nRF52832 with MPU9250 using i2c (TWI) on SDK15.2, SD132, Segger Embedded Studio

[usmanmehmood55]

Hi. 

I'm trying to integrate the MPU9250 with nRF52832 using i2c (TWI) on my nRF52-DK

I have found various libraries but none of them are working on my hardware. All of them have compilation errors and missing files (or parts inside files)

If anyone has made a project integrating these two and using Segger Embedded Studio for compilation and flashing, please give me some advice as to how I can do it on my side too? 

Any help would be appreciated.

Best regards,

Usman

[haakonsh]

I suggest you ask Invensense for their driver and libraries, you should only need to implement the R/W functions with our TWI driver API. 

-Edit:

From the invensense website: "Note: The MPU-9250 is marked as EOL and is not recommended for new designs".

https://invensense.tdk.com/products/motion-tracking/9-axis/mpu-9250/ 

There's also little stock left at distributors. 

[usmanmehmood55]

Hi. 

I will try to do that as well. 

I was hesitant to make my own R/W functions, but I might have to do it in the end. 

Can you please give me a guide/advice on how to do so?

Regards. 

[awneil]

usmanmehmood55 said:

I was hesitant to make my own R/W functions,

That's just implementing the basic I2C bus access - for these, what Slave you use is irrelevant.

so see the I2C drivers & examples in the SDK

https://infocenter.nordicsemi.com/topic/sdk_nrf5_v17.0.2/twi_scanner_example.html

https://infocenter.nordicsemi.com/topic/sdk_nrf5_v17.0.2/twi_sensor_example.html

https://infocenter.nordicsemi.com/topic/sdk_nrf5_v17.0.2/twi_transaction_mgr_example.html

https://infocenter.nordicsemi.com/topic/sdk_nrf5_v17.0.2/twi_master_with_twis_slave_example.html

[usmanmehmood55]

Hi. I'm looking at Nordic's twi_master.h library. And there is something very confusing. 

There are two .c fies. One is twi_hw_master.c and other is twi_sw_master.c 

Now, each of these files contain their own definitions of the functions twi_master_transfer, and twi_master_init. And the functions are not being overloaded either. They have the same return type, same inputs. 
For example, here's twi_master_transfer:
In twi_hw_master.c

bool twi_master_transfer(uint8_t address,
                         uint8_t *data,
                         uint8_t data_length,
                         bool issue_stop_condition)
{
    bool transfer_succeeded = true;

    transfer_succeeded &= twi_master_issue_startcondition();
    transfer_succeeded &= twi_master_clock_byte(address);

    if (address & TWI_READ_BIT)
    {
        /* Transfer direction is from Slave to Master */
        while (data_length-- && transfer_succeeded)
        {
            // To indicate to slave that we've finished transferring last data byte
            // we need to NACK the last transfer.
            if (data_length == 0)
            {
                transfer_succeeded &= twi_master_clock_byte_in(data, (bool)false);
            }
            else
            {
                transfer_succeeded &= twi_master_clock_byte_in(data, (bool)true);
            }
            data++;
        }
    }
    else
    {
        /* Transfer direction is from Master to Slave */
        while (data_length-- && transfer_succeeded)
        {
            transfer_succeeded &= twi_master_clock_byte(*data);
            data++;
        }
    }

    if (issue_stop_condition || !transfer_succeeded)
    {
        transfer_succeeded &= twi_master_issue_stopcondition();
    }

    return transfer_succeeded;
}

And in twi_sw_master.c

bool twi_master_transfer(uint8_t   address,
                         uint8_t * data,
                         uint8_t   data_length,
                         bool      issue_stop_condition)
{
    bool transfer_succeeded = false;
    if (data_length > 0 && twi_master_clear_bus())
    {
        NRF_TWI1->ADDRESS = (address >> 1);

        if ((address & TWI_READ_BIT))
        {
            transfer_succeeded = twi_master_read(data, data_length, issue_stop_condition);
        }
        else
        {
            transfer_succeeded = twi_master_write(data, data_length, issue_stop_condition);
        }
    }
    return transfer_succeeded;
}

This seems very strange to me. Which one is the code supposed to use? 

[haakonsh]

It's a SW vs HW implementation, use the HW one.

[awneil]

haakonsh said:

It's a SW vs HW implementation

hence the _sw_ and _hw_ in the file names!

[usmanmehmood55]

I managed to make it work. Thank you so much for your help. 

[haakonsh]

Glad to hear, good job! :D