Read Function with TWI/TWIM legacy and NRFX

[polimarte]

Hi I am using nRF52 DK, nRF52832 and a sensor. The TWI communication is described as :

and : 

I tried to use the Legacy of TWI drivers in order to implement a read function able to read the registers. As well i tried to use nrfx module with separate NRFX_TWIM_XFER_DESC_TX/RX. Both have some problems. Before to try to resolve my issues i am wondering if i am on the right path using these functions.

I would like to use the legacy beacuse i am working to an older version of SDK (14.2.0) and i don't want to integrate it with the nrfx module if possible.

Are these liberies able to implement a correct communication in my case or there are other functions more suitable to define my read function?

Thanks,

polimarte

[Vidar Berg]

Hello,

The same transfer macros should be available in the legacy driver, please take a look at the driver documentation here: TWI master.

Also, below I have included an example I made to interface with the Sensirion sht3x. It demonstrate how the transfer macros can be used to set up a complete transaction. Hopefully it may be useful as a reference.

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/** @file
 * @defgroup tw_sensor_example main.c
 * @{
 * @ingroup nrf_twi_example
 * @brief TWI Sensor Example main file.
 *
 * This file contains the source code for a sample application using TWI.
 *
 */

#include <stdio.h>
#include "boards.h"
#include "app_util_platform.h"
#include "app_error.h"
#include "nrf_drv_twi.h"
#include "nrf_delay.h"


#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

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

/* Common addresses definition for temperature sensor. */
#define SHT3x_ADDRESS                   (0x45U)
#define SHT3x_MEAS_CMD_H                {0x2c, 0x06}                       /**<Start high repeatability measurement with clock stretching*/

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


/**
 * @brief Function for handling data from temperature sensor.
 *
 * @param[in] temp          Temperature in Celsius degrees read from sensor.
 */
__STATIC_INLINE void data_handler(nrf_drv_twi_evt_t const * p_event)
{
    uint16_t      raw_value;
    float         temperature;
    uint16_t      humidity;
    
    /* Raw data conversion. We are ignoring the checksum value here */ 
    raw_value = uint16_big_decode(&p_event->xfer_desc.p_secondary_buf[0]); /* Swap byte order to little endian */
    
    temperature = 175 * (uint16_t)raw_value / 65535.0f -45.0f;

    raw_value = uint16_big_decode(&p_event->xfer_desc.p_secondary_buf[3]);
    humidity = 100.0f * raw_value / 65535.0f;
    
    NRF_LOG_INFO("Temperature: "NRF_LOG_FLOAT_MARKER" Celsius degrees.", NRF_LOG_FLOAT(temperature));
    NRF_LOG_INFO("Humidity: %d%%", humidity);
}

/**
 * @brief TWI events handler.
 */
void twi_handler(nrf_drv_twi_evt_t const * p_event, void * p_context)
{
    switch (p_event->type)
    {
        case NRF_DRV_TWI_EVT_DONE:
            if (p_event->xfer_desc.type == NRF_DRV_TWI_XFER_TXRX)
            {
                data_handler(p_event);
            }
            break;
        case NRF_DRV_TWI_EVT_ADDRESS_NACK:
            NRF_LOG_WARNING("Received NRF_DRV_TWI_EVT_ADDRESS_NACK event");
            break;
        case NRF_DRV_TWI_EVT_DATA_NACK:
            NRF_LOG_WARNING("Received NRF_DRV_TWI_EVT_DATA_NACK event");
            break;
        default:
            break;
    }
}

/**
 * @brief UART initialization.
 */
void twi_init (void)
{
    ret_code_t err_code;

    const nrf_drv_twi_config_t twi_sht3x_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_sht3x_config, twi_handler, NULL);
    APP_ERROR_CHECK(err_code);

    nrf_drv_twi_enable(&m_twi);
}

/**
 * @brief Function for reading data from temperature sensor.
 */
static void read_sensor_data()
{  
    uint32_t err_code;
    static uint8_t twim_rx_buf[6];
    static uint8_t twim_tx_buf[] = SHT3x_MEAS_CMD_H;

    nrf_drv_twi_xfer_desc_t xfer_desc = NRF_DRV_TWI_XFER_DESC_TXRX(
        SHT3x_ADDRESS, twim_tx_buf, sizeof(twim_tx_buf), twim_rx_buf, sizeof(twim_rx_buf));

    err_code = nrf_drv_twi_xfer(&m_twi, &xfer_desc, NRF_DRV_TWI_FLAG_TX_NO_STOP);
    if (err_code == NRF_ERROR_BUSY)
    {
        NRF_LOG_INFO("TWIM driver is busy");
    }
    else
    {
        APP_ERROR_CHECK(err_code);
    }
}

/**
 * @brief Function for main application entry.
 */
int main(void)
{
    APP_ERROR_CHECK(NRF_LOG_INIT(NULL));
    NRF_LOG_DEFAULT_BACKENDS_INIT();

    NRF_LOG_INFO("\r\nTWI SHT3x example started.");
    NRF_LOG_FLUSH();
    twi_init();

    while (true)
    {
        nrf_delay_ms(500);
        read_sensor_data();
        NRF_LOG_FLUSH();
    }
}

/** @} */

Best regards,

Vidar