From: jlaiho@ichaos.nullnet.fi (Juha Laiho) Subject: About DMA xfers to >16MB memory Date: Tue, 6 Jul 1993 10:24:19 GMT
bsa@kf8nh.wariat.org (Brandon S. Allbery) said:
<<Some talk about memory speeds removed..>>
>Probably because Linux in > 16MB will preferentially put the buffers < 16MB
>and programs above it, so it can do DMA to/from the buffers. The 16MB magic
>number is due to ISA's inability to support DMA beyond 16MB.
>
Mostly true, but some manufacturers (at least Intel) seem to have special
arrangements to handle DMA transfers to above 16MB region as well.
If someone wants to do the code, I can dig out an Intel 303 handbook, that
contains (I think) all the necessary information.
(Intel 303 is an ISA-bus 386/33 with 64k cache; quite old, full-sized board)