[SeaBIOS] [PATCH] Report on f-segment UMB ram also.

Kevin O'Connor kevin at koconnor.net
Thu Feb 21 05:40:41 CET 2013


On Tue, Feb 19, 2013 at 09:16:30AM +0000, David Woodhouse wrote:
> On Mon, 2013-02-18 at 10:34 -0500, Kevin O'Connor wrote:
> > Some old DOS programs can also use f-segment space as Upper Memory
> > Blocks (UMB), so also report on what space is available in debug
> > messages.
> 
> Should we mark it as available in E820 too?

The f-segment is typically made read-only, so it's not memory an OS
can really use.  (As I understand it, the old DOS programs that use
UMB could detect empty space in the f-segment and use the 386 paging
system to map high-memory in its place.)

In any case, my experience has been that the first 1 megabyte of the
e820 is "magic": 0-0x9fc00 = RAM, 0x9fc00=0xa0000 = RESERVED,
0xa0000-0xf0000 = hole, 0xf0000-0x100000 = RESERVED.  It's possible to
tweak the ranges a little (eg, 0xe0000-0x100000 = RESERVED), but
fundamental changes (even if more correct) have a good chance of
breaking programs.

-Kevin



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