MQTT simple example code (api based)

RE: MQTT simple example code (api based)

dejans — Fri, 24 Oct 2025 06:53:36 GMT

Hi,

[quote user="dejans"]The modem is doing retransmissions on the TCP (not MQTT) level. I will check internally how many retries there could be and get back to you.[/quote]

TCP has 10 retransmissions, and this is not configurable in the application.

Best regards,
Dejan

RE: MQTT simple example code (api based)

dejans — Thu, 23 Oct 2025 14:41:26 GMT

Hi,

[quote user="sravan.rikka"]1. Assume we have chosen QoS as 1 and our device is publishing data but the broker is down then as per QoS1 theory, when there is no ACK from broker client(device) will retry until get the ACK, how many time nRF9160 modem will retry? Is this retry count is configurable? This retry is handled by stack/library files itself right?(I mean nothing to do in application level)[/quote]

The modem is doing retransmissions on the TCP (not MQTT) level. I will check internally how many retries there could be and get back to you.

[quote user="sravan.rikka"]2. Want to keep nRF9160 in sleep mode and wakeup based on wakeup interrupt, is there any api function to keep in sleep mode? can you share sleep mode example code path in SDK 3.1.0.[/quote]

Modem can be put in low power state by entering PSM or by being turned off. There is lte_lc API for doing this.

[quote user="sravan.rikka"]3. We have subscribe for a topic and got the MQTT_EVT_PUBLISH event when received subscribe data, is this the correct event to check subscribe payload? I am searching for SUBSCIBE event but didn't find it.[/quote]

MQTT_EVT_PUBLISH is publishing event which is received when message is published on a topic client has subscribed to. Payload can be read using mqtt_read_publish_payload().

[quote user="sravan.rikka"]As a code flow first we have to publish payload and then wait for the subscribe data, is this correct? or wait for subscribe data and then publish payload?[/quote]

If device wants to read published payload, it needs to be subscribed beforehand.

Best regards,
Dejan

RE: MQTT simple example code (api based)

sravan.rikka — Tue, 21 Oct 2025 16:54:16 GMT

Hi Dejan,

1. Assume we have chosen QoS as 1 and our device is publishing data but the broker is down then as per QoS1 theory, when there is no ACK from broker client(device) will retry until get the ACK, how many time nRF9160 modem will retry? Is this retry count is configurable? This retry is handled by stack/library files itself right?(I mean nothing to do in application level)

2. Want to keep nRF9160 in sleep mode and wakeup based on wakeup interrupt, is there any api function to keep in sleep mode? can you share sleep mode example code path in SDK 3.1.0.

3. We have subscribe for a topic and got the MQTT_EVT_PUBLISH event when received subscribe data, is this the correct event to check subscribe payload? I am searching for SUBSCIBE event but didn't find it.

As a code flow first we have to publish payload and then wait for the subscribe data, is this correct? or wait for subscribe data and then publish payload?

Regards,

Sravan Rikka

RE: MQTT simple example code (api based)

dejans — Fri, 08 Aug 2025 08:33:00 GMT

Hi,

Have you seen the edit in my previous reply? Can you double-check if the link is turned off in described way?

[quote user="sravan.rikka"]Can you provide modem trace for further analysis? How to get this, please provide procedure.[/quote]

Please have a look at following resources
modem trace
capturing modem trace
snippets for nrf91 series
modem trace module
cellular monitor
capturing modem trace
enable tracing in the application
capturing modem trace using nrfutil

Best regards,
Dejan

RE: MQTT simple example code (api based)

sravan.rikka — Fri, 08 Aug 2025 07:34:14 GMT

Hi Dejan,

Yes, I am using "lte_lc library API".

Can you provide modem trace for further analysis? How to get this, please provide procedure.

Regards,

Sravan Rikka

RE: MQTT simple example code (api based)

dejans — Wed, 06 Aug 2025 13:50:21 GMT

Hi Sravan,

Do you use lte_lc library API in your application?

Can you provide modem trace for further analysis?

EDIT:
You must use lte_lc_deinit to turn off the link if you also use lte_lc to set CFUN=1.

Best regards,
Dejan

RE: MQTT simple example code (api based)

sravan.rikka — Wed, 06 Aug 2025 11:02:32 GMT

Hi Dejan,

I am not making two many calls in an hour, I am making call for every 30minutes, 1st call is successful but second call is not connecting to network. Please suggest how can I resolve this issue.

Regards,

Sravan Rikka

RE: MQTT simple example code (api based)

dejans — Thu, 31 Jul 2025 12:36:42 GMT

Hi,

There is a limitation on a number of connection requests. It could be that you are exceeding number of connection attempts per hour. You can get more information in this discussion.

Best regards,
Dejan

RE: MQTT simple example code (api based)

sravan.rikka — Thu, 31 Jul 2025 05:24:05 GMT

devzone.nordicsemi.com/.../8738.nrf_5F00_log.txt

Hi Dejan,

Please check the attached log.

