Re: [ECOS] Question about Stack usage in eCOS ? Thanks

[Nick Garnett <nickg at ecoscentric dot com>]

"Qiang Huang" <jameshq@liverpool.ac.uk> writes:

> Hi:
> 
> Q1:
>    I just wonder the exact meaning of using a seperate stack for interrupt
> handling? Is that mean: all the interrupts handling will be in its own stack
> rather than the user thread's stack? (Is this correct for all targets?)

Yes.

> 
> Q2:
>    Is the thread context switching happens after **exiting**(?) the clock
> ISR and uses the old thread's stack rather than the interrupt handler's
> stack? (Is this correct for all targets?)
>

Yes.

It is not essential that a HAL implements the interrupt stack and
those that do have a configuration option
(CYGIMP_HAL_COMMON_INTERRUPTS_USE_INTERRUPT_STACK) to control whether
it is enabled. If a HAL does not implement the interrupt stack, then
thread stacks must be large enough to accommodate all ISRs and DSRs
that might be called.

> Q3:
>   Is the following correct or not?(My assumption)
> 
> (Uses seperate interrupt stack)
> 
> 1). The hightest avaliable Thread (thread_A) get excuted by
> HAL_THREAD_LOAD_CONTEXT() (so on thread_A's stack correct??)
> --> 2). clock interrupt (Enter ISR and uses the Interrupt's stack correct??)
> --> 3). Exit from clock ISR (stack for interrupt handling will be unwinded
> back correct??)then stack switch back to thread_A's stack correct??

So far so good.

> --> 4). DSR invoked (now uses thread_A's stack correct??)
> --> 5). rtc->tick() invoked ( on thread_A's stack correct??)

If the HAL implements an interrupt stack, then the DSR will be
executed on that. See the diagram I posted for the exact set of steps.

> --> 6). HAL_THREAD_SWITCH_CONTEXT()  invoked ( so up to this point the
> thread context for thread_A will be saved to thread_A's stack right (does
> this includes??) and thread_B's thread context get restored from thrad_B's
> stack right??
> --> 7). branch to the thread_B's execution context.
>

Correct.


-- 
Nick Garnett - eCos Kernel Architect
http://www.eCosCentric.com/


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