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Sampling Rate is going down in Mutitasking

Posted: Wed Nov 13, 2019 3:18 pm
by linearo
Hi everyone,

in a project, I got to send sensor data over WiFi while i scan the Sensor with 10kHz simultaneously.
If I scan first an send afterwards, i get sampling rates up to 90kHz. But if I separate the Read and Send tasks on Core 0 and 1 so I can scan "forever" without running out of storage, I just get a maximum sampling rate of 950Hz.

There is another article on this topic here: viewtopic.php?f=19&t=10084&p=41613
but unfortunately it has no answers.

Here is my Code:

Code: Select all

#include <Arduino.h>                      //Declaration of extern libraries
#include <CircularBuffer.h>
#include <WiFi.h>

CircularBuffer <uint8_t, 4096*10> Buffer;    //Buffer Declaration of Type uint8_t and size of 1024 places
TaskHandle_t WriteInBuffer;               //Declaration of separate tasks to run on Core 0 and 1
TaskHandle_t ReadFromBuffer;

int analogPin = 32;                       //Declaration of Pin where analog Data is read

const char *ssid = "ESP32ap";             //set WiFi settings
const char *password = "12345678";
WiFiServer wifiServer(80);                //WiFi Server on Port 80

uint8_t value = 0;                        // = value from ADC before Buffer
uint8_t element = 0;                      // = value from ADC after Buffer
int packSize = 4096;                       // = number of Data Points send in 1 Package
int nPacks = 4;                           // = number of Packs send after each other
bool connect = false;                     // = variable neccesary to communicate between Tasks

void WriteIn(void * pvParameters){        //Task to write in buffer
  for(;;){                                //never ending loop
    if (connect == true){                 //read analog value as long as the client is connected
      value = analogRead(analogPin);
      Buffer.unshift(value);              //write at the beginning of the buffer --> [here,3,2,1]
      vTaskDelay(5);                          //neccesary to not trigger the WatchDog

void ReadFrom( void * pvParameters){              //Task to Read from Buffer and Send over WiFi
  for(;;){                                        //never ending loop
    WiFiClient client = wifiServer.available();   //Declaration of client 

    if (client){                                  //if client is connected
      int Bytes = 0;                              // = Bytes send in this session
      int i = 0;                                  // = counter for loop
      connect = true;                             //let other Task know that client is connected
      Serial.println("Client connected");
      while(client.connected()){                  //Maybe this loop is not neccesary?
        while(i < nPacks){                        //while not all Packs are sent
          //Serial.println(Buffer.size());          // this command is neccesary in a strange way
          if(Buffer.size() >= packSize){          //if Buffer is bigger than the Pack size, send a Pack
            for (int j = 0; j < packSize; j++){
              element = Buffer.pop();             //get entry fom Buffers end [4,3,2,1(here)] --> FIFO principle
              Bytes += client.write(element);     //send elements over WiFi
            i ++;                                 //increment the Packs Loop after sending a Pack
        client.stop();                            //Disconnect Client after sending all Data 
        connect = false;                          //let other Task know about it
        Serial.println("Client disconnected");
        Serial.print("Bytes sent: ");
        Serial.println(Bytes);                    //number of Bytes sent
      connect = false;
    vTaskDelay(10);                               //neccesary to not trigger the WatchDog

void setup() {
  Serial.begin(9600);                   //Configuring Serial Monitor
  Serial.println("Configuring access point...");  
  WiFi.softAP(ssid, password);          //opening Access Point

  IPAddress myIP = WiFi.softAPIP();
  Serial.print("AP IP address: ");
  Serial.println(myIP);                 //Print IP-Adress of ESP
  wifiServer.begin();                   //Start WiFi Server

                  WriteIn,              /* Task function. */
                  "WriteInBuffer",      /* name of task. */
                  10000,                /* Stack size of task */
                  NULL,                 /* parameter of the task */
                  1,                    /* priority of the task */
                  &WriteInBuffer,       /* Task handle to keep track of created task */

                  ReadFrom,             /* Task function. */
                  "ReadFromBuffer",     /* name of task. */
                  10000,                /* Stack size of task */
                  NULL,                 /* parameter of the task */
                  1,                    /* priority of the task */
                  &ReadFromBuffer,      /* Task handle to keep track of created task */

void loop() {

Thanks in advance!