible that the 486 mainboard simply cannot handle the
>modem?

If it has a buffering UART I'd think it unlikely.  I had an external
USR modem running off serial port with 32 byte buffer uarts
(and the 16 byte buffered ones should work nearly as well)
and had no problem.

You might check further into setserial.  I think there's a setting
when you configure the port to tell it that the uart has hw buffers
and to use fifo buffering.
Also there's a utility to set the hw priorities in Linux.  I'm not in
Linux right now to check the name but if you search the web
for something that manipulates the PIC interrupt controller
chip to set priorities you should find it.  The main reasont the
author developed it was to optimize modem downloads.
It may help and it's a freeware.

Mike

--

"Genius gives birth, talent delivers."

           -- Jack Kerouac

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56k modem in 486

Post by John Thompso » Thu, 23 Sep 1999 04:00:00



> Good morning,

>     i have recently put together a firewall just for testing.
> Everything works fine with my 14.4 modem in it but when i took the 56k
> modem out of one of my other linux boxes and put it in the firewall box
> it started failing.  i can connect to the internet and get a proper ip
> address, but i loose about 2/3 of the data.  dns is sort of working and
> so does surfing but only if i leave them for an unacceptable amount of
> time.  i have tried to mimic the configuration from the linux box where
> the 56k modem works perfectly and cannot see anything that i missed.
> Both of these are ISA modems based on rockwell chipsets.

>     Is it possible that the 486 mainboard simply cannot handle the
> modem?
>     What configurations should i check other that my setserial command
> (which is identical)?

Even an XT-class machine should be able to handle the
throughput on a 56k modem. Make sure you're using the same
init string for the modem.  Make sure the uart is buffered
and enabled.  Make sure the computer-to-modem speed is
appropriate.

--


 
 
 

56k modem in 486

Post by Larry Jansc » Fri, 24 Sep 1999 04:00:00



> >   Is it possible that the 486 mainboard simply cannot handle the
> >modem?

> If it has a buffering UART I'd think it unlikely.  I had an external
> USR modem running off serial port with 32 byte buffer uarts
> (and the 16 byte buffered ones should work nearly as well)
> and had no problem.

> You might check further into setserial...

Beg to differ. In many older machines, the port's UART is an 8550,
limited to 19.2K, going downhill, and that's with a stiff tailwind. :-D

Either replace the serial card with a 16550-driven serial card or
disable the built-in serial port and install a 16550-driven port,
depending on the particulars. Dig deep - this might set you back as much
as US$20!

-Larry
--
Larry Jansch

The next century/millennium starts in 2001, not 2000.
There was no year "0", so the first century ran from
the year 1 to the year 100. The second century ran
from the year 101 to the year 200. And so on.

  ljansch.vcf
< 1K Download
 
 
 

56k modem in 486

Post by David » Fri, 24 Sep 1999 04:00:00



> Beg to differ. In many older machines, the port's UART is an 8550,
> limited to 19.2K, going downhill, and that's with a stiff
> tailwind. :-D

The original poster said this was an ISA internal modem.  Not an
external.  So this isn't a concern.  Whatever UART (or UART emulation)
that is used is built-into the card.

My guess would be that there's an interrupt conflict.  If the internal
modem is grabbing a port or an interrupt that a physical serial port is
also using, it will cause erratic behavior.

-- David

 
 
 

56k modem in 486

Post by G. Smi » Fri, 24 Sep 1999 04:00:00


Check out the setserial command.  I used it to set my irq to what it
really was (5).  It was set to 4, and I thought Linux thought I had a
300bps modem.

setserial /dev/??? irq ?

Hope this helps.
Gary Smith

Quote:>The original poster said this was an ISA internal modem.  Not an
>external.  So this isn't a concern.  Whatever UART (or UART emulation)
>that is used is built-into the card.
>My guess would be that there's an interrupt conflict.  If the internal
>modem is grabbing a port or an interrupt that a physical serial port is
>also using, it will cause erratic behavior.
>-- David

 
 
 

56k modem in 486

Post by Tina and Dea » Sat, 25 Sep 1999 04:00:00


Good morning guys,

    Thanks for all of the input.  So how do i find where the bottleneck
is.  It seems as though (correct me if i get this wrong) the modem is
capable of the full 56k and is likely pulling that all down, but something
locally is funneling that info to 19200.  It's like it takes the 19200
that the system can handle and the rest is discarded.  Does that explain
why when i ping internet addresses i get a packet loss that is about 67%
each time?  i have checked and double checked for conflicts but can't find
any.  Both modems are set to the same irq anyway, so i would expect
similar instability from the 144k (wouldn't i?)  Here is the result of
"setserial -a /dev/ttyS3"

/dev/ttyS3, Line 3, UART: 16450, Port: 0x02e8, IRQ: 3
        Baud_base: 115200, close_delay: 50, divisor: 0
        closing_wait: 3000, closing_wait2: infinte
        Flags: spd_normal session_lockout

thanks again to all who responded,
dean
--------------------------------


> Good morning,

>     i have recently put together a firewall just for testing.
> Everything works fine with my 14.4 modem in it but when i took the 56k
> modem out of one of my other linux boxes and put it in the firewall box
> it started failing.  i can connect to the internet and get a proper ip
> address, but i loose about 2/3 of the data.  dns is sort of working and
> so does surfing but only if i leave them for an unacceptable amount of
> time.  i have tried to mimic the configuration from the linux box where
> the 56k modem works perfectly and cannot see anything that i missed.
> Both of these are ISA modems based on rockwell chipsets.

