andy pugh wrote: > I am completely baffled by this, and at the same time trying to advise > someone on the forum on the subject (blind leading the blind). > > He seems to think he can run userspace code, unmodified, in realtime > using rt-preempt. > Does this mean that rt-preempt removes the need for realtime threads > in HAL? Does HAL still work in that case? (and if so, how?) > I'm not an expert, but the preempt kernel (and a few others) take a completely different method of running real time threads. RTAI and rt-linux ran them as loadable kernel modules. rt-preempt leaves them as ordinary Linux processes under the usual user memory environment, but adds a different scheduler and interrupt handler to manage them under real time requirements. This has both advantages (mostly memory protection, debugging and crash handling) and disadvantages (access to physical hardware and special care to not call any service that breaks out of the real time mode). There are still real time threads that have to be scheduled. I think that part looks pretty similar.
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