[comp.unix.sysv386] memory mapping

davidsen@sixhub.UUCP (Wm E. Davidsen Jr) (12/26/90)

  Let me ask a question here, based on something I partially remember
from setting up ISC some months ago... There was a table which defined
memory, and we used it to define memory which could not do DMA, to force
the o/s to fake it. I *thought* I read in the description of that table
that it could also be used to block out a section of RAM to keep the o/s
from using it, but to still use RAM *above* the reserved space.

  The docs are miles away, and I'm on vacation to boot. If someone can
come up with the details they may be germane to this discussion. I
thought the purpose of that capability was to allow blocks of reserved
memory for memory mapped i/o such as ethernet cards, etc.

  Note: we got this from Dell, some of it said ISC and some Dell. We
found certain other things about the implementation which didn't fit our
needs, so Ionly worked with it for a few weeks.
-- 
bill davidsen - davidsen@sixhub.uucp (uunet!crdgw1!sixhub!davidsen)
    sysop *IX BBS and Public Access UNIX
    moderator of comp.binaries.ibm.pc and 80386 mailing list
"Stupidity, like virtue, is its own reward" -me

marc@dumbcat.sf.ca.us (Marco S Hyman) (12/28/90)

In article <2732@sixhub.UUCP> davidsen@sixhub.UUCP (bill davidsen) writes:
    
      Let me ask a question here, based on something I partially remember
    from setting up ISC some months ago... There was a table which defined
    memory, and we used it to define memory which could not do DMA, to force
    the o/s to fake it. I *thought* I read in the description of that table
    that it could also be used to block out a section of RAM to keep the o/s
    from using it, but to still use RAM *above* the reserved space.

There is a MEMRANGE entry in /etc/default boot.  Mine looks like (386/ix
2.0.2)

	MEMRANGE=0-640K:0,1M-15M:0,16M-15M:1

Note that the last entry (16M-15M:1) is in reverse order.  This tells the OS
to scan from the top down when looking for memory in this range.  The :1
says DON'T use DMA for this range.

I forget where it's documented, maybe someone else can say where in TFM to
look.

// marc
-- 
// marc@dumbcat.sf.ca.us
// {ames,decwrl,sun}!pacbell!dumbcat!marc