Failed to detect MPU9250 using I2C

[csabakeszegh]

First, thank you for this great project. I'd like to connect to an MPU9250 using I2C to my NodeMCU clone. As the first step, I wrote a custom command i to enumerate I2C devices. I'm calling the following method:

#include "i2c_master.h"
int ICACHE_FLASH_ATTR scan_i2c(char *buf)
{
    int i = 0;
    int found = 0;
    i2c_master_gpio_init();
    for (i=1; i<127; i++) {
        i2c_master_start();
        i2c_master_writeByte(i<<1);
        if (i2c_master_checkAck()) {
            ++found;
        }   
        i2c_master_stop();
     }   
    ets_sprintf(buf, "Found i2c devices: %d", found);
}

The probIem that I always get 0 devices. The connection should be okay, because when I upload a sketch using Arduino IDE for Esp8266, utilizing the Wire library, it works and receive ACK for 0x68. I also tried a logic analyzer to track down the problem.

When using Wire library it works:

When using i2c_master code I get NAK:

The difference I see that Wire is ~2x faster. (I tried to change the delays in i2c_master_wait, it became faster, but still got NAK.)

The MPU9250 device works well with an Arduino Nano (and also from the NodeMCU using the Wire library).

I tried to connect a Nano as I2C slave, and the enumeration worked with i2c_master code. Any help or hint is really appreciated.

[cnlohr]

I... uhhh... I don't know what master_i2c.h is. I've only used static_i2c.h. https://github.com/cnlohr/esplocalizer/blob/master/firmware-c/user/static_i2c.h

That said your trace looks good, so it's probably with your library. You could try mine?

Just

#define I2CSPEEDBASE 1
#define I2CNEEDGETBYTE
#define DSDA 5
#define DSCL 4

#include "static_i2c.h"

Then in your code

ConfigI2C(); //Do this once...

    SendStart();
    r = SendByte( MPU_ADDY );
    if( r ) { SendStop(); printf("Fault\n"); return -3; }
    SendByte( ... ); //Do stuff
    SendByte( ... ); //Do other stuff. 
    SendStop();

[csabakeszegh]

Thanks for the quick response. i2c_master is a software bit-banging I2C library in the NonOS SDK. By default it uses GPIO2 (SDA), and GPIO14 (SCL) pins. Changing them to GPIO4, GPIO5 respectively solved my problem. I'm not sure why. Maybe interfere with UART?