FP context switching on i386

Thomas Doerfler Thomas.Doerfler at embedded-brains.de
Sat Oct 3 19:47:08 UTC 2009

Eric Valette schrieb:
> Till Straumann wrote:
>> Thomas Doerfler wrote:
>>> Till,
>>> although I am not at all familiar with i386 ABI stuff, I would guess
>>> that we have to save the context during a task switch, at least when it
>>> was forced due to a interrupt (e.g. timer) event. In these cases there
>>> is no function call involved for the function that uses the FP context.
>> I think you're right, Thanks.
> The most efficient way is to do  is lasy FP saving: you disable the 387
> while noting the task that was using it and get an exception is someone
> wants to use FPU registers...

Sebastian is currently implementing this for PowerPC in the current
environment. It is a bit tricky to make sure that the FPU stays disabled
when restoring a previously saved MSR :-)

How is the FPU controlled in i386?


> -- eric
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