Regards,

Sravan Rikka

RE: MQTT simple example code (api based)

dejans — Wed, 30 Jul 2025 14:18:09 GMT

Hi,

Can you share complete log that shows the error ""mqtt_simple: Failed to establish LTE connection: -120". (#define EALREADY 120 /* Socket already connected */)."?

Best regards,
Dejan

RE: MQTT simple example code (api based)

sravan.rikka — Wed, 30 Jul 2025 12:38:43 GMT

Hi Dejan,

Thank you for the support to resolving float value issue.

I have added CONFIG_NEWLIB_LIBC_FLOAT_PRINTF=y in the .prj as you suggested, now I can see the float values in the buffer.

Queries:

1. I am connecting to the network only at power ON and making continuous calls for every 30min to the MQTT broker successfully. Now I am implementing that connect to the network and publish the data then disconnect from the network for every call. Hence, I have implemented socket close as below and got response as 'ret=0' for "ret = zsock_close(socketfd);" but when I connect to the network again for the second call getting error as "mqtt_simple: Failed to establish LTE connection: -120". (#define EALREADY 120 /* Socket already connected */).

Can you suggest, how to resolve this issue.

function()

{

err = mqtt_disconnect(&client);
k_sleep(K_MSEC(2000u));
printk("mqtt_disconnect:%d\n", err);
current_state = STATE_EXIT;

k_sleep(K_MSEC(200u));

close_socket();

}

void close_socket(void)
{
int err;
int socketfd = 0;

int ret;

socketfd = zsock_socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP);
ret = zsock_close(socketfd);

printk("zsock_close:%d\r\n", ret);

err = at_cmd_write(AT_CFUN_OFF_RADIO_CMD, NULL, 0, NULL);
k_sleep(K_MSEC(20u));
if(err < 0)
printk("Failed AT_CFUN_OFF_RADIO_CMD\r\n");
else
printk("Success AT_CFUN_OFF_RADIO_CMD\r\n");
}

Regards,

Sravan Rikka

RE: MQTT simple example code (api based)

dejans — Wed, 23 Jul 2025 11:48:39 GMT

Hi Sravan,

I have tested in NCS v3.0.2, not in NCS v1.7.0. I am sorry that I forgot to mention this. In your case, it should be correct to use #include <sys/printk.h> instead of
#include <zephyr/sys/printk.h>.
You could try to use Newlib. You can look at types of Newlib and its formatted output.

Best regards,
Dejan

RE: MQTT simple example code (api based)

sravan.rikka — Tue, 22 Jul 2025 12:37:45 GMT

Hi Dejan,

I have added #include <zephyr/sys/printk.h> but got compilation error as "zephyr/sys/printk.h: No such file or directory". then searched for printk.h and found that it was added like #include <sys/printk.h> and added same and no compilation error but still not seeing float values in snprintf buffer.

Tried adding CONFIG_PICOLIBC=y and CONFIG_PICOLIBC_IO_FLOAT=y in .prj but code is not loading after adding these configuration, after removing able to load code. So, unable to add these to config, is there any other way to add it? please guide and help to resolve this issue.

Regards,

Sravan Rikka

RE: MQTT simple example code (api based)

dejans — Wed, 16 Jul 2025 10:11:04 GMT

Hi Sravan,

You can try to add this header file

#include <zephyr/sys/printk.h>

and these Kconfig options

CONFIG_PICOLIBC=y
CONFIG_PICOLIBC_IO_FLOAT=y

Best regards,
Dejan

RE: MQTT simple example code (api based)

sravan.rikka — Tue, 15 Jul 2025 16:51:36 GMT

Hi Dejan,

1. Not yet, I will check broker side limitations.

2. For me it is not working, I am using 'mqtt simple' example code. Please suggest me how to resolve this. Below are the header files in the main file. Do we need to add any other header file?

#include <zephyr.h>
#include <stdio.h>
#include <drivers/uart.h>
#include <string.h>
#include <random/rand32.h>
#include <net/mqtt.h>
#include <net/socket.h>
#include <modem/at_cmd.h>
#include <modem/lte_lc.h>
#include <logging/log.h>
#if defined(CONFIG_MODEM_KEY_MGMT)
#include <modem/modem_key_mgmt.h>
#endif
#if defined(CONFIG_LWM2M_CARRIER)
#include <lwm2m_carrier.h>
#endif
#include <dk_buttons_and_leds.h>

#include "certificates.h"

Regards,

Sravan Rikka

RE: MQTT simple example code (api based)

dejans — Tue, 15 Jul 2025 08:32:17 GMT

Hi Sravan,

[quote user="sravan.rikka"]1. In our application we will store 5000 records and each record of size 1429, hence total bytes=5000 * 1429=7145000. Hence, we are planning to transfer 7.145MB in single MQTT publish. It is possible right?[/quote]

Have you checked if there are any limitations on the broker side?

