[ECOS] ref to previous question-'calling path questions, thanks'

Qiang Huang jameshq@hotmail.com
Mon Oct 2 15:33:00 GMT 2006


Thanks a lot for your help Bart.

But inside IRQ (vector.s) what does pre-exception mode points to? (Is that 
always supervisor mode prior to entering IRQ mode? (if it is supervisor mode 
for pre-exception mode, what is difference between saving pre-exception mode 
context and what will be saved later on in hal_switch_context function?)




>From: Bart Veer <bartv@ecoscentric.com>
>To: jameshq@hotmail.com
>CC: ecos-discuss@sourceware.org
>Subject: Re: [ECOS] ref to previous question-'calling path questions, 
>thanks'
>Date: 01 Oct 2006 16:59:13 +0100
>
> >>>>> " " == Qiang Huang <jameshq@hotmail.com> writes:
>
>      > Hi eCOS experts:
>      >    Maybe my previous question
>      > (http://ecos.sourceware.org/ml/ecos-discuss/2006-09/msg00231.html) 
>is a
>      > little confusing, what it really means is the followings:
>
>      > (ARM target)
>      > Two thread #1 and #2 exist in system
>
>      > (1) Thread #1 runs first
>      > (2) Thread #1 issues SWI instruction
>      > (3) Enter SWI ISR and run on thread #1 stack (svc mode)
>      > (4) At the time IRQ occurs and preempts SWI ISR
>      > (5) Switch SVC and run on thread #1 stack (svc mode)
>      > (6) Eventually comes to interrupt_end() and unlock_inner(), which 
>will cause
>      > a context switching
>      > (7) Thread #2 context is loadded and return with thread #2 running
>
>      > Here seems SWI is preempted by thread #2? Is this correct?
>      > (shouldn't all ISR be finished before any thread has the chance to 
>run?)
>
>      > Hope someone can give me some hint, that would be very
>      > thankful.
>
>eCos does not use SWI's. The main purpose of the SWI instruction is to
>provide a controlled mechanism for switching between user mode and
>supervisor mode, but eCos applications always run in supervisor mode
>so there is no need for a switch. If for some obscure reason an
>application does execute a SWI instruction the resulting system
>behaviour is basically undefined.
>
>Bart
>
>--
>Bart Veer                       eCos Configuration Architect
>http://www.ecoscentric.com/     The eCos and RedBoot experts

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