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From: julian@tfs.com (Julian Elischer)
Subject: Re: [386BSD] more than 16MB?
Message-ID: <1993Jan6.203341.6812@tfs.com>
Organization: TRW Financial Systems
References: <C0EHx0.qr@space.physics.uiowa.edu> <1if0p8INNfau@Germany.EU.net>
Date: Wed, 6 Jan 1993 20:33:41 GMT
Lines: 51
In article <1if0p8INNfau@Germany.EU.net> bs@Germany.EU.net (Bernard Steiner) writes:
>In article <C0EHx0.qr@space.physics.uiowa.edu>, ljg@space.physics.uiowa.edu (Larry Granroth) writes:
>> Is anyone out there running 386bsd on an ISA-bus machine with more than
>> 16MB ram?
>
>Yes. I've seen a machine with 20MB and heard of one with 64 MB
>(yes, sixty-four) No, not me...
I doubt this very much
The problem is that for reasons not obvious (but real) the kernel
is compiled for FE000000. This is 32MB below the top
of the address space. The kernel for 0.1 requires that it map
the entire physical address space above this address, PLUS some other
areas that are mapped in a non 1:1 manner (e.g. raw-IO address translation
buffers)
the upshot of this is that 386BSD can only make use of (32 - X)MB of real
ram (where X is an unknown number) 20MB certainly works.
0.2 solves this shortcoming by some rather ingenious means.
>
>> Does 386bsd support this?
>
>Looks like it.
20 works, 24 may work.. after that I doubt it.
(bill has some special compiles for >> 32MB but they require several
patches and 0.2 should solve the problem properly)
>
>> Does it (does it need to?) support
>> DMA above 16MB?
>
>No idea. I'd be interested in the answer, though.
for floppy, the dma is supplimented by a bounce buffer.
for SCSI it is not.
however the EISA scsi drivers do support 32 bit adresses. so bounce buffers
are not needed.
>
>-Bernard
julian
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