floating point operation of ppc

floating point operation of ppc

[lily]

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hi,all:
    i build an embedded linux on powerpc 405ep,i need execute floating point operation,and i enable "math emulate" option in kernel, i run a while(1)loop ,in the loop there was floating point expression ,after test ,i found the while (1) exit because of the floating point computation,that is the floating point can't execute on ppc stablely.Is there someone meets the same problems ,please give me some suggestion,thanks!!!

                                                                                                     lily 

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Re: floating point operation of ppc

[Greg Weeks]

lily wrote:

> hi,all:
> i build an embedded linux on powerpc 405ep,i need execute floating
> point operation,and i enable "math emulate" option in kernel, i run a
> while(1)loop ,in the loop there was floating point expression ,after
> test ,i found the while (1) exit because of the floating point
> computation,that is the floating point can't execute on ppc
> stablely.Is there someone meets the same problems ,please give me some
> suggestion,thanks!!!

The 405ep has some errata on floating point use. I didn't work on the
processor so I don't know exactly what they are, but Timesys has a
toolchain just for the 405ep to work around the problem. The other
workaround we've used is much slower and it involved disabling the
hardware floating point unit in the head.s for the 405ep and turning on
the emulator. Just turning on the emulator is insufficient. The Timesys
toolchain isn't the only one out there specifically for the 405ep.

Greg Weeks

Re: floating point operation of ppc

[Eugene Surovegin]

On Fri, Nov 11, 2005 at 07:51:31AM -0500, Greg Weeks wrote:
> lily wrote:
> 
> > hi,all:
> > i build an embedded linux on powerpc 405ep,i need execute floating
> > point operation,and i enable "math emulate" option in kernel, i run a
> > while(1)loop ,in the loop there was floating point expression ,after
> > test ,i found the while (1) exit because of the floating point
> > computation,that is the floating point can't execute on ppc
> > stablely.Is there someone meets the same problems ,please give me some
> > suggestion,thanks!!!
> 
> The 405ep has some errata on floating point use. 

Are you sure it was 405ep? There is no floating point errata for this 
chip due to the simple reason, it doesn't support floating point in 
hardware at all.

You probably confusing it with 440ep.

I'm not aware of any 405ep specific toolchain. In fact, all what is 
needed is simple 4xx specific toolchain with soft-float enabled by 
default. This is how floating point is usually done for 4xx - just soft 
emulation in user-space by the compiler without in-kernel emulation, 
which is slow.

-- 
Eugene

Re: floating point operation of ppc

[Greg Weeks]

Eugene Surovegin wrote:

>On Fri, Nov 11, 2005 at 07:51:31AM -0500, Greg Weeks wrote:
>  
>
>>lily wrote:
>>
>>    
>>
>>>hi,all:
>>>i build an embedded linux on powerpc 405ep,i need execute floating
>>>point operation,and i enable "math emulate" option in kernel, i run a
>>>while(1)loop ,in the loop there was floating point expression ,after
>>>test ,i found the while (1) exit because of the floating point
>>>computation,that is the floating point can't execute on ppc
>>>stablely.Is there someone meets the same problems ,please give me some
>>>suggestion,thanks!!!
>>>      
>>>
>>The 405ep has some errata on floating point use. 
>>    
>>
>
>Are you sure it was 405ep? There is no floating point errata for this 
>chip due to the simple reason, it doesn't support floating point in 
>hardware at all.
>
>You probably confusing it with 440ep.
>
>  
>
You're right. It was the 440ep. The 405ep BSP is using the 4xx 
toolchain. I don't think I've ever tried the math emulator on a 405.


Greg Weeks