[ECOS] question about starting point of thread context switching(sparc target)? Thanks

[Qiang Huang]

Hi all:
    could I get some help on this issue? Thanks a lot.  I have spent lots of
time in figuring out this but I am still quite confused.

Q1.
After the scheduler start the context of the thread with the highest
priority (called thread1)(or maybe ready thread) will be loaded and run so
it starts from its executing code(point). After a while interrupt happens
and another thread (called thread2) is made ready to run, so as follow:

(Note: here thread2 is the first time to run)

scheduler starts --> thread1 context loaded and runs --> interrupt happens
(makes thread2 ready to run the first time)--> default interrupt handler -->
dispatch to actual isr() --> call to interrupt_end( ) --> [ unlock( ) -->
unlock_inner( ) --> HAL_THREAD_CONTEXT_SWITCH( ) --> save the context of
thread1--> load the context of thread2 (the context is initialized by the
time a Cyg_Thread object is constructed)  --> jumps to thread2's executing
code?? right?? not return back to interrupt_end( ) or executing the rest
code in interrupt_end( )?? so it is **not** returns from the
default_isr_handler () int vec_ivsr.S, Am I wrong?? then the "rett" in the
very end of default_isr_handler( ) in vec_ivsr.S is not executed will that
be any problem??


Q2.
If both threads have already been started (not the first time to run) so
when the interrupt happens and make the thread context switching happens:
....... as Q1 -->  call to interrupt_end( ) --> [ unlock( ) -->
unlock_inner( ) --> HAL_THREAD_CONTEXT_SWITCH( ) --> save the context of
thread1--> load the context of thread2 --> returns to the next instruction
of HAL_THREAD_CONTEXT_SWITCH( ) in interrupt_end( ) (becauses the return
address saved in thread2's context is back to the next instruction of
HAL_THREAD_CONTEXT_SWITCH( ) in interrupt_end( ), because thread2 is ***not
the first time to run***. Is that right?? --> return from interrpt_end( )
back to default_isr_handler in vec_ivsr.S --> return back from
default_isr_handler( ) back to thread2's execution context
Is the above process for context switching correct??

Does that mean after the first time of each thread runs, after the thread
context switching the execution will returns back to the next instruction in
interrupt_end( )? if the next context switched thread is the first time to
run then the interrupt is

BTW because in sparc I also need to deal with register window and stack for
the interrupt and context switching, is there any way in understand the
insight the kernel operation (like thread context switching) easily.

Thanks a lot.





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