ESP32 Forum • hw timer

Page 1 of 1

hw timer

Posted: Tue Jan 26, 2021 8:35 pm

by debugger3056

Dear colleagues,

I'm not as savvy as everyone else on this forum because of that
Programming MC's is "just" a hobby of mine. That's why I would be
grateful for a useful tip!
I have the following problem:

I initialize a hwTimer with:

Code: [Select all] [Expand/Collapse]

hw_timer_t *timer = NULL;
portMUX_TYPE timerMux = portMUX_INITIALIZER_UNLOCKED;
volatile int interruptCounter;
volatile int totalInterruptCounter;
void IRAM_ATTR onTimer();

GeSHi © Codebox Plus Extension

the Setup

Code: [Select all] [Expand/Collapse]

// Timer
  timer = timerBegin(0, 80, true); // Teiler 80MHz / 80 = 1MHz
  timerLed = timerBegin(1, 800, true); // Teiler 80MHz / 80 = 100kHz
  timerAttachInterrupt(timerLed, &onTimerLed, true);
  timerAlarmWrite(timerLed, 20000, true);
  timerAlarmEnable(timerLed);

GeSHi © Codebox Plus Extension

the interrupt routine

Code: [Select all] [Expand/Collapse]

void IRAM_ATTR onTimer() {
  portENTER_CRITICAL_ISR(&timerMux);
  interruptCounter++;
  totalInterruptCounter++;
  portEXIT_CRITICAL_ISR(&timerMux);
}

GeSHi © Codebox Plus Extension

and the loop

Code: [Select all] [Expand/Collapse]

if (stateCounter == 4) {
    stateCounter = 5;
    LedState = 0;
        
    display.clearDisplay();
    display.setCursor(0,0);
    display.println("measuring... ");
    display.display();
    
    myFile = SD.open(fileString, FILE_WRITE);
    if(!myFile){
      DEBUG_PRINTLN("file dose not exist");
    } else {
      myFile.println(dataString);
    }
    runtime = 0;
    timestamp = 0;
    interruptCounter = 0;
    totalInterruptCounter = 0;
    timerAttachInterrupt(timer, &onTimer, true);
    timerAlarmWrite(timer, 5000, true);
    timerAlarmEnable(timer);
    millisTimer = millis();
    
  } // end of measuring
  // Interrupt completed 25 Jan 2021
  if (interruptCounter > 0) {
    portENTER_CRITICAL(&timerMux);
    int sensorWert = 0;
    timestamp += 0.005;
      
    dataString = String(timestamp, 3) + ","; // drei Dezimalstellen
    // read sensors and append to the string:
    for (byte i = 0; i < AnalogInAnzahl - 1; i++) {
      sensorWert = analogRead(AnalogIn[i]) - AnalogInInit[i];
      dataString += String(sensorWert, DEC) + ",";
    }
    sensorWert = analogRead(AnalogIn[AnalogInAnzahl - 1]) - AnalogInInit[AnalogInAnzahl - 1];
    dataString += String(sensorWert, DEC); // the last data without komma
     
    if (myFile) {
      myFile.println(dataString);
    } else {
      SDerror("error opening filestring");
    }
        
    if (totalInterruptCounter >= 1201) {
      timerAlarmDisable(timer);
      runtime = millis() - millisTimer;
      if (myFile) {
        myFile.close(); 
      }
      DEBUG_PRINT("Messdauer [ms]: ");
      DEBUG_PRINTLN(runtime);
      LedState = 1;
      stateCounter = 6;
    }
    interruptCounter--;
    portEXIT_CRITICAL(&timerMux);
  }

GeSHi © Codebox Plus Extension

if I now fade out in the loop,

Code: [Select all] [Expand/Collapse]

//myFile.println(dataString);

GeSHi © Codebox Plus Extension

I get a runtime of exactly 6000ms.
But if I transfer the data (approx. 40Byte per string) to the SD card
write results in a runtime (different) of approx. 6600ms!
At first I thought the SD routine couldn't do that in 5ms per
Record and tried 10ms, but inaccurate with the same
Result ?
Please please what can be the reason, what do I not understand?

Thanks in advance !!!

Re: hw timer

Posted: Wed Jan 27, 2021 12:47 am

by ESP_Sprite

Your SD-card is a complicated bit of hardware, and any write to it can potentially take a fairly long while as it may need to do things like re-shuffle sector content for wear levelling.

Re: hw timer

Posted: Wed Jan 27, 2021 8:20 am

by debugger3056

Dear,

so how should I save 50Byte per 5ms (without BLE or WLan) ???

Re: hw timer

Posted: Wed Jan 27, 2021 11:03 am

by ESP_Sprite

The easiest way in traditional ESP-IDF would be to use a separate thread for writing, and a big buffer between the two threads to hold any data when writing is slow. Not sure how to solve it in Arduino, I'm afraid.

Re: hw timer

Posted: Wed Jan 27, 2021 2:15 pm

by debugger3056

thank you very much,

could you tell me at last how you would realize a big buffer with ESP-IDF ?

Re: hw timer

Posted: Thu Jan 28, 2021 3:13 am

by ESP_Sprite

The simplest way to do that is to make a large FreeRTOS queue. This can function both to shuttle the data from the sensor reading task to the writing task, as well as as a buffer to smooth out SD-card writing delay times.

Re: hw timer

Posted: Thu Jan 28, 2021 9:12 am

by debugger3056

thank you very much !