Kevin O'Connor wrote: 
On Tue, Apr 13, 2010 at 02:26:10PM +0800, Roy Tam wrote:
  
2010/4/12 Gerhard Wiesinger <lists@wiesinger.com>:
    
3.) There is also a problem with the reported base memory under QEMM386
(HIMEM.SYS and EMM386.EXE is correct here). It is 646kB instead of 640kB.
Therefore base memory test fails. I guess that reporting memory CMOS
tables/interrupt functions are not implemented correctly.
      
- The Base Memory > 640K error seems to be SeaBIOS related. QEMU Bochs
BIOS(tested with both -old-bios hack in 0.12 series and old 0.11.1)
will just freeze after QEMU counted RAM.(Tested with ScriptPC and
Bochs).
    

The SeaBIOS log would really help.  This can be done by adding:

-chardev stdio,id=seabios -device isa-debugcon,iobase=0x402,chardev=seabios

to the qemu command line.

The memory can be obtained in several places (int 12, int 1588, int
15e801, int 15e820, and mem 40:13).  All look fine to me from looking
at the code.

OK, I made some research on the topic. Problem is that QEMM pushes the Extended BIOS data area to High RAM on some machines (QEMU, P733). Therefore 640k low memory is available and checkit reports 640kB + 6kB=646kB EBIOS DATA AREA. Whats strange that on a physical Pentium 733 machine this works correctly (details see below and attached files), maybe someone can try to find the problem with QEMM+Checkit 3.0 (maybe there is still some other BIOS function incorrectly implemented). QEMM parameter NOXBDA avoids moving the XBDA up to HI RAM and therefore checkit reports 640kB well.

SeaBIOS seems to be correct (see below and attached patch files and description below).
Total Memory: 256MB (262144kB), Base RAM: 637kB
Extended BIOS Data Area size: 3 kB, segment=9f40

SCSI option ROM:
After option ROMS, Total Memory: 256MB (262144kB), Base RAM: 634kB
Extended BIOS Data Area size: 6 kB, segment=9e80

MS-DOS 6.22, QEMM 8.03

QEMU

Testcase

BDA

40h:13h

INT

12h

INT 15h,

AX=E820h

EBIOS

DATAAREA

Checkit

3.0

Plain DOS, after Boot

634kB

634kB

634kB

9E80h-A000h (6k)

640kB

HIMEM.SYS+EMM386.EXE

634kB

634kB

634kB

9E80h-A000h (6k)

640kB

QEMM

640kB

640kB

634kB

CEB5h-D035h (6k)

646kB

QEMURAMD + QEMM

628kB

628kB

634kB

9E80h-A000h (6k)

634k

VMWare

Testcase

BDA

40h:13h

INT

12h

INT 15h,

AX=E820h

EBIOS

DATAAREA

Checkit 3.0

Plain DOS, after Boot

638kB

638kB

638kB

9F80h-A000h (2k)

640kB

HIMEM.SYS+EMM386.EXE

638kB

638kB

638kB

9F80h-A000h (2k)

640kB

QEMM

638kB

638kB

638kB

9F80h-A000h (2k)

640kB

QEMURAMD + QEMM

632kB

632kB

632kB

9F80h-A000h (2k)

634kB

Pentium 733

Testcase

BDA

40h:13h

INT

12h

INT 15h,

AX=E820h

EBIOS

DATAAREA

Checkit 3.0

Plain DOS, after Boot

639kB

639kB

639kB

9FC0h-A000h (1k)

640kB

QEMM

640B

640kB

639kB

D1B5h- (1k)

640kB

Attached documents:
MEQEMU.TXT QEMU, no CONFIG.SYS/AUTOEXEC.BAT
MEQEMUH.TXT QEMU, HIMEM.SYS, EMM386.EXE
MEQEMUQ1.TXT QEMU, QEMM386.EXE, NOXBDA parameter
MEQEMUQ2.TXT QEMU, QEMM386.EXE
MEVMW.TXT VMWare, no CONFIG.SYS/AUTOEXEC.BAT
MEVMWH.TXT VMWare, HIMEM.SYS, EMM386.EXE
MEVMWQ.TXT QEMU, QEMM386.EXE (XBDA not moved to HMA!?!)
P733.TXT, Pentium 733, no CONFIG.SYS/AUTOEXEC.BAT
P733Q.TXT Pentium 733, QEMM386.EXE

Code and Patches can be found at (released under GPL V2):
http://www.wiesinger.com/opensource/seabios/meminfoa.asm
http://www.wiesinger.com/opensource/seabios/meminfo.c
http://www.wiesinger.com/opensource/seabios/meminfo.exe
http://www.wiesinger.com/opensource/seabios/seabios-0.6.0-gw-V01.patch
QEMURAMD: DOS Device driver, which modifies BDA reported memory by -6kB, released later.

Build script will be released under my DOS-Tools soon (some cleanup necessary).

Ciao,
Gerhard