>     Is it possible that the 486 mainboard simply cannot handle the
> modem?
>     What configurations should i check other that my setserial command
> (which is identical)?

> thanks,
> dean

 
 
 

56k modem in 486

Post by Michael Kel » Sat, 25 Sep 1999 04:00:00




Quote:>/dev/ttyS3, Line 3, UART: 16450, Port: 0x02e8, IRQ: 3

------------------------------------|||||||||||||

This is bad!  16450 has no hw buffers!  You need to spring for either
a serial port card or an internal modem that has 16550 or better UART.

Depends how much $$$ you have to blow.  I shelled out $70 for
a serial card with 2 16550C UARTs with 32 byte hw buffers in
each direction w/2 serial ports.  Without hw buffering your
performance is going to be shaky.  Also the utility I was talking
about for setting your irq priorities is called IRQTUNE.

There's a chance you just haven't set the port correctly and Linux
is seeing a 16550 UART as 16450.  It won't use the HW buffers
on the UART unless you explicity tell it that it's a 16550 UART
on the port(at least it won't in Slackware) so read up more on
setserial command options(or it could be in the port device creation
commands I don't remember).  If that doesn't do it then it looks like
you'll need the newer hw.

Good luck.

Mike

--

"Genius gives birth, talent delivers."

           -- Jack Kerouac

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56k modem in 486

Post by Tina and Dea » Sun, 26 Sep 1999 04:00:00


Good morning,

    Ya, but this modem works perfectly in my pentium board with what seem
to be identical settings and 'setserial -a' results are identical (with
the exception of a session_lockout on the 486).

on both machines my setserial command is:
setserial /dev/ttyS3 uart 16450 port 0x2E8 irq 3

thanks,
dean
_________________________




> >/dev/ttyS3, Line 3, UART: 16450, Port: 0x02e8, IRQ: 3
> ------------------------------------|||||||||||||

> This is bad!  16450 has no hw buffers!  You need to spring for either
> a serial port card or an internal modem that has 16550 or better UART.

 
 
 

56k modem in 486

Post by Michael Kel » Mon, 27 Sep 1999 04:00:00




Quote:>Good morning,

>    Ya, but this modem works perfectly in my pentium board with what seem
>to be identical settings and 'setserial -a' results are identical (with
>the exception of a session_lockout on the 486).

Hmmmm, If I was trying to use a communication device in a machine
with a CPU that's 20 x slower or more than the current one I might
want to go with some hardware buffering.

Could be another cause but slow CPU allowing dropped bytes left
and right would be my first guess. :)

Who knows?  I've been wrong before... will be again. :)

Mike

--

"Genius gives birth, talent delivers."

           -- Jack Kerouac

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56k modem in 486

Post by Brent R Bria » Mon, 27 Sep 1999 04:00:00


If you are dropping characters try setting the high-water-mark on the buffer to 12
or 14.  That will cause the IRQ to be generated while there are still 2 characters
(or more) left in the buffer.  If you wait for the buffer to completely fill, you
may drop characters on the slower processors.

B





> >>Good morning,

> >>    Ya, but this modem works perfectly in my pentium board with what seem
> >>to be identical settings and 'setserial -a' results are identical (with
> >>the exception of a session_lockout on the 486).

> >Hmmmm, If I was trying to use a communication device in a machine
> >with a CPU that's 20 x slower or more than the current one I might
> >want to go with some hardware buffering.

> >Could be another cause but slow CPU allowing dropped bytes left
> >and right would be my first guess. :)

> I agree....get hardware buffering.   I'm using 115200 baud on 3 serial ports
> with a 386sx with no problems using 16550 chips. (not Linux however -
> DOS/DesqView)

> --
> Cheers,

> The future was never like this!

 
 
 

56k modem in 486

Post by Tina and Dea » Tue, 28 Sep 1999 04:00:00


Good morning,

    Ok, i finally get it!  The fact that the modem worked in the pentium with
'setserial uart 16450' was throwing me off.  i double-checked my modem docs
and reread the setserial man page and found that the modem actually has a
16550 uart and setserial must be set to uart 16550A to enable FIFO.  This is
done now and i am happily surfing with my 56k modem in my 486.

    Thanks for all of your patience, especially Michael Kelly.

regards,
dean

__________________________




> >Good morning,

> >    Ya, but this modem works perfectly in my pentium board with what seem
> >to be identical settings and 'setserial -a' results are identical (with
> >the exception of a session_lockout on the 486).

> Hmmmm, If I was trying to use a communication device in a machine
> with a CPU that's 20 x slower or more than the current one I might
> want to go with some hardware buffering.

> Could be another cause but slow CPU allowing dropped bytes left
> and right would be my first guess. :)

> Who knows?  I've been wrong before... will be again. :)

> Mike

> --

> "Genius gives birth, talent delivers."

>            -- Jack Kerouac

> (Remove NOSPAM, if present, to reply via email)

 
 
 

1. Old 486 and 56k modem

I have an old 486 25sx with 16450 serial and ethernet.
I would like to use it as a gateway to my home computers, but I remember
that 16450 serials are not enough for a 56k modem.

Is it true?
New kernels have a solution?

Thanks in advance for any reply.
--
--
Mario Giammarco
mgiammarco$libero,it

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