MQTT simple example code (api based)

[sravan.rikka]

Hi Team,

We are using nRF9160 MQTT sample code 'mqtt_simple'. 

1. What is the maximum payload we can send in one single PUBLISH?

2. I want to send 4KB of data in single PUBLISH, is this possible? if not, what is the way to send 4KB in single PUBLISH?

3. Is the nRF9160 supports secure boot?

4. Is the nRF9160 has boot ROM? If yes, is this boot ROM available for us to add some piece of code in the boot ROM?

Regards,

Sravan Rikka

[dejans]

Hi,

1. What is the maximum payload we can send in one single PUBLISH?

2. I want to send 4KB of data in single PUBLISH, is this possible? if not, what is the way to send 4KB in single PUBLISH?

There is a data communication limit in modem due to max size of TLS buffer of 2 KB. You can read about the limit  in the documentation. Furthermore, you can look at MQTT sample overview and this discussion. For sending larger messages, you can split your big MQTT message into smaller ones.

3. Is the nRF9160 supports secure boot?

Yes, you can look at features and nRF91 security features.

4. Is the nRF9160 has boot ROM? If yes, is this boot ROM available for us to add some piece of code in the boot ROM?

I will check this internally.

Best regards,
Deja

[sravan.rikka]

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

[dejans]

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

[sravan.rikka]

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

[dejans]

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

[sravan.rikka]

Hi Dejan,

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

[sravan.rikka]

Hi Dejan,

Can you please respond to above queries.

Regards,

Sravan Rikka

[dejans]

Hi Sravan,

Which MQTT broker do you use?

If you use picolib, ensure that PICOLIB_IO_FLOAT is enabled.

Best regards,
Dejan

[sravan.rikka]

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

[sravan.rikka]

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

[dejans]

Hi Sravan,

sravan.rikka said:

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?

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

sravan.rikka said:

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);

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

[sravan.rikka]

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