STEVAL-STMDLTE (BG96) MODEM LTE with NRF52840 using libuarte

Question

We are trying to integrate the STEVAL_MODEM_BG96 chip into the NRF52840 for rapid prototyping. Trying to interface nrf52840 with the STEVAL-

STMODLTE chip via UART. Connecting the RX, TX and gnd and seeing the "AT" command after the UART initializes, the modem does not respond. The

question is, did I miss something in the soft ? or do you have any idea please help me, i am stuck. I'm sure I'm missing something simpler, we tried the

same way using MCU (nrf52) with FDTI serial port and it worked fine. Could you help me please? Thanks in advance.

Pins using for UARTE0 : NRF_GPIO_PIN_MAP(1,2), //TX_PIN_NUMBER, NRF_GPIO_PIN_MAP(1,3), //RX_PIN_NUMBER,

by information the chip uses a level shifter to convert the 1.8v to 3.3v, so I am connected in 3.3v between the nRF52 and the modem

Please can you help me ! , I'm really stuck . 

Best Regards,

Lora



Sniffer using FTDI

and sometimes the software crashes here NRF_BREAKPOINT_COND



STEVAL-STMODLTE circuit schematic

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/** @file
 * @defgroup libuarte_example_main main.c
 * @{
 * @ingroup libuarte_example
 * @brief Libuarte Example Application main file.
 *
 * This file contains the source code for a sample application using libuarte.
 *
 */

#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include "nrf_libuarte_async.h"
#include "nrf_drv_clock.h"
#include <bsp.h>
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"
#include "nrf_queue.h"
#include "nrf_delay.h"


#define MODEM_PWR_EN_GPIO_PORT                                      (NRF_GPIO_PIN_MAP(1,4)) 
#define GPIO_PIN_RESET                                              (0)
#define GPIO_PIN_SET                                                (1)       
#define SIZE_BUFFER_RX                                              (50)
#define BG96_BOOT_TIME                                              (5500U)  


uint8_t CMD_ATI[] = "ATI\n";
uint16_t size_cmd = sizeof(CMD_ATI);


unsigned char buffer_rx[SIZE_BUFFER_RX];
uint32_t numbre_data_received = 0;


NRF_LIBUARTE_ASYNC_DEFINE(libuarte, 0, 0, 0, NRF_LIBUARTE_PERIPHERAL_NOT_USED, 255, 3);

static volatile bool m_resp_bg96_ok = false;
bool m_loopback_phase = false;

typedef struct {
    uint8_t * p_data;
    uint32_t length;
} buffer_t;

NRF_QUEUE_DEF(buffer_t, m_buf_queue, 10, NRF_QUEUE_MODE_NO_OVERFLOW);

static uint8_t command[]="123456789012345123456534623465351235412344123412341234";


/**
 * @brief Function used to wakeup the MODEM 
 */
void sys_ctrl_bg96_power_on(void)
{

  /* Reference: Quectel BG96 Hardware Design V1.4
  *  PWRKEY   connected to MODEM_PWR_EN (inverse pulse)
  *  RESET_N  connected to MODEM_RST    (inverse)
  *
  * Turn ON module sequence
  *
  *                PWRKEY  PWR_EN  modem_state
  * init             0       1      OFF
  * T=0 ms           1       0      OFF
  * T1=30 ms         0       1      BOOTING
  * T2=T1+500 ms     1       0      BOOTING
  * T3=T1+4800 ms    1       0      RUNNING
  */

  /* First, turn OFF module in case it was not switched off correctly (can occur after
   *  a manual reset).
   * Set PWR_EN to 0 at least 650ms
   */
  
  nrf_gpio_cfg_output(MODEM_PWR_EN_GPIO_PORT);
  
  nrf_gpio_pin_write(MODEM_PWR_EN_GPIO_PORT, GPIO_PIN_SET);
  nrf_delay_ms(700U);
  nrf_gpio_pin_write(MODEM_PWR_EN_GPIO_PORT, GPIO_PIN_RESET);
  nrf_delay_ms(1000U);

  /* Power ON sequence */
  /* Set PWR_EN to 1 (initial state) */
  nrf_gpio_pin_write(MODEM_PWR_EN_GPIO_PORT, GPIO_PIN_SET);
  nrf_delay_ms(50U);

  /* Set PWR_EN to 0 during at least 30ms as defined by Quectel */
  nrf_gpio_pin_write(MODEM_PWR_EN_GPIO_PORT, GPIO_PIN_RESET);
  nrf_delay_ms(30U);

  /* Set PWR_EN to 1 during at least 500ms */
  nrf_gpio_pin_write(MODEM_PWR_EN_GPIO_PORT, GPIO_PIN_SET);
  nrf_delay_ms(510U);

