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I have a problem with an I2C bus on a STM32F4, that get locked pretty fast after startup. The SDA line get hold low the whole time and the SCL line high. So this looks like a standard I2C bus lock to me and I tried the following routine to unlock it after the I2C transmit throws a BUSY error:

void I2C3_ClearBusyFlagErratum(I2C_HandleTypeDef *instance)
{
    GPIO_InitTypeDef GPIO_InitStruct;
    int timeout =100;
    int timeout_cnt=0;

    // 1. Clear PE bit.
    instance->Instance->CR1 &= ~(0x0001);

    //  2. Configure the SCL and SDA I/Os as General Purpose Output Open-Drain, High level (Write 1 to GPIOx_ODR).
    GPIO_InitStruct.Mode         = GPIO_MODE_OUTPUT_OD;
    GPIO_InitStruct.Alternate    = GPIO_AF4_I2C3;
    GPIO_InitStruct.Pull         = GPIO_PULLUP;
    GPIO_InitStruct.Speed        = GPIO_SPEED_FREQ_HIGH;

    GPIO_InitStruct.Pin          = I2C3_SCL_PIN;
    HAL_GPIO_Init(I2C3_SCL_PORT, &GPIO_InitStruct);
    HAL_GPIO_WritePin(I2C3_SCL_PORT, I2C3_SCL_PIN, GPIO_PIN_SET);

    GPIO_InitStruct.Pin          = I2C3_SDA_PIN;
    HAL_GPIO_Init(I2C3_SDA_PORT, &GPIO_InitStruct);
    HAL_GPIO_WritePin(I2C3_SDA_PORT, I2C3_SDA_PIN, GPIO_PIN_SET);


    // 3. Check SCL and SDA High level in GPIOx_IDR.
    while (GPIO_PIN_SET != HAL_GPIO_ReadPin(I2C3_SCL_PORT, I2C3_SCL_PIN))
    {
        timeout_cnt++;
        if(timeout_cnt>timeout)
            return;
    }

    while (GPIO_PIN_SET != HAL_GPIO_ReadPin(I2C3_SDA_PORT, I2C3_SDA_PIN))
    {
        timeout_cnt++;
        if(timeout_cnt>timeout)
            return;
    }

    // 4. Configure the SDA I/O as General Purpose Output Open-Drain, Low level (Write 0 to GPIOx_ODR).
    HAL_GPIO_WritePin(I2C3_SDA_PORT, I2C3_SDA_PIN, GPIO_PIN_RESET);

    //  5. Check SDA Low level in GPIOx_IDR.
    while (GPIO_PIN_RESET != HAL_GPIO_ReadPin(I2C3_SDA_PORT, I2C3_SDA_PIN))
    {
        timeout_cnt++;
        if(timeout_cnt>timeout)
            return;
    }

    // 6. Configure the SCL I/O as General Purpose Output Open-Drain, Low level (Write 0 to GPIOx_ODR).
    HAL_GPIO_WritePin(I2C3_SCL_PORT, I2C3_SCL_PIN, GPIO_PIN_RESET);

    //  7. Check SCL Low level in GPIOx_IDR.
    while (GPIO_PIN_RESET != HAL_GPIO_ReadPin(I2C3_SCL_PORT, I2C3_SCL_PIN))
    {
        timeout_cnt++;
        if(timeout_cnt>timeout)
            return;
    }

    // 8. Configure the SCL I/O as General Purpose Output Open-Drain, High level (Write 1 to GPIOx_ODR).
    HAL_GPIO_WritePin(I2C3_SCL_PORT, I2C3_SCL_PIN, GPIO_PIN_SET);

    // 9. Check SCL High level in GPIOx_IDR.
    while (GPIO_PIN_SET != HAL_GPIO_ReadPin(I2C3_SCL_PORT, I2C3_SCL_PIN))
    {
        timeout_cnt++;
        if(timeout_cnt>timeout)
            return;
    }

    // 10. Configure the SDA I/O as General Purpose Output Open-Drain , High level (Write 1 to GPIOx_ODR).
    HAL_GPIO_WritePin(I2C3_SDA_PORT, I2C3_SDA_PIN, GPIO_PIN_SET);

    // 11. Check SDA High level in GPIOx_IDR.
    while (GPIO_PIN_SET != HAL_GPIO_ReadPin(I2C3_SDA_PORT, I2C3_SDA_PIN))
    {
        timeout_cnt++;
        if(timeout_cnt>timeout)
            return;
    }

