[clug-talk] serial console help

Gustin Johnson gustin at echostar.ca
Mon Sep 26 09:16:28 PDT 2005

Quoting lewkor at telus.net:

> Quoting Gustin Johnson <gustin at echostar.ca>:
>> I am running a qemu session with -nographic which means that there is no
>> graphic output.  Control of the VM occurs across a virtual serial connection
>> (/dev/ttyS0 to the guest, and either stdio or a pty on the host).  The
>> problem is when I run vim somefile I get some garbled characters and the
>> following sprayed across much of the screen:
>> serial8250: too much work for irq4
>> I have not had much experience with serial consoles (except as a user of the
>> UofC's DevlNET, which I kinda miss), so any help would be appreciated.
>> The output of setserial:
>> setserial -g /dev/ttyS*
>> /dev/ttyS0, UART: 16450, Port: 0x03f8, IRQ: 4
>> I have also played with various rate (aka speed) settings from 9600 to
>> 115200
> You may have to go down even lower baud rates to get this working.  
> As you can
> see qemu thinks the chip is a 16450.  That chip had no fifo, so on receiving

Actually qemu is emulating a 16450, which makes sense because there would less
overhead in emulating a UART without a buffer.

> the data has to come slow enough that the CPU can get the data out of the
> buffer before the next byte otherwise the chip will raise an overrun flag
> indicating it could not keep up to the data stream.  The first thing that I'd
> try is 2400 baud (see comment below).

2400 was no more successfull than the other baud rates I tried.  I will 
try some
of the lower rates later today.

Ah the memories this brings... I had a 386 laptop with this UART, could 
only run
my new 28.8 USR @ 19,200 until I upgraded my machine.

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