  /* Set PWR_EN to 0 */
  nrf_gpio_pin_write(MODEM_PWR_EN_GPIO_PORT, GPIO_PIN_RESET);

  /* wait for Modem to complete its booting procedure */
  /*"Waiting %d millisec for modem running...", BG96_BOOT_TIME)*/
  nrf_delay_ms(BG96_BOOT_TIME);
  /* ... done */
}


void send_command(uint8_t cmd[], uint16_t size)
{
    ret_code_t err_code;

    memset(command, 0, sizeof(command));

    for (int i=0; i<size; i++)
    {
        command[i] = cmd[i];   
    }

    do {
        err_code = nrf_libuarte_async_tx(&libuarte, command, sizeof(command));
        }
    while (err_code == NRF_ERROR_BUSY);

    APP_ERROR_CHECK(err_code);

    nrf_delay_ms(300);
}


void uart_event_handler(void * context, nrf_libuarte_async_evt_t * p_evt)
{
    nrf_libuarte_async_t * p_libuarte = (nrf_libuarte_async_t *)context;
    ret_code_t ret;

    switch (p_evt->type)
    {
        case NRF_LIBUARTE_ASYNC_EVT_ERROR:
            break;
        case NRF_LIBUARTE_ASYNC_EVT_RX_DATA:
            
            if((unsigned char)*(p_evt->data.rxtx.p_data) !=0 )
            {
                buffer_rx[numbre_data_received]=(unsigned char)*(p_evt->data.rxtx.p_data);
                numbre_data_received = numbre_data_received + 1;
            }

            if((buffer_rx[numbre_data_received - 1] == '\r') || 
                (buffer_rx[numbre_data_received - 1 ] == '\n'))
            {
                char * find_BG96 = strstr((const char *)buffer_rx, (const char *)"BG96");

                if( find_BG96 == NULL)
                {
                    send_command("ATI\n", sizeof("ATI\n"));
                    send_command("AT\n",sizeof("AT\n"));
                    send_command("AT+GSN\n",sizeof("AT+GSN\n"));
                    send_command("AT+CSQ\n",sizeof("AT+CSQ\n"));
                    send_command("AT+CMGF=1\n",sizeof("AT+CMGF=1\n"));
                }
                else
                {
                    for (int i = 0; i < LEDS_NUMBER; i++)
                    {
                    bsp_board_led_invert(i);
                    nrf_delay_ms(500);
                    }
                }

                if( numbre_data_received >= SIZE_BUFFER_RX )
                {
                    memset(buffer_rx, 0, numbre_data_received);
                    numbre_data_received = 0;
                }
             }

              m_loopback_phase = true;
            break;
        case NRF_LIBUARTE_ASYNC_EVT_TX_DONE:
            if (m_loopback_phase)
            {
                nrf_libuarte_async_rx_free(p_libuarte, p_evt->data.rxtx.p_data, p_evt->data.rxtx.length);
            }
            break;
        default:
            break;
    }
}



/**
 * @brief Function for main application entry.
 */
int main(void)
{
    bsp_board_init(BSP_INIT_LEDS);

    //sys_ctrl_bg96_power_on();
    
    ret_code_t ret = nrf_drv_clock_init();
    APP_ERROR_CHECK(ret);
  
    nrf_drv_clock_lfclk_request(NULL);

    ret_code_t err_code = NRF_LOG_INIT(app_timer_cnt_get);
    APP_ERROR_CHECK(err_code);

    NRF_LOG_DEFAULT_BACKENDS_INIT();

    nrf_libuarte_async_config_t nrf_libuarte_async_config = {
            .tx_pin     = NRF_GPIO_PIN_MAP(1,2), //TX_PIN_NUMBER,
            .rx_pin     = NRF_GPIO_PIN_MAP(1,3), //RX_PIN_NUMBER,
            .baudrate   = NRF_UARTE_BAUDRATE_115200,
            .parity     = NRF_UARTE_PARITY_EXCLUDED,
            .hwfc       = NRF_UARTE_HWFC_DISABLED,
            .timeout_us = 100,
            .int_prio   = APP_IRQ_PRIORITY_HIGH,
            .pullup_rx = NRF_GPIO_PIN_PULLUP
    };

    err_code = nrf_libuarte_async_init(&libuarte, &nrf_libuarte_async_config, uart_event_handler, (void *)&libuarte);

    APP_ERROR_CHECK(err_code);

    nrf_libuarte_async_enable(&libuarte);

    send_command("ATI\n", sizeof("ATI\n"));
    send_command("AT\n",sizeof("AT\n"));
    send_command("AT+GSN\n",sizeof("AT+GSN\n"));
    send_command("AT+CSQ\n",sizeof("AT+CSQ\n"));
    send_command("AT+CMGF=1\n",sizeof("AT+CMGF=1\n"));

    while(true)
    {
        NRF_LOG_FLUSH();
    }
}