TM4C123GH6PM: I2C Communication not working on intial power up but works once debugged.

Yashwanth Gandeti

Part Number: TM4C123GH6PM

Hi,

I2C is not reading registers on intial power up, but if i debugged once then its working as expected in all the next runs.

I'm using CCSv8.1, Windows 10, EK - TM4C123GXL

I2C0 Channel I'm using for I2C Communication.

I2C0 SCL - PB2

I2C0 SDA - PB3

Here i attached my code snippets:

     /* Check that I2C SDA is not being held low If so, toggle I2C SCL until it is released
      * Safe for i2c Communication  when Reset button is pressed  */

    GPIOPinTypeGPIOInput(GPIO_PORTB_BASE, GPIO_PIN_3);
    GPIOPinTypeGPIOOutput(GPIO_PORTB_BASE, GPIO_PIN_2);
    while (GPIOPinRead(GPIO_PORTB_BASE, GPIO_PIN_3) != GPIO_PIN_3)
    {
        GPIOPinWrite(GPIO_PORTB_BASE, GPIO_PIN_2, 0);
        GPIOPinWrite(GPIO_PORTB_BASE, GPIO_PIN_2, GPIO_PIN_2);
    }

Initializing I2c:

/* I2C0 Init */
    /* Enable the peripheral */
    SysCtlPeripheralEnable (SYSCTL_PERIPH_I2C0);

    // Configure the GPIO Pin Mux for PB2 for I2C0SCL

    GPIOPinConfigure(GPIO_PB2_I2C0SCL);
    GPIOPinTypeI2CSCL(GPIO_PORTB_BASE, GPIO_PIN_2);

    // Configure the GPIO Pin Mux for PB3 for I2C0SDA

    GPIOPinConfigure(GPIO_PB3_I2C0SDA);
    GPIOPinTypeI2C(GPIO_PORTB_BASE, GPIO_PIN_3);

I'm using TI-RTOS 2.16.00.08 for my project configured below function as Task to get the data from IMU Sensor:

void get_imu()
{
    I2C_Handle i2c;
    I2C_Params i2cParams;
    uint8_t pwr;
    pwr = 0x00;

    //Create I2C for usage
    I2C_Params_init(&i2cParams);
    i2cParams.bitRate = I2C_400kHz;
    i2c = I2C_open(IMU_SENSOR, &i2cParams);
    if (i2c == NULL)
    {
        System_abort("Error Initializing I2C\n");
    }
    else
    {
        System_printf("I2C Initialized!\n");
    }

    // Initialize the MPU6050
    writeRegister(i2c, 0x6B, 0x80, true);
    readRegister(i2c, 0x6B, &pwr, 1, true);
    do
    {
        readRegister(i2c, 0x6B, &pwr, 1, true);
    }
    while (pwr & 0x40 != 0x40);

    // Use PLL with X axis gyroscope reference
    writeRegister(i2c, 0x6B, 0x01, true);
    // Enable I2C Master mode
    writeRegister(i2c, 0x6A, 0x20, true);
    // Set sample rate divider
    writeRegister(i2c, 0x19, 0x13, true);
    writeRegister(i2c, 0x67, 0x11, true);

    while (1)
    {
        Semaphore_pend(IMUSem, BIOS_WAIT_FOREVER);
        readRegister(i2c, 0x3B, (uint8_t *) &signal.imu.mpu6050, 14, true);
    }

    //Deinitialized I2C
    I2C_close(i2c);
    System_printf("I2C closed!\n");
    System_flush();
}

Regards,

Yashwanth Kumar Gandeti.

over 6 years ago

0 Bob Crosby over 6 years ago

TI__Guru 72500 points

What you posted looks correct to me. I suggest you use a logic analyzer to look at SCL and SDA without Code Composer being connected. (Use the RESET button.

0 Yashwanth Gandeti over 6 years ago in reply to Bob Crosby

Intellectual 595 points

Hi Bob Crosby,

I verified with logic analyzer. Here is the screen shot of the same. Its reading 00 from all.

After debugging only once by keeping break point at

  writeRegister(i2c, 0x6B, 0x80, true); // in get_imu() task

and ran the code its getting proper sensor data even after reset. Here is the screen shot after debugging once and pressed the button as you suggested.

sorry I didn't find any change by using logic analyzer too.

Regards,

Yashwanth Kumar Gandeti.

0 Bob Crosby over 6 years ago in reply to Yashwanth Gandeti

TI__Guru 72500 points

What you need is the logic analyzer trace of the beginning when it is in the failing mode. The write of 0x80 to register 0x6B, followed by the reading of that register until the sleep bit is set (0x40) and then the writing of 0x01. The write of 0x01 clears the sleep bit allowing the MPU6050 to start working.

0 Yashwanth Gandeti over 6 years ago in reply to Bob Crosby

Intellectual 595 points

Hi Bob Crosby,

Hope now attached proper image , In that you can see that 0x6B is wrote with 0x01(6th record in the payload).

Later output of the 14 registers from 0x3B is 00. Here is the screen shot of the same.

Please help me in this.

Regards,

Yashwanth Kumar Gandeti.

0 Bob Crosby over 6 years ago in reply to Yashwanth Gandeti

TI__Guru 72500 points

I see the problem. You write 0x80, then you read a 0x00 twice. It should continue reading until you read a 0x40. It is writing the 0x01 too soon. The MPU6050 has not finished its reset sequence. The root cause is operator precedence in your do {} while;. Try this:

    do
    {
        readRegister(i2c, 0x6B, &pwr, 1, true);
    }
    while ((pwr & 0x40) != 0x40);

0 Yashwanth Gandeti over 6 years ago in reply to Bob Crosby

Intellectual 595 points

Bob Crosby,
Thanks for your support. Your solution resolved my issue.

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TM4C123GH6PM: I2C Communication not working on intial power up but works once debugged.