Not able to use nordic proprietary AT-Commands on nrf9160

[jannis]

Hello dear People,

I would be very happy if anyone has an idea how to solve this.

The Problem is the following: I am using nordics lte link controller to connect to nb-iot(<modem/lte_lc.h>), but when opening a socket, it times out... (error 116).
Basically for this testing scenario i adapted the udp sample to make tcp connection and send/receive some data:

The code for opening the socket:

 ip to local port and establish tcp-connection:

int tcp_create_conn_socket(const char * host, int port){

  // conn. init: defining socket parameters
  
  struct sockaddr_in *server4 = ((struct sockaddr_in *)&host_addr);

  server4->sin_family = AF_INET;
  server4->sin_port = htons(port);

  inet_pton(AF_INET, host, &server4->sin_addr);

   
  // bind server ip to local port and establish tcp-connection:

  int err, sockfd;
  sockfd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);  // Creation of TCP-Socket
  if (sockfd < 0) {
    printk("Failed to create TCP socket: %d\n", errno);
    err = -errno;
    goto error;
  }

  err = connect(sockfd, (struct sockaddr *)&host_addr, sizeof(struct sockaddr_in));  // establishing connection
  if (err < 0) {
    printk("Connect failed : %d\n", errno);
    goto error;
  }

  return sockfd;


error:
  tcp_disconnect(sockfd);

  return err;

}

my proj.conf file looks the following:

#
# Copyright (c) 2020 Nordic Semiconductor ASA
#
# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
#

# General config
CONFIG_NEWLIB_LIBC=y
CONFIG_NEWLIB_LIBC_FLOAT_PRINTF=y

CONFIG_NCS_SAMPLES_DEFAULTS=y

CONFIG_LOG=y
CONFIG_LOG_DEFAULT_LEVEL=4
CONFIG_DEBUG_OPTIMIZATIONS=y
CONFIG_LOG_PRINTK=y

CONFIG_ASSERT=y
CONFIG_STACK_SENTINEL=y
CONFIG_LOG_PROCESS_THREAD=y

CONFIG_USE_SEGGER_RTT=y
CONFIG_RTT_CONSOLE=y
CONFIG_UART_CONSOLE=n
CONFIG_LOG_BACKEND_RTT=y
CONFIG_LOG_BACKEND_UART=n

# Network
CONFIG_NETWORKING=y
CONFIG_NET_NATIVE=n
CONFIG_NET_SOCKETS=y
CONFIG_NET_SOCKETS_OFFLOAD=y
CONFIG_NET_SOCKETS_POSIX_NAMES=y

# LTE link control
CONFIG_LTE_LINK_CONTROL=y
CONFIG_LTE_AUTO_INIT_AND_CONNECT=n

# Modem library
CONFIG_NRF_MODEM_LIB=y

# Heap and stacks
CONFIG_HEAP_MEM_POOL_SIZE=1024
CONFIG_MAIN_STACK_SIZE=4096
CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=2048

# LTE parameters
## Network Mode / LTE category
CONFIG_LTE_NETWORK_MODE_LTE_M=n
CONFIG_LTE_NETWORK_MODE_NBIOT=y
#CONFIG_LTE_NETWORK_MODE_NBIOT_GPS=y

## PSM
#CONFIG_UDP_PSM_ENABLE=y
#CONFIG_LTE_PSM_REQ_RPTAU="00100001"
#CONFIG_LTE_PSM_REQ_RAT="00000000"

## eDRX
CONFIG_UDP_EDRX_ENABLE=n
CONFIG_LTE_EDRX_REQ_VALUE_NBIOT="1001"

## RAI
#CONFIG_UDP_RAI_ENABLE=n
#CONFIG_LTE_RAI_REQ_VALUE="4"

the debug output:

*** Booting Zephyr OS build v2.7.99-ncs1  ***
[*] NIS TCP-WRAP TEST-APP
lte-mode: irgend n anderer
D: AT notif: +CEREG: 2,"C37C","01921F0C",9,0,0,"11100000","11100000"

D: Dispatching to 0x178fd
LTE cell changed: Cell ID: 26353420, Tracking area: 50044
D: AT notif: +CSCON: 1

D: Dispatching to 0x17479
RRC mode: Connected
D: AT notif: +CEREG: 1,"C37C","01921F0C",9,,,"00000010","00011111"

D: Dispatching to 0x178fd
Network registration status: Connected - home network
PSM parameter update: TAU: 18600, Active time: 4
lte-mode: nbiot-lte
cesq-response: ERROR

selected band: 
ERROR

Connect failed : 116
[!] Err: Not able to initialize and establish TCP server connection
D: AT notif: +CSCON: 0

D: Dispatching to 0x17479
RRC mode: Idle

my main.c:

void main(void)
{
  printk("[*] NIS TCP-WRAP TEST-APP\n");

  k_work_init_delayable(&server_transmission_work, transmit_msg); // init worker thread, since modem conn is not reliable from isr

  if(init_lte() < 0) return;
  //if(init_button() < 0) return;
  //if(init_led() < 0) return;

  if (ask_for_current_band() < 0) return;


  sockfd = tcp_create_conn_socket("194.13.83.174", 4444);

  if (sockfd < 0) {
    printk("[!] Err: Not able to initialize and establish TCP server connection\n");
    return;
  }

  printk("[*] Connected to server\n");
  server_connected = true;
  
  tcp_send_msg(sockfd, "hallo was geht?", 15);
  
  wait_for_incoming();

  tcp_disconnect(sockfd);  
  return;
}

the connection to the server used to work on my thingy, but on the custom devboard my employer wants me to work with there the tcp-connection always times out.
One big difference is on the thingy i was using lte-m and the devboard sim only supports nb-iot which is why I configured the project to use nb-iot only.

