Why are only some of the registers stored when making a context switch.

[wmjenkinson]

Why are only some of the registers stored when making a context switch? Is it possible to switch tasks in and out of different cpu cores using the example taskswicth();???

Thank you.

[rsta2]

The scheduler in Circle is cooperative and task switches can only happen, when a C or C++ function gets called. That's why TaskSwitch() is implemented as a function too, and thus only needs to save the registers, which have to be saved inside of a C function. For performance reasons other registers are not saved.

The Circle scheduler and its tasks always run on core 0. The other cores are free for other things. So normally no, you cannot run tasks on core 1-3.

[wmjenkinson]

I'm thinking of re-writing the scheduler example to support multiple cores. The plan is to simply fire up the cores which then begin taking tasks of the ready list. I also think I'll need to save more registers in the task context switch.

[rsta2]

I extended the scheduler earlier, so that it was running on all available cores. But it was not possible to move a task from one to another core in this setup. I did not completed this, because it added a lot of complexity, but was not really useful.

For a cooperative scheduler I think it's not necessary to save more registers. For a preemptive scheduler it would be, but Circle is not really prepared for this. Most functions are not re-entrant.

[wmjenkinson]

One last point, is there a function that returns the cpu id?

[rsta2]

Does this help?