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Task switching problem
- From: Yuriy Coureelo <coureelo at micran dot ru>
- To: ecos-discuss at sources dot redhat dot com
- Date: Fri, 1 Jul 2005 15:59:34 +0600
- Subject: [ECOS] Task switching problem
- Reply-to: Yuriy Coureelo <coureelo at micran dot ru>
Good Day!
eCos: v2.0-20030509-0835
Architecture: ARM, AT91
PROBLEM DESCRIPTION
There are 4 active threads: system idle thread, thread A working with
FIQ, thread B working with IRQ, high-priority thread C just blinking
a LED. Starting hardware I see blinking LED (good) and working threads
A and B (fine). System works from couple of seconds upto couple of
minutes, then LED stops blinking.
I tried to find out a reason lot of times, and had following common info:
01.FIQ incoming
02.ISR and DSR called, DSR posted flags for thread A
03.Scheduler takes a decision to switch from idle to thread A
04.IRQ incoming but scheduler works yet, so ISR called and DSR just
posted
05.Threads A start working but there is pending DSR (posted at step 04)
06.DSR called and posted flags for thread B
07.Scheduler takes a decision to switch from thread A to thread B
08.Thread B working and going to sleep
09.IRQ incoming but scheduler already works, so ISR called and DSR just
posted
10.Scheduler takes a decision to switch from thread B to thread A,
because thread B already sleeping, and IRQ (at step 09) posted DSR
a bit later than scheduler checks DSRs at its beginning
11.After switching scheduler checks for DSRs again and detects DSR,
posted at step 09:
if( Cyg_Interrupt::DSRs_pending() ) {
inc_sched_lock(); // reclaim the lock
continue; // go back to head of loop
}
12.DSR called and posted flags for thread B
13.Scheduler takes a decision to switch from thread A to thread B
(thread A didn't even continue)
14.Thread B working and going to sleep
15.Scheduler takes a decision to switch from thread B to thread A
16.Thread A working and going to sleep
17.Scheduler takes a decision to switch from thread A to idle
18.interrupt_end() at last exits,
Cyg_Scheduler::get_sched_lock() returns 0 (my checkpoint)
But idle thread isn't called.
When new interrupt comes, interrupt_end() exits because sched_lock
already equals 1, althoug no calls to inc_sched_lock() and
set_sched_lock().
No more interrupts come after that (i think cpu got somewhere away).
Stacks seems are OK (I have memory dump over JTAG).
I guess it is extremely hard to find a reason of the problem, but
would you point me where or what I should search, please.
Yuriy Coureelo
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