    // 12. Configure the SCL and SDA I/Os as Alternate function Open-Drain.
    GPIO_InitStruct.Mode = GPIO_MODE_AF_OD;
    GPIO_InitStruct.Pull = GPIO_PULLUP;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
    GPIO_InitStruct.Alternate = GPIO_AF4_I2C3;

    GPIO_InitStruct.Pin = I2C3_SCL_PIN;
    HAL_GPIO_Init(I2C3_SCL_PORT, &GPIO_InitStruct);

    GPIO_InitStruct.Pin = I2C3_SDA_PIN;
    HAL_GPIO_Init(I2C3_SDA_PORT, &GPIO_InitStruct);

    HAL_GPIO_WritePin(I2C3_SCL_PORT, I2C3_SCL_PIN, GPIO_PIN_SET);
    HAL_GPIO_WritePin(I2C3_SDA_PORT, I2C3_SDA_PIN, GPIO_PIN_SET);

    // 13. Set SWRST bit in I2Cx_CR1 register.
    instance->Instance->CR1 |= 0x8000;

    asm("nop");

    // 14. Clear SWRST bit in I2Cx_CR1 register.
    instance->Instance->CR1 &= ~0x8000;

    asm("nop");

    // 15. Enable the I2C peripheral by setting the PE bit in I2Cx_CR1 register
    instance->Instance->CR1 |= 0x0001;

    // Call initialization function.
    HAL_I2C_Init(instance);
}

The Problem is, this routine comes never further than step 3, while (GPIO_PIN_SET != HAL_GPIO_ReadPin(I2C3_SDA_PORT, I2C3_SDA_PIN)) and will then return. So , the SDA cannot be set to high anymore. Has anyone an Idea how I could unlock the bus? The Busy flag is never set low after an error occured.

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  • \$\begingroup\$ Are you sure that it's not a slave holding the bus? \$\endgroup\$ – vini_i Jan 25 '18 at 9:37
  • \$\begingroup\$ The SDA line get hold low the whole time and the SCL line high. So this looks like a standard I2C bus lock to me No, that is not a standard lock up. A slave stopping the master holds the SCL line low, not the SDA (see I2C standard). Are the wires swapped? \$\endgroup\$ – Oldfart Jan 25 '18 at 9:51
  • 1
    \$\begingroup\$ @oldfart There is no such thing as a standard lock if everything was working per I2C standard. Therefore when a lock happens it means something went outside of the standard. I2C has one of the highest instances of misapplied standard or outright buggy implementation for both masters and slaves. Also, as the OP answered their own question, a slave was holding the bus. \$\endgroup\$ – vini_i Jan 25 '18 at 10:59
1
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Ok, I solved it, it was the slave and by moving the clock line up and down it unlocked the bus:

void I2C3_ClearBusyFlagErratum(I2C_HandleTypeDef *instance)
{
    GPIO_InitTypeDef GPIO_InitStruct;
    int timeout =100;
    int timeout_cnt=0;

    // 1. Clear PE bit.
    instance->Instance->CR1 &= ~(0x0001);

    //  2. Configure the SCL and SDA I/Os as General Purpose Output Open-Drain, High level (Write 1 to GPIOx_ODR).
    GPIO_InitStruct.Mode         = GPIO_MODE_OUTPUT_OD;
    GPIO_InitStruct.Alternate    = GPIO_AF4_I2C3;
    GPIO_InitStruct.Pull         = GPIO_PULLUP;
    GPIO_InitStruct.Speed        = GPIO_SPEED_FREQ_HIGH;

    GPIO_InitStruct.Pin          = I2C3_SCL_PIN;
    HAL_GPIO_Init(I2C3_SCL_PORT, &GPIO_InitStruct);
    HAL_GPIO_WritePin(I2C3_SCL_PORT, I2C3_SCL_PIN, GPIO_PIN_SET);

    GPIO_InitStruct.Pin          = I2C3_SDA_PIN;
    HAL_GPIO_Init(I2C3_SDA_PORT, &GPIO_InitStruct);
    HAL_GPIO_WritePin(I2C3_SDA_PORT, I2C3_SDA_PIN, GPIO_PIN_SET);


