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Is it correct to store MSR in context switch?
- Date: Thu, 24 Jan 2002 09:45:56 +0100
- From: valette at crf.canon.fr (VALETTE Eric)
- Subject: Is it correct to store MSR in context switch?
> Hello, all.
> I encountered the following problem (MPC860, RTEMS 20001201 but this seems
> to be not touched):
> The Machine Status Register is saved each time the context switch is
> performed. This leads to the following unexpected result - if in one task the
> _ISR_Disable(arg) is used, it may be neutralized by the task switch. One can
> say, that this is very unusual thing to disable interrupts in the running
> system still doing task switching. But this is not an impossible case - I
> need it :-)).
> Will it cause any harm if the MSR register will not be saved in context
> switches? It does not seem to contain any task specific information...
Yes this will in general : the MSR status is a thread attribute that
shall not be lost. It contains for example the FP status (enabled
disabled, single stepping) that you cannot lost when switching back.
/ ` Eric Valette - Canon CRF
/-- __ o _. Product Dev. Group Software Team Leader
(___, / (_(_(__ Rue de la touche lambert
35517 Cesson-Sevigne Cedex
Tel: +33 (0)2 99 87 68 91 Fax: +33 (0)2 99 84 11 30
E-mail: valette at crf.canon.fr http://www.crf.canon.fr