Re: What to do with slow Chip/ST RAM

[Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>]

abs%NetBSD.org@localhost wrote:

>       Both amiga and atari have the concept of 'fast' and 'slow' RAM.
>       For a system with a reasonable amount of fast RAM using the
>       slow RAM can actually slow things down, though it seems like
>       a shame to waste it...

I guess ST is on 16 bit bus and TT is on 32 bit bus on atari,
and both could be handled by pmap/uvm with proper priorities
by MI uvm(9) API. IIRC, mvme68k has some code which handles
slower (no cache) VME bus memory.

>       Jared has written a driver for the sgimips O2 to allow it to
>       access some of its extra memory banks as a block device, which
>       means it can use it as a RAM swap device. (The issue with the O2
>       is different, as the current NetBSD kernel cannot use that extra
>       memory directly, but the principle is related).

Our mips pmap can't handle physical memory located at
PA higher than 256MB, so his driver just provides alternative
usage of memories which can't be handled by uvm/pmap,
as >4GB PAE memory on i386.

On the other hand, x68k has the similar RAM disk device (bmd)
for optional memory on the Nereid board.
---
Izumi Tsutsui