Reading data from LSM6DS3 Sensor via I2C using nRF52 DK

[Hussein]

Hi 

I'm a total beginner here and I have the gyroscope sensor LSM6DS3 and I have the nRF52 DK

I want to read the sensor's data via I2C (i.e. using SDA and SCL pins) using the nRF52 DK

I have downloaded the SEGGER Embedded studio and I have tried to run some of the ready examples to understand how the code works, but unfortunately, I didn't understand the code of any example expect this project "blinky_pca_10040" 

I can build and run any of the examples to the DK successfully without problems, but my problem is that I don't understand the codes!

I feel like understanding the code of any project is so difficult and I need to connect my sensor to the DK and I don't even know what to do or where to start!

I would really appreciate your help in this issue and I totally appreciate your patience with my ignorance of this matter.

[BinderT]

Hi,

Have a look here what component do.

crash coarse.

const nrf_drv_twi_config_t twi_lm75b_config
setup for the twi

err_code = nrf_drv_twi_init(&m_twi, &twi_lm75b_config, twi_handler, NULL);
start twi
params: twi instance, config, event handler, context (void pointer).

err_code = nrf_drv_twi_rx(&m_twi, LM75B_ADDR, &m_sample, sizeof(m_sample));
read data,
params: twi instance, address, rx buffer, size of rx buffer in bytes.

err_code = nrf_drv_twi_tx(&m_twi, LM75B_ADDR, reg, sizeof(reg), false);
send data:
params: twi instance, address, tx buffer, size of tx buffer in bytes, send no stop.


void twi_handler(nrf_drv_twi_evt_t const * p_event, void * p_context)
events:
NRF_DRV_TWI_EVT_DONE: RX/TX done.
p_event->xfer_desc.type == NRF_DRV_TWI_XFER_RXNRF_DRV_TWI_XFER_RX: receive is done

[Hussein]

To be honest, I didn't understand anything from the reply. 

I spent a lot of time trying to understand what you mean, but unfortunately I couldn't.

As I mentioned in the main post, I'm a total beginner. So, I need something like a simple guide or simple steps to follow. 

I can even read any document even if it is a long one but only if it can help and can give me the fundamentals of using the I2C on the nRF52 DK

I really appreciate if you can make things clearer for me.

Thank you

[BinderT]

Hussein said:

I'm a total beginner

Apologies this is very difficult to gauge this. Hopefully this is more understandable.

TWI = I2C.

In the examples SDK\examples\peripheral\twi_sensor

1.

/* TWI instance ID. */
#define TWI_INSTANCE_ID     0

/* TWI instance. */
static const nrf_drv_twi_t m_twi = NRF_DRV_TWI_INSTANCE(TWI_INSTANCE_ID);

These refer to the hardware TWI instant you are using. The nRF52s has more than one hardware TWI interface.

2.

/**
 * @brief Function for setting active mode on MMA7660 accelerometer.
 */
void LM75B_set_mode(void)
{
    ret_code_t err_code;

    /* Writing to LM75B_REG_CONF "0" set temperature sensor in NORMAL mode. */
    uint8_t reg[2] = {LM75B_REG_CONF, NORMAL_MODE};
    err_code = nrf_drv_twi_tx(&m_twi, LM75B_ADDR, reg, sizeof(reg), false);
    APP_ERROR_CHECK(err_code);
    while (m_xfer_done == false);

    /* Writing to pointer byte. */
    reg[0] = LM75B_REG_TEMP;
    m_xfer_done = false;
    err_code = nrf_drv_twi_tx(&m_twi, LM75B_ADDR, reg, 1, false);
    APP_ERROR_CHECK(err_code);
    while (m_xfer_done == false);
}

uint8_t reg[2] is the data buffer to be sent via TWI. In this case the register and data.

3.

err_code = nrf_drv_twi_tx(&m_twi, LM75B_ADDR, reg, sizeof(reg), false);
APP_ERROR_CHECK(err_code);
while (m_xfer_done == false);

3.1
err_code = nrf_drv_twi_tx(&m_twi, LM75B_ADDR, reg, sizeof(reg), false);
send data:
params: twi instance, address, tx buffer, size of tx buffer in bytes, send no stop.

3.2
This sends data via the TWI.
m_twi: the hardware TWI instant being used ref 1.
LM75B_ADDR: the address of the TWI device.
reg: is the data to be sent ref 2.
sizeof(reg): the length of data to be sent in bytes. sizeof(reg) = 2
false: send a stop (send_no_stop). true don't send a TWI stop.

Returns a error code and check it.
Then wait for the TWI to finish ref 6.

4.

void twi_init (void)
{
    ret_code_t err_code;

    const nrf_drv_twi_config_t twi_lm75b_config = {
       .scl                = ARDUINO_SCL_PIN,
       .sda                = ARDUINO_SDA_PIN,
       .frequency          = NRF_DRV_TWI_FREQ_100K,
       .interrupt_priority = APP_IRQ_PRIORITY_HIGH,
       .clear_bus_init     = false
    };

    err_code = nrf_drv_twi_init(&m_twi, &twi_lm75b_config, twi_handler, NULL);
    APP_ERROR_CHECK(err_code);

    nrf_drv_twi_enable(&m_twi);
}

4.1
const nrf_drv_twi_config_t twi_lm75b_config
setup for the twi

.scl pin used for SCL on the nrf.
.sda pin used for SDA on the nrf.
.frequency speed of the TWI interface
.interrupt_priority how important is the interrupt of TWI.
.clear_bus_init can't remember.

4.2
err_code = nrf_drv_twi_init(&m_twi, &twi_lm75b_config, twi_handler, NULL);
start twi
params: twi instance, config, event handler, context (void pointer).

m_twi: the hardware TWI instant being used ref 1.
twi_lm75b_config: config for the TWI ref 4.1.
twi_handler: function to handle events from the TWI ref 6.
NULL: not in the scope to explain this just leave it as NULL.

Returns a error code and check it.

4.3
nrf_drv_twi_enable(&m_twi);
enable/start the TWI interface
m_twi: the hardware TWI instant being used ref 1.

5.

static void read_sensor_data()
{
    m_xfer_done = false;

    /* Read 1 byte from the specified address - skip 3 bits dedicated for fractional part of temperature. */
    ret_code_t err_code = nrf_drv_twi_rx(&m_twi, LM75B_ADDR, &m_sample, sizeof(m_sample));
    APP_ERROR_CHECK(err_code);
}

err_code = nrf_drv_twi_rx(&m_twi, LM75B_ADDR, &m_sample, sizeof(m_sample));
read data,
params: twi instance, address, rx buffer, size of rx buffer in bytes.

m_twi the hardware TWI instant being used ref 1.
LM75B_ADDR the address of the TWI device.
m_sample holdes the data that is read from the TWI device.
sizeof(m_sample) the number of bytes to read.

NOTE: this is typically used after a nrf_drv_twi_tx(); with no stop set to true. Please refer to the TWI spec on how to read a device.

6.

/**
 * @brief TWI events handler.
 */
 //function to handle events
void twi_handler(nrf_drv_twi_evt_t const * p_event, void * p_context)
{
    switch (p_event->type) // what event happend
    {
        case NRF_DRV_TWI_EVT_DONE: // TWI is done doing stuff
            if (p_event->xfer_desc.type == NRF_DRV_TWI_XFER_RX) //was the last tranfer a read 
            {
                data_handler(m_sample);// handle the read data
            }
            m_xfer_done = true; //tells the app the the TWI is done doing stuff
            break;
        default:
            break;
    }
}

Please read the comments in the code.