Subject: Re: Oooooh... IDE to Q-bus/Unibus adapters.
To: None <>
From: Allison J Parent <>
List: port-vax
Date: 07/07/1999 23:15:43
<...but also remember that you're looking at PCI IDE chips!  I don't know

Why would I look at them?  they are awkward to use on a 16bit bus and the
IDE interface for PIO requires very little.  Qbus DMA is pretty simple
if you limit it to single transacion and no list linkages.

I didn't bring PCI and their chips into this discussion.  Look at the 
Ukraine design for how simple it can be with PIO alone.

<products which use a "standard" IDE interface but which also support
<DMA ... they supply the DMA engine that merely does the PIO to the chip
<for you).

Contradiction of terms.  PIO is cpu doing the work, the 8237 pcstyle DMA
is not a cpu but a simple get/put DMA.

<Also, AFAIK, every VAXstation that has a SCSI chip has the capability
<of doing DMA to/from that SCSI chip.  It is merely an issue of the NetBSD
<driver for that SCSI chip not supporting DMA.

Yep!.  Reason, apparently a lack of documentation on the DMA system
and it's interactions with the brain hampers NCR chip.