Once that is working, make the few changes needed to get it running on a pair of ESP32's. Once that is running, now carefully and slowly modify (Leave old code in, just // comment out) the code to do what you want.

I am currently trying to implement an SPI communication between 2 ESP32 using arduino IDE but i am facing a problem.

I set 1 as a master using the normal SPI library and the second one as slave using ESP32SPISlave.

Master SW is basically writing 0 or 1 to slave device and wait for a response

if the master send a 0 the slave will send back 2 in the next communication, 

if the master send 1 the slave will send back 1 in the next communication.

the problem that sometimes even if the master send 1 i receive the number 2 instead of 1 so it seems that it doesn't override the previous value.

I am not sure exactly what's the problem. could you please support me?

I will paste both SW

You can find the picture of the issue in the link below

https://drive.google.com/file/d/1K08ntvOcR7fH9SyWb-RZu7XXCOKP2msH/view?usp=sharing

Master SW

#include <SPI.h>

// Define ALTERNATE_PINS to use non-standard GPIO pins for SPI bus

#ifdef ALTERNATE_PINS
  #define VSPI_MISO   26
  #define VSPI_MOSI   27
  #define VSPI_SCLK   25
  #define VSPI_SS     32
#else
  #define VSPI_MISO   MISO
  #define VSPI_MOSI   MOSI
  #define VSPI_SCLK   SCK
  #define VSPI_SS     SS
#endif

static const int spiClk = 1000000; // 1 MHz

int data1;

//uninitalised pointers to SPI objects
SPIClass * vspi = NULL;

void setup() {
  Serial.begin(115200);
    delay(2000);
  //initialise instance of the SPIClass attached to HSPI
  vspi = new SPIClass(VSPI);
  
  //clock miso mosi ss
#ifndef ALTERNATE_PINS
  //initialise hspi with default pins
  //SCLK = 14, MISO = 12, MOSI = 13, SS = 15
  vspi->begin();
#else
  //alternatively route through GPIO pins
  vspi->begin(VSPI_SCLK, VSPI_MISO, VSPI_MOSI, VSPI_SS); //SCLK, MISO, MOSI, SS
#endif

  //set up slave select pins as outputs as the Arduino API
  //doesn't handle automatically pulling SS low
  pinMode(VSPI_SS, OUTPUT); //HSPI SS
}

// the loop function runs over and over again until power down or reset
void loop() {
  vspi_send_command();
  delay(1000);
}

void vspi_send_command() {
  byte data_on = 0b00000001; // data 1 to turn on LED of slave
  byte data_off = 0b0000000; // data 0 to turn off LED of slave
  
  vspi->beginTransaction(SPISettings(spiClk, MSBFIRST, SPI_MODE0));
  digitalWrite(VSPI_SS, LOW);
  data1 = vspi->transfer(data_on);
  digitalWrite(VSPI_SS, HIGH);
  vspi->endTransaction();
  Serial.print("data sent is 1 and data received is ");
  Serial.println(data1);
  delay(1000);
  
  vspi->beginTransaction(SPISettings(spiClk, MSBFIRST, SPI_MODE0));
  digitalWrite(VSPI_SS, LOW);
  data1 = vspi->transfer(data_off);
  digitalWrite(VSPI_SS, HIGH);
  vspi->endTransaction();
  Serial.print("data sent is 0 and data received is ");
  Serial.println(data1);
  delay(1000);

}

Slave SW

#include <ESP32SPISlave.h>

ESP32SPISlave slave;

static constexpr uint32_t BUFFER_SIZE {32};
uint8_t spi_slave_tx_buf;
uint8_t spi_slave_rx_buf;

#define LED 2
void setup() {
    Serial.begin(115200);
    delay(2000);
    pinMode(LED, OUTPUT);
    // begin() after setting
    // HSPI = CS: 15, CLK: 14, MOSI: 13, MISO: 12 -> default
    // VSPI = CS:  5, CLK: 18, MOSI: 23, MISO: 19
    slave.setDataMode(SPI_MODE0);
    //slave.begin();
    slave.begin(VSPI);   // you can use VSPI like this

    // clear buffers
    memset(spi_slave_tx_buf, 0, BUFFER_SIZE);
    memset(spi_slave_rx_buf, 0, BUFFER_SIZE);
}

void loop() {
    // block until the transaction comes from master
    slave.wait(spi_slave_rx_buf, spi_slave_tx_buf, BUFFER_SIZE);

    // if transaction has completed from master,
    // available() returns size of results of transaction,
    // and buffer is automatically updated
    char data;
    while (slave.available()) {
        // show received data
         Serial.print("Command Received: ");
         Serial.println(spi_slave_rx_buf);
         data = spi_slave_rx_buf;
         slave.pop();
    }
    if(data == 1 )
    {
        Serial.println("Setting LED active HIGH ");
        digitalWrite(LED, HIGH);
        memset(spi_slave_tx_buf, 1, BUFFER_SIZE);
    }
    else if(data == 0 )
    {
        Serial.println("Setting LED active LOW ");
        digitalWrite(LED, LOW);
        memset(spi_slave_tx_buf, 2, BUFFER_SIZE);
    }
     Serial.println("");
}

Thank you again for your cooperation.