Why does'nt this work? (I2C on Bluepill) STM32F103

Projects Programming
1

What you see here is an attempt to debug much bigger program:
I recently moved it to STM32, and ran into this trouble:

In short: the program never sees any packet adressed to it (address 0xB or 11)
I DO see and decode packets incoming on the I2C bus, with a scope connected to SCL1/PB6/22 and SDA1/PB7/23 .
I do NOT get to see them in the serial monitor.

#include <Wire.h>

long lastms;
void receiveEvent(int howMany) {
int x = Wire.read();

Serial.print("U:0x");
Serial.println(x, HEX);
}

void requestEvent() {
    Serial.println("req");
}

void setup() {
  Serial.begin(115200); 

  pinMode(22,INPUT); 
  pinMode(23,INPUT);
  
  Wire.setSCL(22);
  Wire.setSDA(23);
  
  Wire.begin(11);     // join i2c bus as slave
  Wire.onRequest(requestEvent);  // register event
  Wire.onReceive(receiveEvent);  // register event

  lastms = millis();
}

void loop() {
  if (millis() > lastms+1000) {
    Serial.print("=");
    lastms = millis();
  }
}
2

First thought: if receiveEvent and requestEvent are called from an interrupt, does Serial I/O work in an interrupt on the STM32F103?

3

just to make sure, I did:

#include <Wire.h>


long lastms;
int x = 0;

void receiveEvent(int howMany) {
  x = Wire.read();
}

void requestEvent() {
  Serial.println("req");
}

void setup() {
  Serial.begin(115200);

  pinMode(22, INPUT);
  pinMode(23, INPUT);

  Wire.setSCL(22);
  Wire.setSDA(23);

  Wire.begin(11);                // join i2c bus as slave
  Wire.onRequest(requestEvent);  // register event
  Wire.onReceive(receiveEvent);  // register event

  lastms = millis();
}

void loop() {
  if (millis() > lastms + 1000) {
    Serial.print("=");
    lastms = millis();
  }
  if (x != 0) {
    Serial.print("U:0x");
    Serial.println(x, HEX);
    x = 0;
  }
}

It did not help , I still only get "="
Also: please have in mind that the scope is connected to said pins, so the pullups/connection is ok.

4

If requestEvent and receiveEvent are called from an interrupt context, x should be declared volatile otherwise the compiler might optimize away checking it in loop. And the code is still printing from requestEvent.

5

I tried this, it did not help,

#include <Wire.h>
long lastms;
volatile int x = 0;
volatile int y = 0;

void receiveEvent(int howMany) {
  x = Wire.read();
}

void requestEvent() {
  y = 1;
}

void setup() {
  Serial.begin(115200);

  pinMode(22, INPUT);
  pinMode(23, INPUT);

  Wire.setSCL(22);
  Wire.setSDA(23);

  Wire.begin(11);                // join i2c bus as slave
  Wire.onRequest(requestEvent);  // register event
  Wire.onReceive(receiveEvent);  // register event

  lastms = millis();
}

void loop() {
  if (millis() > lastms + 1000) {
    Serial.print("=");
    lastms = millis();
  }
  if (x != 0) {
    Serial.print("U:0x");
    Serial.println(x, HEX);
    x = 0;
  }
  if (y != 0) {
    Serial.println("V");
    y = 0;
  }
}
6

This worked fine for me on my admittedly ancient STM32 core that I haven't updated since forever. I rigged up a Pico to send a message over I2C once every 2 seconds and the Blue Pill displays them.

#include <Wire_slave.h>

volatile char buf[80];
volatile unsigned count = 0;
volatile bool received = false;

void setup() {
   Serial.begin(115200);
   delay(5000);
   Serial.println("Started");

   Wire.begin(11);
   Wire.onReceive(receiveEvent);
}

void loop() {
   if( received ) {
      for( unsigned i=0; i<count; ++i ) {
         Serial.print(buf[i]);
      }
      received = false;
      count = 0;
   }
   delay(50);
}

void receiveEvent(int howMany) {
   for( int i=0; i<howMany; ++i ) {
      char c = Wire.read();
      if( count < sizeof buf ) {
         buf[count++] = c;
      }
   }
   received = true;
}
7

this one is new to me.

8

Remember, it's an ancient core that I'm using. It may no longer be that way.

9

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