Losing serial port characters during backup

Losing serial port characters during backup

Post by Clifton Ko » Wed, 01 Oct 1997 04:00:00



  I just installed a 4mm DAT backup on my machine and appear to be losing
characters from the serial port while a backup is in progress.  I'm backing
up a 3 gig IDE hard drive onto a SCSI 4mm tape drive on a dual Pentium Pro 180
system.  The hard drive is connected to the on-board IDE controller of a
SuperMicro p6DNF motherboard (I think that's the number) and the DAT controller
to an Adaptec 1542 SCSI controller.  While I was doing the backup, I was
running a SLIP link into work and seemed to be losing some character
occasionally.

  Any idea what's going on?  I've heard of interrupt latency problems with
serial ports and IDE drives in the past, but the serial port uses 16550 UARTs
and I'd think the PPros would be quick enough to be able to service the IDE
drives and serial ports.  Any settings I could change within Linux to help
the matter out?

Thanks,
Cliff
--
-----------------------------------------------------------------------------
    Cliff Koch
    Motorola Cellular Infrastructure Division

 
 
 

Losing serial port characters during backup

Post by Peter Knoppe » Thu, 02 Oct 1997 04:00:00



>  I just installed a 4mm DAT backup on my machine and appear to be losing
>characters from the serial port while a backup is in progress.  I'm backing

...

Use hdparm to toggle the unmaskirq flag. Some older IDE disks
behave erroneously when a data-transfer is interrupted for a
short while (for instance to service a serial port). The default
behaviour for the linux IDE driver is to disable interrupts
when a disk operation is in progress. Modern IDE disks will work
reliably with interrupts enabled while a disk operation is in
progress. Of course, there is no guarantee that your disk drive
is compliant... However disk > 1G generally are.

Hdparm lives in /sbin (at least on my RedHat linux system).
--


 
 
 

Losing serial port characters during backup

Post by M. J » Thu, 02 Oct 1997 04:00:00




>  Any idea what's going on?  I've heard of interrupt latency problems with
>serial ports and IDE drives in the past, but the serial port uses 16550 UARTs
>and I'd think the PPros would be quick enough to be able to service the IDE
>drives and serial ports.  Any settings I could change within Linux to help
>the matter out?

(I'm using Redhat 4.2)

I had to disable interrupt masking so that IDE disk access wouldn't cause
character losses while downloading.   Now, everythign works great!

I entered this into my /etc/rc.d/rc.local startup script:

hdparm -u /dev/hda

Mark

 
 
 

1. Lost characters from serial port (kernel bug ?)

Hi there !

First of all I would like to thank you very much for the
superb linux system.

However, there are some small problems which I can`t solve...

When I am running X, the serial port is loosing characters. ( >= 9600 baud)
This happens as soon as the window is scrolling (only then).
I hooked up my oscilloscope to the IRQ-line. Every time a character
is lost it looks like the Xserver is disabling interrupt for 10 ms.
I recompiled the kernel for having the serial interrupts at every character,
not just after 13 characters in the buffer or so. It helped a little.
(very little).

I suspect that something is wrong with the interrupt-priorities
in the linux kernel. How is the interrupt-controller chips set up ?
Do linux use rotating priorities ?
Can the problem have anything to do with timer0 which has the highest priority.
Or are things set up in some other way on these chips ???

I am using a Pentium 60 Mhz, Intel motherboard, 16 M ram,
Conner cfp1060 disk (the one with the bug). buslogic 445.
S3 928 pci-graphics. Serial chips 16550A, I tried the ones on my
motherboard and through a isa-bus slot on the modem.

I have a friend with a 485 dx 50 , 4Mram , Tseng W32
where things are working perfectly.
I also had this problem (I think, I'm not 100 % sure I have tested it)
 on my old computer (cyrix 33mhz 486, with 4 Mram, Video7 graphics).

I used Linux kernel 1.1.8 slackware.
I have tried kernel 1.1.75 with similar results.
I have tried both X-version 2.1 and 2.1.1 and 3.0

I fetched the source for X11R6, I have searched for some CLI-instructions,
but I havn't found too many...

Another thing...

      I am writing a program which uses memory mapped files.
      It only works for reading, when the memory contents is updated,
      it is not wrtten to disk after a close...
      I have not yet checked with latest kernel and tools.
      Is it supported yet ???

             Have a nice time...
                Linux hacker MtM

                    in real life: Magnus Persson

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