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

[Lora]

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();
    }
}

[Einar Thorsrud]

Hi,

and sometimes the software crashes here NRF_BREAKPOINT_CON

This is from the error handler, and if you test with a debug build you can check the file name, line number and error code. That should give you a lot to go on (see An introduction to error handling in nRF5 projects).

Sniffer using FTDI

It is not easy to say much without knowing more, but it looks like there could be a baud rate issue. Is the baud rate configuration the same on both ends? And do both sides use an accurate clock source? As you are already using the clock driver that could be accomplished on the nRF side by calling nrf_drv_clock_hfclk_request().

[Lora]

Hi Einar,

Thank you for your feedback .

I work on a project, the objective is to communicate nRF52840 with (  STEVAL-STMODLTE puce with modem BG96  steval-stmodlte ) .

I use an example libuarte in SDK nRF52840, the problem is that I don't receive the correct data from the modem .

I attached a screenshot of the data received . and yesterday i did a test, i communicated with a direct FTDI cable on the tx, rx, gnd of the modem and PC using a tool to send AT command and i received the same incorrect data .

By info on the chip STEVAL-STMODLTE there is a usb port to send AT commands and it works well when you connect to the micro usb port, and also at the output of the chip i measure 3,3v and at the output of the modem BG96 i measure 1,8v because there is a shifter level in schematics  Link ( 8 . Schematic diagrams).

Concerning the baudrate, when I connect in usb micro, I send the command AT : AT+IPR? it responds well 115200  and in MCU nRF52 i config the baudrate as 115200 .

Thank you for your help .

Best regards,

[Einar Thorsrud]

Hi,

Lora said:

I don't receive the correct data from the modem .

In what way is it not correct? Wrong amount of data/length, or corrupted data? please elaborate. Also, what does the data look like if you log it from the nRF? Is it the same as when  you dump it from the FTDI connected to a computer, or different?

Lora said:

and yesterday i did a test, i communicated with a direct FTDI cable on the tx, rx, gnd of the modem and PC using a tool to send AT command and i received the same incorrect data .

It seems like you are having issues communicating with the modem also when you do not use the nRF? For that I ask you to contact ST, as that is their product and I am not able to support that.

Lora said:

and also at the output of the chip i measure 3,3v and at the output of the modem BG96 i measure 1,8v because there is a shifter level in schematics  Link ( 8 . Schematic diagrams).

I will just assume that this works properly, for details you need to discuss with ST.

Lora said:

Concerning the baudrate, when I connect in usb micro, I send the command AT : AT+IPR? it responds well 115200  and in MCU nRF52 i config the baudrate as 115200 .

The baud rate could be wrong (meaning not the same) even if you have configured the same baud rate on all devices. If the clocks are inaccurate and too different, you will still have problems (UART is asynchronous after all).

[Lora]

Hi Einar,

here is the kind of data when I connect directly to the tx, rx, and gnd of the modem with an FTDI using a tool to send the data

[Lora]

and I have the same thing when I view the receive buffer with the nRF52 MCU

[Einar Thorsrud]

This is between your PC and the BG96, right? If so, you need to ask ST about it.

[Lora]

I it's between the PC and the modem by the uart of the modem ( NOK)