Very Computer

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

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).
--

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

Very Computer

Losing serial port characters during backup

Losing serial port characters during backup

Losing serial port characters during backup

Losing serial port characters during backup