RT PREEMPT patches?

Hi,

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I feel that doing SMP System code for NIOS is a real challenge, as NIOS does not fave atomic instructions. I did some research on how it could be possible to provide a kind of Mutex with custom instructions that could be used to protect instruction sequences to make them atomic. I suppose this is possible and extensible to multiple CPUs, but you do need additional "hardware" to do this and I did not exactly proof that it might work.

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Several CPUs make 'Mutex' by using atomic instructions. But both for SMP system and CONFIG_PREEMPT_RT, we only need the 'Mutex' mechanism, not atomic instructions. And I don't think that we can make 'Mutex' by using custom instructions because there is no information about interrupt acception timing, pipeline behaviors and custom instructions.

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Do you think this is needed to apply the CONFIG_PREEMPT_RT patch ?

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We must enable the interruption in the critical section, so we need some kind of 'Mutex'.

Kazu