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

[Wolfgang Grandegger <wg@domain.hid>]

Wolfgang Grandegger wrote:
> 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.

I'm unable to reproduce the problem of our Sycamore board with Linux 2.6.14:

   CPU:   AMCC PowerPC 405GPr Rev. B at 333.333 MHz (PLB=133, OPB=66,
          EBC=66 MHz)
          Internal PCI arbiter enabled, PCI async ext clock used
          16 kB I-Cache 16 kB D-Cache
   Board: Sycamore - AMCC PPC405GPr Evaluation Board

Wolfgang.