Problem with Adafruit library and I2c display

Mbed OS
1

Hello,
In the past i have used some i2c based displays(ssd1306 driver) with my Nucleo F303K8. but when i tried to make a little project the other day, i discovered that there’s something wrong with my code. When using the following code:

#include "mbed.h"
#include "Adafruit_SSD1306.h"
 
DigitalOut myled(LED1);
 
 
// an I2C sub-class that provides a constructed default
class I2CPreInit : public I2C
{
public:
    I2CPreInit(PinName sda, PinName scl) : I2C(sda, scl)
    {
        frequency(400000);
        start();
    };
};
 
 
I2CPreInit gI2C(D4,D5);
Adafruit_SSD1306_I2c scherm(gI2C,D13);
 

int main()
{   
int x = 0;
scherm.clearDisplay();
    
    while(1)
    {
        myled = !myled;
        scherm.printf("%d\r",x);
        scherm.display();
        x++;
        wait(1.0);
    }
}

Everything works fine,
But when i rewrite the code so that the display is ‘controlled’ by a void outside of the main it suddenly doesn’t work anymore. The rewritten code:

#include "mbed.h"
#include "Adafruit_SSD1306.h"
 
Ticker plussen;
DigitalOut led(LED1);

// an I2C sub-class that provides a constructed default
class I2CPreInit : public I2C
{
public:
    I2CPreInit(PinName sda, PinName scl) : I2C(sda, scl)
    {
        frequency(400000);
        start();
    };
};
 
 
I2CPreInit gI2C(D4,D5);
Adafruit_SSD1306_I2c scherm(gI2C,D13);
 int x;
 void plus(){
        x++;
        scherm.clearDisplay();
        scherm.setTextCursor(1,1);
        scherm.printf("%d", x);
        scherm.display();
        }
        
 
int main()
{   
scherm.clearDisplay();
plussen.attach(&plus, 1);
    while(true){
            led = !led;
            wait_ms(500);
            }
}

As far as i could test with my knowledge of programming there is something wrong with the .display(); With timers i discovered that it takes about 2 minutes to pass the display(); funtion. When lowering the frequency it also takes longer to pass the .display(); and when the frequency is higher it is a little faster. I also checked if it isn’t a hardware probleme by using other microcontrollers and other displays but the results stay the same. So am i using the library wrong wich creates this fault or is it because of something which isn’t my fault. I hope to hear from you,
Wouter de Gries

2

Hello,

you are right the method display() freeze the code in the interrupt. I do not know why, but I am sure, it is not because of you call it in a void, out of the main. Probably that is about you call it in the interrupt context.

Anyway, placing printf or any other methods what can be blocking or slow into interrupt, is not good practice.

volatile bool dothis = false;
void plus(){
    dothis = true;
}

 void test(int x){
        scherm.clearDisplay();
        scherm.setTextCursor(1,1);
        scherm.printf("%d", x);
        scherm.display();
}
        
 
int main(){   
    printf("Run\n");
    int x;
    Timer timer;
    timer.start();
    plussen.attach(&plus, 1);
    timer.start();

    while(true){
        if (timer.read_ms() > 1000){
            led = !led;
            timer.reset();
        }
        if(dothis){
            test(x++);
            dothis = false;
        }
    }
}

Usually is good to share links to examples, libraries and info about Mbed OS version what you use.

BR, Jan