this is the code i use to connect to the nb-iot network:

int lte_modem_connect(){
  int err;
  enum lte_lc_lte_mode a;
  k_work_init_delayable(&lte_at_work, get_at);
  if (IS_ENABLED(CONFIG_LTE_AUTO_INIT_AND_CONNECT)) {
          /* Do nothing, modem is already configured and LTE connected. */
  } else {
          
          lte_lc_lte_mode_get(&a);
          switch(a){
            case LTE_LC_SYSTEM_MODE_PREFER_AUTO:
              printk("lte_mode: prefer auto\n");
              break;
            case LTE_LC_SYSTEM_MODE_PREFER_LTEM:
              printk("lte_mode: prefer lte-m\n");
              break;
            case LTE_LC_SYSTEM_MODE_PREFER_NBIOT:
              printk("lte-mode: prefer-nbiot");
              break;
            default:
              printk("lte-mode: irgend n anderer\n");
              break;
          }
          printk("");
          err = lte_lc_connect_async(lte_handler);
          if (err) {
                  printk("Connecting to LTE network failed, error: %d\n",
                         err);
                  return;
          }
          //k_msleep(500);
          //k_work_schedule(&lte_at_work, K_NO_WAIT);
  }
  k_sem_take(&lte_connected, K_FOREVER);
  lte_lc_lte_mode_get(&a);
  switch(a){
    case LTE_LC_SYSTEM_MODE_PREFER_AUTO:
      printk("lte_mode: prefer auto\n");
      break;
    case LTE_LC_LTE_MODE_LTEM:
      printk("lte_mode: prefer lte-m\n");
      break;
    case LTE_LC_LTE_MODE_NBIOT:
      printk("lte-mode: nbiot-lte\n");
      break;
    default:
      printk("lte-mode: irgend n anderer\n");
      break;
  }
}

Now when I call some at commands (using nrf_modem_at_cmd from  <nrf_modem_at.h>) for example to see which band is in use/available on the modem:

int ask_for_current_band(){
  char response[64];
  nrf_modem_at_cmd(response, 64, "AT%CESQ=1");
  printk("cesq-response: %s\n", response);
  if (nrf_modem_at_cmd_async(band_at_callback, "AT%XCBAND=?")) return -1;
}

I always get an error (see debug output above), but only when using nordics proprietary at-commands (AT%<command>, like mentioned in https://infocenter.nordicsemi.com/pdf/nrf91_at_commands_v1.0.pdf). Standard AT-Commands (those with a +) seem to work fine....

Do i have to do extra configuration when I want to use the nordic proprietary at-commands like XCBAND or when I am using NB-IOT in general?

My guess so far is that the connection time out is occuring, because nordics lte link controller is eventually also not able to use those to open a socket.

Any help is appreciated and I would be very grateful.

Have a nice day folks,

Jannis

PS: my setup:

Modem firmware version 1.2.3

nrf-connect sdk version 1.9.0

Zephyr OS build v2.7.99-ncs1

Nordic nrf9160 rev2

[jannis]

Hey :),

All right, I just realized that using those proprietary at-commands is only possible when externally controlling the serial lte-modem.

But that still leaves me with the timed out connection and I am back to the beginning of the search for the cause.

I would be very happy if anyone has an idea.

greetings Jannis

[Charlie]

Hi Jannis,

I have two suggestions:

1) Can you verify your codes with thingy works with the NB-IoT network?

2) Can you test your custom board with nRF9160: Serial LTE modem — nRF Connect SDK 1.9.1 documentation (nordicsemi.com) TCP commands? You need to verify if the HW especially the antenna has issues or not.

Best regards,

Charlie

[jannis]

Hey Charlie, thank you for your reply!,

that's a good idea, i only tested on the thingy with lte-m, which worked, i just tested it on the thingy91 with nb-iot and the connection process times out here as well.

I did some research but whenever I look up Information about nb-iot most of it is for businesses highlighting its advantages for their products, but not so many technically details or processes, we use a deutsche Telekom sim-card specific for nb-iot. Is it common that there is some registration necessary to connect to the internet/pdn?(softwarewise during the connection-process, like with this method: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/1.3.1/nrf/include/modem/lte_lc.html#_CPPv419lte_lc_pdn_auth_set20lte_lc_pdn_auth_typePKcPKc )

Best regards,

Jannis

[Charlie]

Hi Jannis,

PDN can be set automatically by default or manually, you can search PDN to refer to more discussion about it.

I guess the next step you need to improve your code compatibility with the NB-IoT network.

You can still play nRF9160: Serial LTE modem — nRF Connect SDK 1.9.1 documentation (nordicsemi.com) TCP commands with NB-IoT network and learn its source codes to see how to improve your codes.

Best regards,

Charlie

[jannis]

Thank you! I will look into that

:)