"allisonp@world.std.com" "Allison J Parent" wrote:

><   You wrote:
><> And in fact the VS2K manual does make it clear that there are
><> interactions between the NCR and the disk controller (e.g. they share
><> buffers).
>
>This is never been adaquately explained.  I believe it to be a 
>misstatement or contextual error with regard to the VS2K manual.
>The 9224 UDC has it's own internally dedicated DMA logic that cannot 
>be used for any other device (LANCE is similar). That is indeed 
>curious as the 5380 does not have DMA (internally) at all so that it's 
>dependent on either PIO or some external DMA controller as it is not 
>possible to share a dma channel of either the LANCE or the UDC(9224). 
>If that is true how then would a memory buffer conflicting between the 
>disks and the SCSI device??  This is not a ka4xx thing as the raw chips 
>aka NCR5380, LANCE and UDC(9224) impose this structure on the system.

Maybe the manual is worng, but the DV and TV drivers have similar comments in 
them (and one or other of them has a whole list of gotchas-to-be-worked-around 
that implies that the driver author had access to more information from 
someoone).

Antonio

Antonio Carlini                            Mail: carlini@marvin.enet.dec.com
DECnet-Plus for OpenVMS Engineering
Digital Equipment Corporation              Worton Grange, Reading, England