MVME5500 broken with gcc-4.0.2

[Till Straumann]

Peter Dufault wrote:

>
> On Oct 31, 2005, at 6:05 PM, Till Straumann wrote:
>
>
>> WARNING:
>>
>> rtems/gcc (implicitely) uses -maltivec on all 74xx CPUS and
>> the MVME5500 calls for -mcpu=7450.
>>
>> Unfortunately, with -maltivec, gcc uses vector registers for
>> some optimizations.
>>
>> --> until proper altivec support is implemented in RTEMS random
>>     *data corruption* must be expected.
>>
>> Workaround:
>>
>> make/custom/mvme5500: use -mcpu=750
>>
>> -- Till
>>
>>
>>
>
> I've been using the mvme5500 24/7 using an earlier rev of gcc 4.0 in  
> a heavily floating point control application, with optimization on,  
> with a similar gcc configuration.  I don't explicitly use the  
> altivec.  I assume you're saying that gcc is using the vector  
> registers for data movement but RTEMS isn't saving / restoring them  
> and that's where the problem should come in,

yes

> but I'm not noticing any  problems.

It's nasty because probability for corruption can be very low but >0. A 
context switch must happen
while a vector register is in use and the register must be modified by 
another task.

Hopefully, MSR_VE should be off at startup so you would incur an 
exception (happens to me)
at an attempt to use vector registers.

T.

>   I've got lots of multi-axis floating point control going  on and a 
> heavy network load.  Did anything change in newer 4.0.x  releases?  
> I've built everything with 4.0.2 but haven't run things yet.
>
> Peter
>
>
>