> AFAIK, you cannot do DMA to virtual addresses in general. The only
> options I'm aware of that did it are the DR-780, it's cousin the BI
> version (IIRC, the DMB32), and the third-pary VAXBI quad IEEE-488
> adapter for which I wrote the firmware (a Z-80 looking things=20
> up in the
> VAX page tables. Yum!). All DMA is to physical addresses.

Not relevant to the current discussion, but just to put
the record straight for anyone reading this in the future,
the DMB32 is the VAXBI version of the DMF32 (it does asynch
and synch and parallel I/O). It has more addressing modes
than you can shake a stick at (four) and it can indeed read
VAX page tables (at least until the XVA/XPA project changed
the format).

It's based on the 68000 - so that's two 16 bitters that can
do something with VAX page tables.

FWIW: the VAXBI analogue to the DR780 would probably be
a DRB32. I think it existed, but I know nothing about it.


Antonio

--=20

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Antonio Carlini arcarlini@iee.org