M68k/ColdFire: FPU context initialization

[Thomas Doerfler (nt)]

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Hi Brett,

thank you for the offer. But now we almost have a/the solution for the
FP context save/restore, so actually we would like to integrate our
solution.

We just want to make sure that we initialize things properly, that's why
I started this thread.

wkr,
Thomas.


Brett Swimley schrieb:
> It is a bit different.
> 
> I have a patch that saves and restores the FP context for the MCFv4e
> that I keep meaning to submit (based on the -mcfv4e compiler option
> found in the newer gcc compilers).  I will try to put that together. 
> 
> I will look at the FPU control register initialization.  I don't know if
> I did that.
> 
> On this topic, would it be possible to add the mcfv4e variant to the
> list of m68k targets (t-rtems) and include this in the pre-built RPMs? 
> I added this variant to my version of the compiler, but I don't know if
> I got all the soft-float stuff correct.
> 
> Brett
> 
> Joel Sherrill wrote:
> 
>>Thomas Doerfler wrote:
>>  
>>
>>>Hi,
>>>
>>>we are currently adding FPU support for a ColdFire v4e CPU derivate.
>>>After reading, re-reading (and reading again) the relevant files in
>>>cpukit/score/cpu/m68k in the current M68K (with hardware FPU, e.g.
>>>MC68040) CPU Context management, I have not found, where/how the FPU
>>>context is initialized for a newly created thread.
>>>
>>>Can somebody please guide me:
>>>
>>>- Is the FPU context in an arbitrary state when a new thread is started?
>>>  
>>>    
>>>
>>If the thread is not an FP task, you would prefer to disable the FPU.
>>If it is FP enabled, then all that you have to initialize is usually
>>the control registers.
>>  
>>
>>>- Or: Where is the code which defines the initial state of the FPU in a
>>>new thred?
>>>  
>>>    
>>>
>>
>>score/cpu/m68k/rtems/score/cpu.h and score/cpu/m68k/cpu_asm.S
>>
>>Is the Coldfire FPU similar to the 68881 or is it more RISC like?
>>Do you have the same type of fsave/restore instructions?
>>  
>>
>>>Any hint appreciated,
>>>
>>>Thomas Dörfler.
>>>
>>>
>>>
>>>  
>>>    
>>>
>>
>>_______________________________________________
>>rtems-users mailing list
>>rtems-users at rtems.com
>>http://rtems.rtems.org/mailman/listinfo/rtems-users
>>  
>>
> 
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> 
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IMD Ingenieurbuero fuer Microcomputertechnik
Thomas Doerfler           Herbststrasse 8
D-82178 Puchheim          Germany
email:    Thomas.Doerfler at imd-systems.de
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