Floating Point Operation in Kernel

Floating Point Operation in Kernel

[jimmy liu]

I am writing a module which need be integrated to the
linux kernel with floating point operations for
mpc82xx. The kernel does not provide support for
floating point operations. Does anybody have good idea
to implement it or make it to work around?



 
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Re: Floating Point Operation in Kernel

[Grant Likely]

On 12/12/06, jimmy liu <jimmyzhmliu@yahoo.com> wrote:
> I am writing a module which need be integrated to the
> linux kernel with floating point operations for
> mpc82xx. The kernel does not provide support for
> floating point operations. Does anybody have good idea
> to implement it or make it to work around?

The official answer is: "Don't do that."  :)

Here's the more generous reply:  The kernel explicitly does not
support floating point in the kernel.  Save/restore on floating point
registers is expensive.  In fact, IIRC, floating point registers for
user space use 'lazy save/restore'; ie. the registers are not saved on
every context switch; they are only saved if another user space
process tries to perform FP operations.

To support FP access in kernel space means you must fit your code into
the already complex FP save/restore state machine; or you need to
disable all interrupts and perform your own FP register save/restore
within the context of your driver.  And it's a pretty safe bet that
you'll have trouble getting the driver into mainline.

Why do you need kernel space FP?

-- 
Grant Likely, B.Sc. P.Eng.
Secret Lab Technologies Ltd.
grant.likely@secretlab.ca
(403) 399-0195

Re: Floating Point Operation in Kernel

[Carlos Munoz]

jimmy liu wrote:

>I am writing a module which need be integrated to the
>linux kernel with floating point operations for
>mpc82xx. The kernel does not provide support for
>floating point operations. Does anybody have good idea
>to implement it or make it to work around?
>
>
>
> 
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>Yahoo! Music Unlimited
>Access over 1 million songs.
>http://music.yahoo.com/unlimited
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>Linuxppc-embedded mailing list
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>  
>
What exactly is the floating point operation you need to implement ?


Carlos

-- 
There are two rules for success in life:
1) Never tell everything you know.

Re: Floating Point Operation in Kernel

[jimmy liu]

We has a hardware driver need the floating point
operation to do timing recover. Maybe, we have to do
it in user space.

--- Carlos Munoz <carlos@kenati.com> wrote:

> jimmy liu wrote:
> 
> >I am writing a module which need be integrated to
> the
> >linux kernel with floating point operations for
> >mpc82xx. The kernel does not provide support for
> >floating point operations. Does anybody have good
> idea
> >to implement it or make it to work around?
> >
> >
> >
> > 
>
>____________________________________________________________________________________
> >Yahoo! Music Unlimited
> >Access over 1 million songs.
> >http://music.yahoo.com/unlimited
> >_______________________________________________
> >Linuxppc-embedded mailing list
> >Linuxppc-embedded@ozlabs.org
>
>https://ozlabs.org/mailman/listinfo/linuxppc-embedded
> >  
> >
> What exactly is the floating point operation you
> need to implement ?
> 
> 
> Carlos
> 
> -- 
> There are two rules for success in life:
> 1) Never tell everything you know.
> 
> 



 
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Re: Floating Point Operation in Kernel

[Ben Warren]

On Wed, 2006-12-13 at 08:20 -0800, jimmy liu wrote:
> We has a hardware driver need the floating point
> operation to do timing recover. Maybe, we have to do
> it in user space.
> 
Have you considered doing the math in fixed point instead?  I realize
that certain data sets make this difficult but this has been a standard
technique in resource-constrained systems forever.

regards,
Ben

Re: Floating Point Operation in Kernel

[Andrew E. Mileski]

jimmy liu wrote:
> I am writing a module which need be integrated to the
> linux kernel with floating point operations for
> mpc82xx. The kernel does not provide support for
> floating point operations. Does anybody have good idea
> to implement it or make it to work around?

How about my fixed point routines.  They use S31.32 fixed format, which
is often better precision than using floats, though it has less range.
Awkward to use, but handy when you absolutely need to.

I originally wrote it for MP3 decoding on ARM, but it should be
portable to anything supporting "signed long long" format (hence
the name).  http://cvs.isoar.ca/math-sll/

--
Andrew E. Mileski