<p>Hi,</p>
<p>The most likely answer is that global variables in the stanford.c file are shared and not protected e.g. by semaphores.</p>
<div class="gmail_quote">On Oct 18, 2011 5:31 PM, "Constantine "chicky" Giotopoulos" <<a href="mailto:kotsosgiotopoulos@gmail.com">kotsosgiotopoulos@gmail.com</a>> wrote:<br type="attribution">
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="gmail_quote"><div class="gmail_quote">Hello everyone.<br><br>I am using RTEMS to create a number of tasks and run a set of functions performing mostly mathematical operations. These are included in a file named "stanford.c" ( <a href="http://classes.engineering.wustl.edu/cse465/docs/BCCExamples/stanford.c" target="_blank">http://classes.engineering.wustl.edu/cse465/docs/BCCExamples/stanford.c</a> ). The problem is that when I enable preemption, for some reason the functions do not output the expected results.</div>
<div class="gmail_quote"> </div>
<div class="gmail_quote">I initially create 100 tasks using the following lines of code:</div>
<div class="gmail_quote">----------------------------------------------------------------------------------------------------<br>rtems_task Init( rtems_task_argument ignored )<br>{<br> rtems_status_code status; rtems_id id;<br>
int i;<br><br>for (i=0;i<100;i++)<br>{<br> srand(i*3); <br><br> status = rtems_task_create(<br> rtems_build_name( 'T', 'A', '2', ' ' ), rand()%254+1,<br> RTEMS_MINIMUM_STACK_SIZE, RTEMS_DEFAULT_MODES,<br>
RTEMS_DEFAULT_ATTRIBUTES | RTEMS_FLOATING_POINT, &id<br> );<br> assert( !status );<br><br> status = rtems_task_start( id, task2, id%1000 );<br> assert( !status );<br>}<br><br> status = rtems_task_delete( RTEMS_SELF );<br>
<br> exit( 0 );<br>} <br>-----------------------------------------------------------------------------------------------------------------------------<br>Then I state the functionality of the tasks.Each task executes the functions included in the "stanford.c" 5 times using a "for" loop. Each task is triggered with a "wake_after" directive that is set randomly before each execution and the priority is changed also randomly after each execution.The point in that is to get various tasks triggering at a random manner and taking over the CPU in a (somewwhat) random way:<br>
---------------------------------------------------------------------------------------------------------------------------<br>rtems_task task2( rtems_task_argument id_arg )<br>{<br> rtems_status_code status;<br> int i;<br>
<br> for (i=0;i<5;i++)<br> {<br> srand(id_arg*i);<br> rtems_task_wake_after(rand()%1000);<br> printf("Task2-stanford with id=%d is executing. Iteration:%d\n", id_arg, i);<br> stanford(); <br>
printf("Task2-stanford with id=%d iteration:%d has finished.\n\n\n", id_arg, i);<br> <br> rtems_task_set_priority(RTEMS_SELF, rand()%254+1, 1);<br> }<br> rtems_task_delete( RTEMS_SELF );<br>
}<br><br>My configuration options are:<br>#define CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER<br>#define CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER<br>#define CONFIGURE_RTEMS_INIT_TASKS_TABLE<br>#define CONFIGURE_MICROSECONDS_PER_TICK 100<br>
#define CONFIGURE_MAXIMUM_TASKS 105<br>#define CONFIGURE_INIT<br>#include <rtems/confdefs.h><br>--------------------------------------------------------------------------------------------------------------------------</div>
<div class="gmail_quote">I have attached the code that is being executed (test.c-makefile)<br><br>If I enable non-preemption, then the execution output is as expected, no error messages or anything out of the ordinary, for example:<br>
------------------------------------------------------------------------------------------------------------------------<br>Task2-stanford with id=698 is executing. Iteration:0 <br>Starting <br> Perm Towers Queens Intmm Mm Puzzle Quick Bubble Tree FFT <br>
