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SubjectRe[2]: Kernels 2.1 with 386DX/387 IRQ13 PC boxes
  Hi,

Sorry for replying once for different people, but here is what I'd like
to say :

Alan wrote:
>> I have a problem with kernels since at least 2.1.46 and up to 2.1.59
>> with my 386DX33 (AMD compatible) and my 387 Cyrix FasMath CX83D87-33 GP
>> math coprocessor. I think the problem appears also with a standart
>> Intel 80386/80387 when IRQ13 is used.
>
>Turn off the SMP=1 in the top Makefile

OK, but if 386/387 IRQ13 PC can work with SMP defined, why not to
correct the kernel? I do not think it is easy to maintain 4 linux kernels,
taking into account that there is already the developpement tree and the
stable one.

>> Then, the kernel will boot ONLY if SMP is NOT defined at compile
>> time.
>
>Correct - IRQ 13 does something totally different in SMP mode. (BTW if
>someone is crazy enough to want to work on this some IBM dual 486 boards
>have 486SLC + FPU delivering a local IRQ 13 to each CPU) - we dont
>support that either

The IRQ13 synchronisation mecanism is not used for SMP (line 376 of
traps.c), and now an IRQ13 always call the math_error function or returns.

John Gotts wrotes :
>In any case, you should not be running an SMP kernel on a non-SMP
>machine. It isn't guaranteed to work and certainly it won't perform as
>well as a uniprocessor kernel in your configuration.

I also have a 2.0.31 kernel running, but to try developpments, why not
to use the lattest kernel ? Also maintainning 4 versions is difficult, as
previously stated.

Gabriel wrotes:
>unsigned short cw=0x340;
>asm volatile("fninit; fldcw %0; fld %%st; wait": : "m" (cw));
and
>main() {
> unsigned short cw;
> asm("fstcw %0": "=m" (cw):);
> printf("Initial FPU CW:%x\n", cw);
>}

Thanks, that is working and I will do more test. I just wonder why this
control word is not set when a program set a handler for SIGFPE (signal()
function) ?

Thanks for everyone,
Etienne.

-- Personnal E-mail : etienne.lorrain@ibm.net
------------- On ne voit bien qu'avec le coeur, --------------------
----- l'essentiel est invisible pour les yeux . St Exupery ---------


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