Re: [Xenomai-core] Problem with periodic timer on PPC40x solved

[Wolfgang Grandegger <wg@domain.hid>]

Niklaus Giger wrote:
> Am Dienstag, 26. September 2006 22:23 schrieb Wolfgang Grandegger:
>> Niklaus Giger wrote:
>>> Am Dienstag, 26. September 2006 18:28 schrieb Wolfgang Grandegger:
>>>> Philippe Gerum wrote:
>>>>> On Tue, 2006-09-26 at 16:56 +0200, gilles.chanteperdrix wrote:
>>>> OK, but in general, soft-float emulation should be used on systems
>>>> without FPU and this is even more important for real-time. This is a
>>>> tool chain issue. Niklaus, what tool chain are you using?
>>> In my .config I have
>>> MATH_EMULATION=y
>> You seem to need that because your compiler generates code with hard FP
>> instructions. You could check this with:
>>
>>   $ ppc-linux-objdump -d prog|egrep ":\s*[e-f]"
> This does not return any match on my system.

Oops, then your compiler seems _not_ to create hard FP instruction, 
otherwise you would get:

   ppc_82xx-objdump -d latency|egrep ":\s*[e-f]"
   latency:     file format elf32-powerpc
   100036ac:       fc 21 f8 28     fsub    f1,f1,f31
   100036b4:       fc 42 f8 28     fsub    f2,f2,f31
   100036c4:       fc 63 f8 28     fsub    f3,f3,f31
   100036cc:       fc 21 f0 24     fdiv    f1,f1,f30
   100036dc:       fc 84 f8 28     fsub    f4,f4,f31
   ...

> But looking at the disassembly of the latency program I have code like:
> 100081bc <_restfpr_28_x>:
> 100081bc:       cb 8b ff e0     lfd     f28,-32(r11)
> or
> 1000798c <__floatsidf>:
> 1000798c:       7c 08 02 a6     mflr    r0
> 10007990:       2f 83 00 00     cmpwi   cr7,r3,0
> 10007994:       94 21 ff c0     stwu    r1,-64(r1)
> 10007998:       90 01 00 44     stw     r0,68(r1)
> 1000799c:       54 60 0f fe     rlwinm  r0,r3,1,31,31
> 100079a0:       90 01 00 14     stw     r0,20(r1)
> 100079a4:       40 9e 00 24     bne-    cr7,100079c8 <__floatsidf+0x3c>

That's from soft float emulation.

>>> The toolchain is gcc-3.4.4-glibc-2.3.5/powerpc-405-linux-gnu built using
>>> Dan Kegel crosstool (Version 0.42 if I remember exactly).
>>>
>>> Shall I switch to another one?

Maybe (likely) there is nothing wrong with your tool chain.

>> The ELDK from DENX uses FP soft-emulation for 4xx (http://www.denx.de).
>> Choose  v3.1.1 for Linux 2.4 and v4 for Linux 2.6.
> 
> I am breathing only PowerPC code on my Mac PowerBook (running Debian) and 
> never managed to installed ELDK on it. (And even Detlev as a Debian developer 
> couldn't recommend a simple way.) 

I remember Detlev's pain and frustration.

> But I assume that I specifying GLIBC_EXTRA_CONFIG="--without-fp" in the 
> powerpc-405.dat should be enough to make Dan Kegels crosstool emit Soft-FPU 
> emulation.

See above.

> I will try to run the tests at work where I have installed ELDK 4.0, but not 
> yet a fully working environment. Therefore it may take some time to report a 
> result back.

I'm now a bit puzzled why a FP exception occurs. What happens if you 
disable MATH_EMULATION
in your kernel (that's what I normally have). It will try the latency 
test on my Walnut-Board with CONFIG_XENO_OPT_DEBUG asap.

Wolfgang.