ESP32 Forum

Posted: **Thu Oct 03, 2024 4:01 am**

Hi.
I am sending a stable signal with a frequency of 10000 Hz from a quartz oscillator. The variable M must be stable and in the range from M=240013970 - 240013971.But the variable M varies over a larger range. I think other interrupts may have a higher priority and calling my interrupt is waiting for the other interrupts to end. Please help me.

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const    int      interruptPin = 27; // GPIO pin where the interrupt will be configured               //
         bool     start_gate=1;                                                                       //
         uint32_t tik_new,tik_old;                                                                    //
         uint64_t tik,tik_start;                                                                      //
         uint64_t time_new,time_old;                                                                  //
         uint64_t N_int;                                                                              //
volatile uint64_t N=0,M=0;                                                                            //
//----------------------------------------------------------------------------------------------------//
void IRAM_ATTR buttonTick()                                                                           //
{                                                                                                     //
   tik_new = esp_cpu_get_cycle_count();                                                               //
   tik     = tik+tik_new-tik_old;                                                                     //
   if (tik_new<tik_old) tik=tik+4294967296;                                                           //
   tik_old=tik_new;                                                                                   //
   N_int=N_int+1;                                                                                     //
   if (start_gate==1            )  {tik_start=tik;N_int=0;start_gate=0;  }                            //
   if ((tik-tik_start)>=240000000) {N=N_int;M=tik-tik_start;start_gate=1;}                            //
}                                                                                                     //
//----------------------------------------------------------------------------------------------------//
void setup()                                                                                          //
{                                                                                                     //
  Serial.begin(115200);                                                                               //
  pinMode(interruptPin, INPUT); // Configure the pin as an input with an internal pull-up resistor    //
  attachInterrupt(interruptPin, buttonTick, RISING); // Configure the interrup                        //
}                                                                                                     //
//----------------------------------------------------------------------------------------------------//
void loop()                                                                                           //
{                                                                                                     //
  time_new = esp_timer_get_time();                                                                    //
  if ((time_new-time_old)>=1000000)                                                                   //
  {                                                                                                   //
   Serial.print(" N= ");Serial.print(N);Serial.print(" M= ");Serial.println(M);                       //
   time_old=time_new;                                                                                 //
  }                                                                                                   //
}                                                                                                     //

GeSHi © Codebox Plus Extension

N= 10001 M= 240013929
N= 10001 M= 240013875
N= 10001 M= 240013848
N= 10001 M= 240014067
N= 10001 M= 240014070
N= 10001 M= 240014229
N= 10001 M= 240014145
N= 10001 M= 240013806
N= 10001 M= 240013839
N= 10001 M= 240014007
N= 10001 M= 240013806
N= 10001 M= 240014157

Posted: **Thu Oct 03, 2024 7:42 am**

Either that, or cache hits/misses, or writes to the AHB bus that take a few cycles, or...

Suggest you use a peripheral (RMT or MCPWM, for example) if you need to measure the time precisely.

Posted: **Thu Oct 03, 2024 8:29 am**

I didn't understand what I needed to do "Suggest you use a peripheral (RMT or MCPWM, for example) if you need to measure the time precisely"?
There is an assumption that the interrupt on pin 27 has a low interrupt priority. And if another interrupt has a higher priority, then the interrupt with a higher priority is executed first, and the interrupt on pin 27 waits for the end of this high-level interrupt.
Question:
1.How do I set a higher interrupt level for the interrupt on pin 27?
2. Is it possible to disable other high-level interrupts and leave the interrupt only on pin 27?
Please provide an example from the help file or correct this code. Or give a link to a similar example.

Posted: **Thu Oct 03, 2024 9:57 am**

I'm saying that trying to get jitterless interrupt is a fools errand: aside from higher-level interrupts, there's a fair few other things that will affect timing, and you cannot influence those as they are fundamental to the system. Instead, use a peripheral (which is not affected by interrupt jitter) to take the measurements you need.

Posted: **Thu Oct 03, 2024 12:18 pm**

And if you use not pin 27 to call an interrupt, but another pin that has a higher priority?
Which pin input can have a higher priority?

Posted: **Thu Oct 03, 2024 1:37 pm**

Buldakov wrote: ↑
Thu Oct 03, 2024 12:18 pm
And if you use not pin 27 to call an interrupt, but another pin that has a higher priority?
Which pin input can have a higher priority?

Please read what I wrote. Even if you were able to manage to snag a higher priority interrupt (which is independent from the GPIO you use, by the way) you would not solve the issue.

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