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M68k/ColdFire: FPU context initialization
- Date: Mon, 05 Nov 2007 11:22:22 -0700
- From: brett.swimley at aedbozeman.com (Brett Swimley)
- Subject: M68k/ColdFire: FPU context initialization
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.
Joel Sherrill wrote:
> Thomas Doerfler wrote:
>> 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 D?rfler.
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> rtems-users at rtems.com
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