lkml.org 
[lkml]   [2006]   [Aug]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: How to avoid serial port buffer overruns?
From
On Wed, Aug 16, 2006 at 12:45:59PM +0200, Raphael Hertzog wrote:
> While using Linux on low-end (semi-embedded) hardware (386 SX 40Mhz, 8Mb
> RAM), I discovered that Linux on that machine would suffer from serial
> port buffer overruns quite easily if I use a baudrate high enough (I start
> loosing bytes at >19200 bauds and I would like to make it reliable up to
> 115 kbauds). I check if overruns are happening with
> /proc/tty/driver/serial ("oe" field).
>
> Back when I was using the 2.4 kernel, I reduced dramatically the frequency
> of overruns by using the "low latency" and "preemptible kernel" patch [1]. But
> it still happened sometimes at 115 kbauds if the system was a bit loaded
> (with disk I/O for example).

In my experience, the way to avoid overruns on a serial port was to use
a buffered serial port UART (such as a 16550A for example). I remember
my 486 wasn't reliable about 19200 or 38400 (depending on how busy the
cpu was) when using an 8250. Using a 16550A based card and I could do
115200 without any issues since the UART had a 16 byte buffer to help
out the system. Unless your 386 has an add in card for the serial port,
it almost certainly has a very crappy UART and it would be very hard to
make it work reliably at higher speeds.

--
Len Sorensen
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2006-08-16 16:35    [W:0.067 / U:0.040 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site