I'm developing a CPU usage monitor on a ADuC7126 using RTX that will later be incorporated into other projects but have ran into a subtle issue that I hope someone can shed some light into.
The mechanism is to use a recurring 1 second timer inside a task to calculate the CPU usage and a incremental counter in os_idle_demon(). Since this project has only 2 tasks running, tskCpuUsageCalc and os_idle_demon, I would assume the counter would have the same ballpark value each time the timer expires since it's idling consistently but it's not. Most of the time the counter value is ~125000 but occasionally (1 out of ~5) it would be ~250000 and very rarely it would be ~375000. It seems like it's always 1X, 2X, or 3X. I tried to define the counter variable as volatile to prevent caching but the result is still the same.
Here is the snippit in RTX_Conf_ADuC712x.c:
extern OS_TID tidCpuUsageCalc; extern volatile U32 cpuIdleCnt; ... __task void os_idle_demon (void) { for (;;) { /* HERE: include optional user code to be executed when no task runs.*/ cpuIdleCnt++; } } void os_tmr_call (U16 info) { switch (info) { case TMR_1_SECOND: isr_evt_set(EVT_TMSTMP_PROC, tidCpuUsageCalc); break; } }
Here is the snippit in main.c:
volatile U32 cpuIdleCnt = 0; int cpuUsage = 0; ... __task void tskCpuUsageCalc(void) { // Create a 1sec timer oidTmr1sec = os_tmr_create (100, TMR_1_SECOND); while (1) { os_evt_wait_or(EVT_TMSTMP_PROC, 0xFFFF); // Calculate CPU usage cpuUsage = 100 - ((cpuIdleCnt * 100) / MAX_IDLE_CNT); // Initialize cpuIdleCnt before starting the timer again cpuIdleCnt = 0; // Recreate 1sec timer when it expires since RTX only has 1-shot timers oidTmr1sec = os_tmr_create (100, TMR_1_SECOND); } } __task void init_task(void) { tidCpuUsageCalc = os_tsk_create_user(tskCpuUsageCalc, 50, &CpuUsage_stack, sizeof(CpuUsage_stack)); os_tsk_delete_self(); } int main (void) { os_sys_init(init_task); /* Initialize RTX */ }
Any advice would be appreciated.