0 0 0 0 0 0 0 0 0 0 <br> <br>Nonfloating point composite is 0 <br> <br>Floating point composite is 0 <br>Task2-stanford with id=698 iteration:0 has finished. <br>
<br> <br>Task2-stanford with id=714 is executing. Iteration:0 <br>Starting <br> Perm Towers Queens Intmm Mm Puzzle Quick Bubble Tree FFT <br> 0 0 0 0 0 0 0 0 0 0 <br>
<br>Nonfloating point composite is 0 <br> <br>Floating point composite is 0 <br>Task2-stanford with id=714 iteration:0 has finished. <br> <br> <br>Task2-stanford with id=730 is executing. Iteration:0 <br>
Starting <br> Perm Towers Queens Intmm Mm Puzzle Quick Bubble Tree FFT <br> 0 0 0 0 0 0 0 0 0 0 <br> <br>Nonfloating point composite is 0 <br>
<br>Floating point composite is 0 <br>Task2-stanford with id=730 iteration:0 has finished.<br><br>However, when I enable preemption, tasks start interrupting each other (depending on their priority). Especially when it comes to functions that use recursion, I am presented with errors. These do not occur everytime these functions are executed, but occasionally. These errors occur mostly when a task is interrupted by another task(s) of higher priority. The error messages are somewhat like that:<br>
" Perm Towers Error in Towers: nothing to pop <br> Error in Towers: nothing to pop <br> Error in Towers: disc size error <br> Error in Towers: disc size error <br> Error in Towers: nothing to pop <br> Error in Towers: nothing to pop <br>
Error in Towers: disc size error"<br><br>"Task2-stanford with id=714 is executing. Iteration:2 <br>Starting <br>Task2-stanford with id=745 is executing. Iteration:3 <br>Starting <br> Perm Towers Queens Intmm Mm Puzzle Quick Bubble Tree FFT <br>
0 0 0 0 0 0 0 0 0 0 <br> <br>Nonfloating point composite is 0 <br> <br>Floating point composite is 0 <br>Task2-stanford with id=745 iteration:3 has finished. <br>
<br> <br> <strong> Perm Error in Perm. <br></strong> Towers Queens Intmm Mm Puzzle Quick Bubble Tree FFT <br> 0 0 0 0 0 0 0 0 0 0 <br> <br>
Nonfloating point composite is 0 <br> <br>Floating point composite is 0 <br>Task2-stanford with id=714 iteration:2 has finished. <br> <br> <br> <b> Perm Error in Perm. </b><br>Task2-stanford with id=714 is executing. Iteration:3 <br>
Starting <br> Perm Towers Queens Intmm Mm Puzzle Quick Bubble Tree FFT <br> 0 0 0 0 0 0 0 0 0 0 <br> <br>Nonfloating point composite is 0 <br>
<br>Floating point composite is 0 <br>Task2-stanford with id=714 iteration:3 has finished."<br>-------------------------------------------------------------------------------------------------------------------------------------------------<br>
<br>My question is, why are these errors produced when I enable preemption and are not produced when I disable preemption? Does the fact that this concerns only the recursive functions have to do anything with the problem? Could for some reason, when there is a context switch, the data in the registers of the task being interrupted are not stored correctly in the memory? Or that they are not being correctly transfered back to the registers when it's their turn to be executed again? <br>
<br>Or could it be a memory issue? I have tried initializing the tasks with (RTEMS_MINIMUM_STACK_SIZE * 2) but the errors keep coming. I also tried to allocate more memory to the task stack by using the "CONFIGURE_EXTRA_TASK_STACKS", but when I checked if with the "rtems_stack_checker_report_usage" directive, for some reason it didn't have an impact at the available memory being used by the tasks.<br>
<br>What I need, is for the program to execute with preemption enabled without presenting these errors.<br>What am I missing out? Are there any options I could utilize, or debugging with gdb is the way to continue (I'd like to avoid that if possible)?<br>
<br>Thank you in advance.<br></div><br>
</div><br>
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<br></blockquote></div>