I am providing this cpu utilization technique to the community courtesy of a brilliant and kind engineer in Texas, Jimmie Curry. Thanks Jimmie!
In the MQX idle task (idletask.c) we find:
The idle task is of the lowest priority and is preempted by any active task and ISRs.
while (1) {
#if !defined(MQX_ENABLE_IDLE_LOOP) || MQX_ENABLE_IDLE_LOOP
if (++kernel_data->IDLE_LOOP.IDLE_LOOP1 == 0) {
if (++kernel_data->IDLE_LOOP.IDLE_LOOP2 == 0) {
if (++kernel_data->IDLE_LOOP.IDLE_LOOP3 == 0) {
++kernel_data->IDLE_LOOP.IDLE_LOOP4;
} /* Endif */
} /* Endif */
} /* Endif */
#endif
The highlighted code consist of 5 assembly language instructions, each of which requires one core clock cycle. (ARM Cortex M4)
Each IDLE_LOOP counter is a 32 bits, which together becomes a 128 bit counter.
In my case, the core clock is 120 MHz
Count_Time = 1/120e6 * 5 (the time to complete one count)
Count_Time * 2^32 is required to roll over, in my case approximately 3 minutes.
Thus if I set a break point on the second if statement and only the idle task were running, three minutes would elapse between breaks.
That means that if we measure 6 minutes of operation between breaks, we have 50% CPU utilization by the OS/Application code.
10 minutes between breaks, indicates 70% OS/Application utilization.
