Dear ST community,
I am running stm32f4-7 with FreeRTOS, and lwip, I am running TCP server by use of LWIP and some other application logic.
I need to generate PPM signal (8 PWM pulses with different length) every 20ms. For this purpose I am using timer10, and on each interrupt I set one GPIO pin to 1 or 0. Each PWM pulse is from 0,5ms to 1,1ms, so the timming i gues is not that fast... I am running system clock of 168MHz.
everything runs fine, just sometimes, PPM signal has some parts longer than it should be, most porbably timer interrupt is called with some delay. I suggest processor is bussy with some other task, thus cannot service interrupt for the timer. I have nested interrupts enabled with the priority for my timer = 0.
I was trying to debug this by SWV. where I can see entering and exiting of interrupts.
my question fot the SWV:
- What does the overflow means in the sequence list of exceptions?
- The message with index 55403 says I am entering TIM10 interrupt, but then I see index 55409 USART1_IRQ, however usart has lower priority than time10, so does this mean usart is preepting handling of tim10?
- index 55403 and 55417 I can see just tim10 entering, but no exit, why does it happen? most of the tiem I can see entering of tim10 interrupt and then exit of tim10 interrupt
I know RTOS has probably heigher interrupt priority then timers do, so maybe when there is a flag raised for tim10 interrupt, it cannot be handled becouse RTOS is bussy with CPU, but I am delayed with interrupt routine for timer 10 for more then 0,1ms, which I thing is too much to be delayed even if RTOS is doing something. Or is it something that is normal?
Q2: Is there some other way to generate PPM signal?
Thank You.
Peter
