[Qemu-devel] Re: QEMU regression problems - Update FPU

[Gerhard Wiesinger]

Hello,

Good news: Seems to be that 2 of 3 issues have been fixed with QEMU: :-)
Summary of previous discussion:
http://www.mail-archive.com/address@hidden/msg29465.html

2.) Realtime clock: fixed
3.) Base Memory: fixed

Issue 1.) with FPU still present
I tracked down the problematic code and it is a rounding error from double 
precision to 64bit floats: Any ideas how to fix such an issue in general?

QEMU result in ST0: 0.42925860786976457 (wrong emulated)
KVM result in ST0:  0.42925860786975449 (correct)

Code:
        fninit                  ; init FPU
        fld1                    ; Pushes 1 on the stack, ST0=1
        fadd    st(0), st(0)    ; ST0=ST0+ST0=2
        fld1                    ; Pushes 1 on the stack, ST0=1, ST1=2
        fadd    st(1), st(0)    ; ST1=ST1+ST0=3, ST0=1
        fdivrp  st(1), st(0)    ; ST0=ST0/ST1=1/3
        f2xm1                   ; ST0=2^ST0-1 (ST0 must be in range -1 to 
+1)=2^(1/3)-1=0.25992104989487316476721060727823
        fldpi                   ; pushes pi on the stack; ST0=pi, 
ST1=0.25992104989487316476721060727823
        fyl2x                   ; 
ST0=ST1*log2(ST0)=0.25992104989487316476721060727823*1.651496129472318798043279295108=0.42925860786976448643152122341584
        fwait                   ; wait

*.ASM/*.COM file is also present for debugging.

Thnx.

Ciao,
Gerhard

--
http://www.wiesinger.com/


On Mon, 12 Apr 2010, Gerhard Wiesinger wrote:

> Hello,
>
> Checkit reports some problems under DOS:
> 1.) NPU functions are not correct: NPU Trigonometric Functions: FAILED. Seems 
> to be a problem of the instruction set.
> 2.) Real-Time Clock Alarm: FAILED (This might be also the reason for the
> KVM problem, see my previous post). Seems to be that real-time clock is not 
> working correct.
> 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.
>
> Details are listed below.
>
> All issues are NOT present under VMWare Server 2.0 and with real hardware.
>
> QEMU: 0.12.3 under Fedora 11, 2.6.30.10-105.2.23.fc11.x86 on AMD Phenom II 
> Quad Core, x86_64-softmmu.
>
> Any comments?
>
> Thnx.
>
> Ciao,
> Gerhard
>
> --
> http://www.wiesinger.com/
>
> Details:
> 1.)
>    NPU Trigonometric Functions.................................FAILED ***
>        Step 1, Expected    0.42926, received    0.42926
>
> Double 'Npu_oldans1' = 0.429259 (3FDB78F91894EFA5h).
> Double 'Npu_oldans2' = 0.628319 (3FE41B2F769CF0E0h).
> Double 'Npu_result ' = 0.429259 (3FDB78F91894EFA6h).
>
> 2.)
> Compare Current Time............................................Passed
>    DOS: 16:24:39.89    Real-Time Clock: 16:24:39.00   (.89 apart)
>
> Compare Current Date............................................Passed
>    DOS: 04/11/2010     Real-Time Clock: 04/11/2010.
>
> Real-Time Clock Alarm...........................................FAILED ***
>
> Compare Elapsed Time............................................Passed
>    DOS: 11.97 Seconds  Real-Time Clock: 12.00 Seconds   (.03 apart)
>
> 3.)     Known Memory:
>        Base        646K   From      0K to    646K   (0000000h to 00A17FFh)
>    Base Memory.................................................FAILED ***
>        ERROR at Address   0A0000h, Bits FEDCBA9876543210
>        ERROR at Address   0A0004h, Bits FEDCBA9876543210
>        ERROR at Address   0A0006h, Bits FEDCBA9876543210
>        ERROR at Address   0A0008h, Bits FEDCBA9876543210
>        ERROR at Address   0A000Ah, Bits FEDCBA9876543210
>        ERROR at Address   0A000Ch, Bits FEDCBA9876543210
>        ERROR at Address   0A000Eh, Bits FEDCBA9876543210
>        ERROR at Address   0A0010h, Bits FEDCBA9876543210
>        ERROR at Address   0A0012h, Bits FEDCBA9876543210
>        ERROR at Address   0A0014h, Bits FEDCBA9876543210
>        ERROR at Address   0A0016h, Bits FEDCBA9876543210
>        ERROR at Address   0A0018h, Bits FEDCBA9876543210
>        ERROR at Address   0A001Ah, Bits FEDCBA9876543210
>        ERROR at Address   0A001Ch, Bits FEDCBA9876543210
>        ERROR at Address   0A001Eh, Bits FEDCBA9876543210
>        ERROR at Address   0A0020h, Bits FEDCBA9876543210
>        ADDITIONAL MEMORY ERRORS WERE NOT LISTED DUE TO LACK OF SPACE.