• STM32 HAL documentation
• Wiki STM32

I want to make the i2c transactions as fast as possible, and I am using STM32. The first part is to emulate a i2C device, and then optimize it.

Simulate a i2C sensor with Arduino

The arduino code is:

#include <Wire.h>

void setup() {
  Wire.begin(8);                // join i2c bus with address #8
  Wire.onRequest(requestEvent); // register event
}

void loop() {
  delay(100);
}

// function that executes whenever data is requested by master
// this function is registered as an event, see setup()
void requestEvent() {
  Wire.write("hello "); // respond with message of 6 bytes
  // as expected by master
}

The example receiver would be:

#include <Arduino.h>

#include <Wire.h>

// Logic analyser
#define LA_CH0 D3
#define LA_CH1 D2

void setup() {
  Wire.setSDA(PC9);
  Wire.setSCL(PA8);
  Wire.setClock(100000); // 100KHz Normal mode
  Wire.begin();        // join i2c bus (address optional for master)
  Serial.begin(9600);  // start serial for output

  pinMode(LA_CH0, OUTPUT);
  pinMode(LA_CH1, OUTPUT);
}

void loop() {
  digitalWrite(LA_CH0, HIGH);
  Wire.requestFrom(8, 6);    // request 6 bytes from peripheral device #8
  digitalWrite(LA_CH0, LOW);

  digitalWrite(LA_CH1, HIGH);
  while (Wire.available()) { // peripheral may send less than requested
    char c = Wire.read(); // receive a byte as character
    Serial.print(c);         // print the character
  }
  digitalWrite(LA_CH1, LOW);


  delay(10);
}

And the timming analysis of this one is the next:

That is 600 us for requesting, and 10uS for receiving.

—

Arduino code:

#include <Wire.h>

void setup()
{
  Wire.begin(); // join i2c bus (address optional for master)
}


void loop()
{
  Wire.beginTransmission(0); // transmit to device #4
  Wire.write("hello!");        // sends five bytes
  Wire.endTransmission();    // stop transmitting

  delay(500);
}

I am not able to make it work, but I think is because I am not understanding who is master and slave, and the arduino libraries are not helping.