External Serial Modem on a 16450 UART

External Serial Modem on a 16450 UART

Post by Chris Matti » Mon, 06 Jan 1997 04:00:00



Does anyone know if it will matter if the serial port for an external
modem is a 16450 UART?  dmesg says that cua0 and cua1 are on a 16450
UART.

Our internet server is connected to a dedicated 28.8K line, but it has
REALLY bad performence.  In fact, when I dial into our ISP from home and
connect at 14.4K, I get better performance under Windoze than on the
server at work!


ttfn,

Chris

 
 
 

External Serial Modem on a 16450 UART

Post by Chris Harshma » Mon, 06 Jan 1997 04:00:00


Quote:> Does anyone know if it will matter if the serial port for an external
> modem is a 16450 UART?  dmesg says that cua0 and cua1 are on a 16450
> UART.

Absolutely.  The 8250, 16450, and 16550 chips weren't really suited to
handling anything above 9600.  You've only got a 1 byte buffer on that.
You can connect sucessfully at 19.2 if you're not running anything in
the background.  But as soon as Linux starts doing anything else
(accessing the hard drive, etc.) that one byte buffer fills and is
emptied before the OS can grab what's sitting there...  Resulting in
a mis-matched checksum and a resend of the data.  Performance will
drop to a crawl.

Quote:> Our internet server is connected to a dedicated 28.8K line, but it has
> REALLY bad performence.  In fact, when I dial into our ISP from home and
> connect at 14.4K, I get better performance under Windoze than on the
> server at work!

Replace the 16450 with a 16550A UART (note the 'A' at the end; most sold
nowadays are the revised chip).  Designed for today's faster speeds.

--
Chris Harshman--------------------------------------------------------------
XCC Systems Administrator, Johnston Computer Network, University of Redlands

    "Linux - the OS people choose without $200,000,000 in persuasion."

 
 
 

1. External v.34 modem & 16450 UART, OK?

I'm thinking of getting an external 28.8kbps modem but my serial port has
the 16450 UART instead of the 16550.  Is this a problem at this speed?  What
is the difference between the two UART?  So I just get an internal modem?

I'm sorry if this is FAQ.  Thank you very much for the help.

--
--------------
 Samuel C. Ramac
 Linux & Me.... Perfect together
---------------

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