    // 3. Check SCL and SDA High level in GPIOx_IDR.
    while (GPIO_PIN_SET != HAL_GPIO_ReadPin(I2C3_SCL_PORT, I2C3_SCL_PIN))
    {
        timeout_cnt++;
        if(timeout_cnt>timeout)
            return;
    }

    while (GPIO_PIN_SET != HAL_GPIO_ReadPin(I2C3_SDA_PORT, I2C3_SDA_PIN))
    {
        //Move clock to release I2C
        HAL_GPIO_WritePin(I2C3_SCL_PORT, I2C3_SCL_PIN, GPIO_PIN_RESET);
        asm("nop");
        HAL_GPIO_WritePin(I2C3_SCL_PORT, I2C3_SCL_PIN, GPIO_PIN_SET);

        timeout_cnt++;
        if(timeout_cnt>timeout)
            return;
    }

    // 4. Configure the SDA I/O as General Purpose Output Open-Drain, Low level (Write 0 to GPIOx_ODR).
    HAL_GPIO_WritePin(I2C3_SDA_PORT, I2C3_SDA_PIN, GPIO_PIN_RESET);

    //  5. Check SDA Low level in GPIOx_IDR.
    while (GPIO_PIN_RESET != HAL_GPIO_ReadPin(I2C3_SDA_PORT, I2C3_SDA_PIN))
    {
        timeout_cnt++;
        if(timeout_cnt>timeout)
            return;
    }

    // 6. Configure the SCL I/O as General Purpose Output Open-Drain, Low level (Write 0 to GPIOx_ODR).
    HAL_GPIO_WritePin(I2C3_SCL_PORT, I2C3_SCL_PIN, GPIO_PIN_RESET);

    //  7. Check SCL Low level in GPIOx_IDR.
    while (GPIO_PIN_RESET != HAL_GPIO_ReadPin(I2C3_SCL_PORT, I2C3_SCL_PIN))
    {
        timeout_cnt++;
        if(timeout_cnt>timeout)
            return;
    }

    // 8. Configure the SCL I/O as General Purpose Output Open-Drain, High level (Write 1 to GPIOx_ODR).
    HAL_GPIO_WritePin(I2C3_SCL_PORT, I2C3_SCL_PIN, GPIO_PIN_SET);

    // 9. Check SCL High level in GPIOx_IDR.
    while (GPIO_PIN_SET != HAL_GPIO_ReadPin(I2C3_SCL_PORT, I2C3_SCL_PIN))
    {
        timeout_cnt++;
        if(timeout_cnt>timeout)
            return;
    }

    // 10. Configure the SDA I/O as General Purpose Output Open-Drain , High level (Write 1 to GPIOx_ODR).
    HAL_GPIO_WritePin(I2C3_SDA_PORT, I2C3_SDA_PIN, GPIO_PIN_SET);

    // 11. Check SDA High level in GPIOx_IDR.
    while (GPIO_PIN_SET != HAL_GPIO_ReadPin(I2C3_SDA_PORT, I2C3_SDA_PIN))
    {
        timeout_cnt++;
        if(timeout_cnt>timeout)
            return;
    }

    // 12. Configure the SCL and SDA I/Os as Alternate function Open-Drain.
    GPIO_InitStruct.Mode = GPIO_MODE_AF_OD;
    GPIO_InitStruct.Pull = GPIO_PULLUP;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
    GPIO_InitStruct.Alternate = GPIO_AF4_I2C3;

    GPIO_InitStruct.Pin = I2C3_SCL_PIN;
    HAL_GPIO_Init(I2C3_SCL_PORT, &GPIO_InitStruct);

    GPIO_InitStruct.Pin = I2C3_SDA_PIN;
    HAL_GPIO_Init(I2C3_SDA_PORT, &GPIO_InitStruct);

    HAL_GPIO_WritePin(I2C3_SCL_PORT, I2C3_SCL_PIN, GPIO_PIN_SET);
    HAL_GPIO_WritePin(I2C3_SDA_PORT, I2C3_SDA_PIN, GPIO_PIN_SET);

    // 13. Set SWRST bit in I2Cx_CR1 register.
    instance->Instance->CR1 |= 0x8000;

    asm("nop");

    // 14. Clear SWRST bit in I2Cx_CR1 register.
    instance->Instance->CR1 &= ~0x8000;

    asm("nop");

    // 15. Enable the I2C peripheral by setting the PE bit in I2Cx_CR1 register
    instance->Instance->CR1 |= 0x0001;

    // Call initialization function.
    HAL_I2C_Init(instance);
}
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