ppc405 floating point emulation

ppc405 floating point emulation

[Jon Masters]

Hi there,

Can someone tell me what they think the status of the mathemu on ppc405
currently is? I am faced with a situation in which we will probably
require some kind of library or kernel emulation support and all around
people suggest not to even go there :-).

Cheers,

Jon.


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Re: ppc405 floating point emulation

[Wolfgang Denk]

In message <3FC4BACC.6000606@jonmasters.org> you wrote:
>
> Can someone tell me what they think the status of the mathemu on ppc405
> currently is? I am faced with a situation in which we will probably
> require some kind of library or kernel emulation support and all around
> people suggest not to even go there :-).

Library support (i. e. using "-msoftfloat") works fine.

Kernel emulation is available, but makes little sense to use as it is
awfully slow.

Best regards,

Wolfgang Denk

--
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd@denx.de
panic: kernel trap (ignored)

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Re: ppc405 floating point emulation

[Jon Masters]

Wolfgang Denk wrote:

> Library support (i. e. using "-msoftfloat") works fine.

Yes good. I had thought it would be fine to use that.

> Kernel emulation is available, but makes little sense to use as it is
> awfully slow.

The problem I have with this kernel is that floating point emulated
instructions which perform stores seem to be falling over. There is
a bug in the fault handling code for stock 2.4.21 that I am using it
would seem but am looking at whether it is worth fixing it.

By all accounts I might as well just use the floating point emulation in
libc but am still interested in enlightened feedback.

Cheers,

Jon.


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Re: ppc405 floating point emulation

[Toni Van Remortel]

Op wo 26-11-2003, om 15:38 schreef Jon Masters:
> Hi there,
>
> Can someone tell me what they think the status of the mathemu on ppc405
> currently is? I am faced with a situation in which we will probably
> require some kind of library or kernel emulation support and all around
> people suggest not to even go there :-).

That's what they told me too, but I did go there. And the result is
still quite good.
I'm currently writing the last documentation on our laser-projector.
This projects figures which are calculated by sin and cos together with
a pow function. Off course, we used lookup-tables and approx-functions,
but it works pretty well. Yesterday was the big show of it, and most
people liked it.

Anyhow, I use it in combination with real-time, and you cannot rely on
float calculations then. So you need a good implementation to get full
result of it.

Calculation isn't very fast, but on half a second, my module calculates
360 X and Y coordinates with 2 sin, 2 cos and 3 pow functions each
point.

So it is possible to use softfloat, but you MUST know that you cannot
rely on speed then. So far my small experience with it :)

PS: next week, I hope the docs will be ready and available on my website
under 'cases'/'our case'.

Regards,
--
                           Toni Van Remortel
              Wetenschappelijk Medewerker - D-science lab
  Real time Linux for embedded systems: http://linemb.d-sciencelab.com
              Tel: +32 3 205 61 72 - Fax: +32 3 205 61 95
                      E-mail: t.vanremortel@ha.be


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