nRF9160 TCP connection, sending over LTE-M

RE: nRF9160 TCP connection, sending over LTE-M

newUser — Tue, 01 Sep 2020 14:28:49 GMT

We are now successfully communicating with our own server. Thank you for your support and patience.

RE: nRF9160 TCP connection, sending over LTE-M

newUser — Tue, 01 Sep 2020 12:10:23 GMT

Øyvind Thank you guys. I can also confirm that the U-Blox test server is no longer working according to their spec.

I will setup our own server again and report back the latest results, perhaps the code is already working.

RE: nRF9160 TCP connection, sending over LTE-M

newUser — Tue, 01 Sep 2020 08:51:49 GMT

Hi, no problem! Thank you for getting back to me.

The current status is that with UDP, everything works fine. With TCP, the server's welcome message is received, but after that no communication is working anymore. The send() function still returns 0 (success) and the expected number of written bytes (13), but the recv() fails (we would expected the 'Hello U-Blox' message to be echoed):

Sent: AT+CFUN=1
Received: OK

tcp_socket: 2
connect to 195.34.89.241 err: 0
Received: U-Blox AG TCP/UDP test service
 [31]
Sent: Hello U-Blox [Bytes: 13] [Error: 0]
Receive failed: [Bytes: 0] [Error: 0]
Send failed: 54
Receive failed: [Bytes: -1] [Error: 54]

When I test this server with other embedded devices, it is working just fine for both UDP and TCP.
Our own remote management server is also working just fine with these other devices, but we observe the above behavior when connecting from the nRF9160 board.

The code producing this output:

#include <zephyr.h>
#include <device.h>
#include <drivers/gpio.h>

#include <stdint.h>

#include <net/socket.h>

#include "test.h"

#define TEST_THREAD_PRIORITY 7

#define TCP_HOST "195.34.89.241"
#define TCP_PORT 7
#define RECV_BUF_SIZE 128

static uint8_t recv_buf[RECV_BUF_SIZE];

K_THREAD_STACK_DEFINE(testThreadStack, 2048);
struct k_thread testThread;

static void TestThreadFxn (void);

void TestCreateThread (void)
{
  k_thread_create(&testThread, testThreadStack,
                  K_THREAD_STACK_SIZEOF(testThreadStack),
                  (k_thread_entry_t) TestThreadFxn,
                  NULL, NULL, NULL,
                  TEST_THREAD_PRIORITY, 0, K_NO_WAIT);
}

static void TestThreadFxn (void)
{
  printk("Starting socket\n");

  int at_socket_fd = socket(AF_LTE, SOCK_DGRAM, NPROTO_AT);

  if (at_socket_fd < 0)
  {
    printk("Socket err: %d, errno: %d\r\n", at_socket_fd, errno);
  }

  char *initCmds[1] = { "AT+CFUN=1" };
  send(at_socket_fd, initCmds[0], strlen(initCmds[0]), 0);
  printk("Sent: %s\n", initCmds[0]);

  recv(at_socket_fd, recv_buf, sizeof(recv_buf), 0);
  printk("Received: %s\n", recv_buf);

  k_msleep(20000);

  int tcp_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP); // SOCK_DGRAM, IPPROTO_UDP
  printk("tcp_socket: %i\n", tcp_socket);

  struct sockaddr_in remote_addr;
  remote_addr.sin_family = AF_INET;
  remote_addr.sin_port = htons(TCP_PORT);
  inet_pton(AF_INET, TCP_HOST, &(remote_addr.sin_addr));

  int err = connect(tcp_socket, (struct sockaddr *) &remote_addr, sizeof(remote_addr));
  printk("connect to %s err: %i\n", TCP_HOST, err);

  int bytes_received = recv(tcp_socket, recv_buf, sizeof(recv_buf), 0);
  if (bytes_received > 0)
  {
    printk("Received: %s [%i]\n", recv_buf, bytes_received);
  }
  else
  {
    printk("Receive failed: %i\n", errno);
  }

  for (;;)
  {
    memset(recv_buf, 0, sizeof(recv_buf));

