Re: [ECOS] Floating Point Register saves

[Nick Garnett <nickg at ecoscentric dot com>]

David Brennan <eCos@brennanhome.com> writes:

> Nick Garnett wrote:
> >It should still work. The interrupt disable only blocks external
> >interrupts, the FPU unavailable exception is not blocked by this.
> >
> We found that the compiler was doing something funky with our virtual
> tables. We changed our compile options and removed the -fvtable-gc and
> that problem has gone away.

More recent compiler versions seem to have broken that and it is now
recommended that this option be removed. 

> However, now we get an occasional SIGILL
> after running for a while with Lazy FPU on. (Program stops at pc
> $000000008 and the backtrace cannot show how it got there.) With Lazy
> FPU off, we have no problems.

Looks like a jump to zero. Maybe stack corruption/overflow caused by
FP save/restore, or something?

> >However, lazy FPU switching is intended to work in ISRs, all the code
> >is in place. I suspect that there is a fairly simple reason for it not
> >working at present. That SIGFPE you see should be cought by the FP
> >switch handler and not get passed back the RedBoot. It is probably
> >still simpler to find out why that is not working.
> >
> We probably will not pursue this. However, if we decide to dig in,
> where exactly would this be happening.

The code is in a set of macros in arch.inc and the FP unavailable
handler in vectors.S. There's not much of it, so it should be easy to
understand.


-- 
Nick Garnett                    eCos Kernel Architect
http://www.ecoscentric.com/     The eCos and RedBoot experts


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