tasks blocking

Ilya Alexeev ilya at continuum.ru
Mon Dec 3 09:38:32 UTC 2001

Hi RTEMS users & developers.

Some time ago I wrote a similar letter but I have not received any answer so 

I am using gen68360 bsp & rtems-ss-20011025
and I have noticed the following problem:

When creating a task with RTEMS_INTERRUPT_LEVEL which is less than the
interrupt level of the Periodic Interrup Timer (PIT), then after calling
the directive rtems_task_wake_after this task may not wake up, the
probability being very high.

If we create the task with RTEMS_INTERRUPT_LEVEL greater or equal to
PIT interrupt level, the directive rtems_task_wake_after works "better";
however, there have been occasions when after several days of continuous
testing this task stopped forever.

What may this problem be caused by?

Here is the test I have been using.

//////////////// begin ////////////

rtems_task testTask(rtems_task_argument ignored)

rtems_task Init(rtems_task_argument argument)
    int i;
    rtems_id tid;

    puts("Test is running...");

    for (i = 0; i < 10; i++)
	rtems_task_start(tid, testTask, 0);


//////////////// end ////////////

The getchar() function in Init doesn't block the testTasks and doesn't
influence test results.

No combination of task modes and task attributes influences test
results. Everything depends upon RTEMS_INTERRUPT_LEVEL.

Here are the results of CPU_usage_Dump() after some time of testing.

CPU Usage by thread
   ID        NAME        TICKS
0x04010001   IDLE      11251
0x08010001   INIT       4523
0x08010002   TSK0        513
0x08010003   TSK1         31
0x08010004   TSK2        514
0x08010005   TSK3         37
0x08010006   TSK4         18
0x08010007   TSK5         18
0x08010008   TSK6         20
0x08010009   TSK7         32
0x0801000a   TSK8       6217
0x0801000b   TSK9        512

Ticks since last reset = 5823

Total Units = 23480

As you see, some tasks have lost their control very quickly.

I will be glad to receive any replies and ideas.


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