The real-time performance of nuttx

[fft]

Hi team:


I've been puzzled by a strange problem for a long time, when i  use FOC motor 
control. It seems that the FOC control thread failed to be scheduled in real 
time. The code structure of ./apps/examples/foc/foc_float_thr.c can be 
simplified description is as follows:



  while (motor.mq.quit == false)
    {
            ...FOC 
control code...


          /* Get FOC device state 
*/
          ret = 
foc_dev_state_get(&dev);
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if (ret < 0)
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; {
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
PRINTF("ERROR: foc_dev_state_get failed %d!\n", ret);
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
goto errout;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; }


&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ...FOC 
control code...

&nbsp;&nbsp;&nbsp; }



where foc_dev_state_get will be periodic blocked by waiting semaphore, and ADC 
interrupt periodic give semaphore.
My custom board is based on stm32f405 and my config about foc as shown below:


CONFIG_EXAMPLE_FOC_PWM_FREQ=20000
CONFIG_EXAMPLE_FOC_NOTIFIER_FREQ=10000
CONFIG_EXAMPLE_FOC_CONTROL_PRIO=255


So, the FOC control code will be executed every 100us theoretically, In fact, 
this is true in most cases tested on real hardware, but there's 
sporadic unexpected states, that the execution interval between two FOC control 
is 120~170us, There's no effect when the motor speed is low, but when the motor 
speed is very high(up to 60000 erpm), this will cause serious problem, the 
motor may suddenly get stuck and burn. What puzzles me is the priority of FOC 
control thread already been set to the highest 255, and i have enabled the 
CONFIG_PRIORITY_INHERITANCE, why the FOC control threads was delayed so serious 
? BTW, ther execution time of single FOC control loop is 60~70us, and there's 5 
custom task in my case:



Is my configuration incorrect or the real-time performance of nuttx can not 
meet the requirements?
Does anyone else have the same problem?


Best regard
Zou