    uint8_t cmd[] = "Hello U-Blox";

    int bytes_sent = send(tcp_socket, cmd, sizeof(cmd), 0);
    if (bytes_sent < 0)
    {
      printk("Send failed: %i\n", errno);
    }
    else
    {
      printk("Sent: %s [Bytes: %i] [Error: %i]\n", cmd, bytes_sent, errno);
    }

    int bytes_received = recv(tcp_socket, recv_buf, sizeof(recv_buf), 0);
    if (bytes_received > 0)
    {
      printk("Received: %s [Bytes: %i]\n", recv_buf, bytes_received);
    }
    else
    {
      printk("Receive failed: [Bytes: %i] [Error: %i]\n", bytes_received, errno);
    }

    k_msleep(5000);
  }
}

proj.conf:

#
# Copyright (c) 2019 Nordic Semiconductor ASA
#
# SPDX-License-Identifier: LicenseRef-BSD-5-Clause-Nordic
#
# General config
CONFIG_ASSERT=y

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

# BSD library
CONFIG_BSD_LIBRARY=y

# AT host library
CONFIG_AT_HOST_LIBRARY=y
CONFIG_UART_INTERRUPT_DRIVEN=y

# Stacks and heaps
CONFIG_MAIN_STACK_SIZE=4096
CONFIG_HEAP_MEM_POOL_SIZE=32768

# Testing changes
CONFIG_GPIO=y

RE: nRF9160 TCP connection, sending over LTE-M

Øyvind — Tue, 01 Sep 2020 08:19:20 GMT

Hello,

My apologies for the late reply. Difficult to see what you have altered in the main post, it's better to add changes as a comment to the thread. Can you please add prj.conf and main.c ?

[quote user="MaikASB"]ECONNRESET "Connection reset by peer":[/quote]

A connection reset by peer message means that the site you are connected to has reset the connection. This is usually caused by a high amount of traffic on the site, but may be caused by a server error as well.

What other servers did you try?

RE: nRF9160 TCP connection, sending over LTE-M

newUser — Thu, 27 Aug 2020 09:37:15 GMT

Øyvind I have edited the main post. I would appreciate your input!

RE: nRF9160 TCP connection, sending over LTE-M

newUser — Fri, 21 Aug 2020 11:54:43 GMT

I also tested UDP. This seems to work just fine. Funny thing though is, send() is returning 0 here as well. But the data is being echoed.

TCP is still not working. I disabled power saving to make sure that nothing funny is happening there:

AT+CEPPI=0
AT+CPSMS=0
AT+CEDRXS=0

The socket seems to just get closed after receiving the initial data, resulting in error code ECONNRESET "Connection reset by peer":

tcp_socket: 2
connect to 195.34.89.241 err: 0
Received: U-Blox AG TCP/UDP test service
 [31]
Sent: Hello U-Blox [0]
// -------------------------> Here there is a pause
+CSCON: 0
+CSCON: 1
Receive failed: 0
Send failed: 54
Receive failed: 54

I have also tried it with another server, same thing happens. Both servers are proven to work correctly when connecting from other devices.

RE: nRF9160 TCP connection, sending over LTE-M

newUser — Fri, 21 Aug 2020 10:11:28 GMT

Hi,

I'm using NCS 1.3.0.
Upon further investigation, the send() function returns 0, indicating no error, but still 0 bytes transmitted.

I believe this means the socket is closed. Perhaps I should change modem / connection / socket options?
Other connections from both my PC and another embedded device (other modem) do not have this problem.

RE: nRF9160 TCP connection, sending over LTE-M

Øyvind — Fri, 21 Aug 2020 09:50:46 GMT

Hello,

What version of NCS are you using? It looks like the server is the issue here as it doesn't echo back. Attached is the main.c used in coap_client with added error handling just rename replace with main.c in the coap_client sample and rename to main.c
devzone.nordicsemi.com/.../main_5F00_dz255052.c

Please see this list with possible issues given by errno -1.

Kind regards,
Øyvind