[quote user="sravan.rikka"]

2. When I am copying float value into buf using sprintf I am not seeing any value in the buffer, why? whereas %d is working but %f is not working. Am I missing anything, please advice.

float ambientTemperature = 24.5;
len = snprintf(buf, sizeof(buf), "ambientTemperature=%f", ambientTemperature);
printk(buf);

[/quote]

I have used the following sample which correctly displays ambientTemperature value from the buffer buf.

#include <stdio.h>

char buf[200];
int len;

int main(void)
{
    float ambientTemperature = 24.5;
    len = snprintf(buf, sizeof(buf), "ambientTemperature=%f", ambientTemperature);
    printf("buffer value is %s", buf);
}

Best regards,
Dejan

RE: MQTT simple example code (api based)

sravan.rikka — Mon, 14 Jul 2025 11:52:55 GMT

Hi Dejan,

Please respond to below queries I am waiting for your responses. Thank you.

1. In our application we will store 5000 records and each record of size 1429, hence total bytes=5000 * 1429=7145000. Hence, we are planning to transfer 7.145MB in single MQTT publish. It is possible right?

2. When I am copying float value into buf using sprintf I am not seeing any value in the buffer, why? whereas %d is working but %f is not working. Am I missing anything, please advice.

float ambientTemperature = 24.5;
len = snprintf(buf, sizeof(buf), "ambientTemperature=%f", ambientTemperature);
printk(buf);

Regards,

Sravan Rikka

RE: MQTT simple example code (api based)

sravan.rikka — Mon, 14 Jul 2025 09:38:03 GMT

Hi Dejan,

I am using tago.io broker.

I am saying that snprintf itself not copying the float value into buffer when I use %f.

Regards,

Sravan Rikka

RE: MQTT simple example code (api based)

dejans — Mon, 14 Jul 2025 09:07:25 GMT

Hi Sravan,

Which MQTT broker do you use?

If you use picolib, ensure that PICOLIB_IO_FLOAT is enabled.

Best regards,
Dejan

RE: MQTT simple example code (api based)

sravan.rikka — Mon, 14 Jul 2025 08:59:11 GMT

Hi Dejan,

Can you please respond to above queries.

Regards,

Sravan Rikka

RE: MQTT simple example code (api based)

sravan.rikka — Fri, 11 Jul 2025 11:11:52 GMT

Hi Dejan,

2. When I am copying float value into buf using sprintf I am not seeing any value in the buffer, why? whereas %d is working but %f is not working. Am I missing anything, please advice.

float ambientTemperature = 24.5;
len = snprintf(buf, sizeof(buf), "ambientTemperature=%f", ambientTemperature);
printk(buf);

Regards,

Sravan Rikka

RE: MQTT simple example code (api based)

dejans — Thu, 10 Jul 2025 13:56:40 GMT

Hi Sravan,

The size of MQTT publish message is not limited by the modem. Can you provide details about your setup?

Immutable bootloader cannot be altered or deleted without erasing whole device.

Best regards,
Dejan

RE: MQTT simple example code (api based)

sravan.rikka — Thu, 10 Jul 2025 12:30:00 GMT

Hi Dejan,

I think MQTT specification says max publish size is 256MB. We can publish maximum 256MB in single publish, am I correct?

I want o send 100MB of data, can I increase below message buffer size to 100MB?

#define CONFIG_MQTT_MESSAGE_BUFFER_SIZE 100MB

is this "secure immutable bootloader" available for us to add some piece of code in it?

Regards,

Sravan Rikka

RE: MQTT simple example code (api based)

dejans — Thu, 10 Jul 2025 12:13:35 GMT

Hi Sravan,

There is no PUBLISH MQTT message limitation in your case and any amount of data can be sent. You can try to increase message buffer size if needed.

There is no boot ROM but there is nRF Secure Immutable Bootloader.

Best regards,
Dejan

RE: MQTT simple example code (api based)

sravan.rikka — Thu, 10 Jul 2025 09:08:42 GMT

Hi Dejans,

For my 1 and 2 queries:

I have looked at your suggested links and it is talking about TLS but I am not using TLS, I am using nonsecure MQTT.

For non-secure MQTT also 2KB is the limit in single publish?

In MQTT simple code I can see tx_buffer and rx_buffer size as 128 bytes, can I make it to 2048 bytes? This is the correct place to increase the MQTT publish buffer size or is there any other place need to change?

#define CONFIG_MQTT_MESSAGE_BUFFER_SIZE 128
#define CONFIG_MQTT_PAYLOAD_BUFFER_SIZE 128

/* Buffers for MQTT client. */
static uint8_t rx_buffer[CONFIG_MQTT_MESSAGE_BUFFER_SIZE];
static uint8_t tx_buffer[CONFIG_MQTT_MESSAGE_BUFFER_SIZE];

Regards,

Sravan Rikka