Subject: Re: ie0: DMA underrun
To: Jason Thorpe <thorpej@SJ.Xenotropic.COM>
From: David Jones <dej@achilles.net>
List: port-sparc
Date: 11/19/1995 08:36:49
> ie0: DMA underrun
> 
> Lots of 'em.  It doesn't seem to have trashed anything, that is after the 
> new libc.so.12.3 was installed things kept working.  But, they are 
> somewhat annoying, and could potentially lead to some trashed data, I'm 
> sure.
> 
> Worth noting, I did get this message before when using the old "si" 
> driver, but they're happening with much greater frequency.

I got this too while I was developing the DMA si driver.  I think the worst
consequence is runt packets, which _should_ be detected and dropped by the
receiver.

The Sun-3 architecture manual says that Ethernet DMA has higher priority
than SCSI DMA.  This makes sense - Ethernet is time-sensitive (sustain
1.25 MB/s or you lose) and SCSI is not, unless you are mastering CD-ROMS
using a CDR drive.  But it doesn't look like that from what you observe.

Funny thing - I don't get DMA underruns running Gordon's latest incarnation
of the si driver.  It might be worse if X is running, I dunno.

What I find really disturbing is that you get underruns even without
SCSI DMA.  Is the Ethernet on-board, or is it a separate VME card?