First and second transmission fails in nRF9160

[Yusuke]

hardware: nRF9160 DK 0.8.2
firmware: 0.7.0-29.alpha

I want to send data every a few seconds through MQTT. It fails in the first and second Tx after MQTT client initiation, and succeeds after that. It releases error = -57.
Why does it fails in the first and second Tx after initiation?

I tested the code below. I added four lines to mqtt_simple.
mqtt_simple: https://github.com/NordicPlayground/fw-nrfconnect-nrf/blob/master/samples/nrf9160/mqtt_simple/src/main.c

<main.c>

.
.
.
void main(void)
{
	int err;

	printk("The MQTT simple sample started\n");

	modem_configure();

	client_init(&client);

	err = mqtt_connect(&client);
	if (err != 0) {
		printk("ERROR: mqtt_connect %d\n", err);
		return;
	}

	err = fds_init(&client);
	if (err != 0) {
		printk("ERROR: fds_init %d\n", err);
		return;
	}

        k_sleep(20*1000); // ADD HERE
        err = data_publish(&client, MQTT_QOS_0_AT_MOST_ONCE, "a", strlen("a"));  // ADD HERE
        printk("err=%d\n", err); // ADD HERE
        printk("Send reset message\n"); // ADD HERE

	while (1) {
.
.
.

and the result is here. err=-57

***** Booting Zephyr OS v1.14.99-ncs1 *****
The MQTT simple sample started
LTE Link Connecting ...
LTE Link Connected!
IPv4 Address found 0x????????
Publishing: a
to topic: myPubTopic len: 10
err=-57
Send reset message
mqtt_input start
[mqtt_evt_handler:168] MQTT client connected!
Subscribing to: mySubTopic len 10
mqtt_input end
mqtt_input start
[mqtt_evt_handler:218] SUBACK packet id: 1234
mqtt_input end

Any advice?

[AndreasF]

Hi again.

It is working for me now, but I moved data_publish() to the connection event in the event handler, MQTT_EVT_CONNACK.

The issue was probably that you tried to publish data without being in the connection state.

Best regards,

Andreas

[Yusuke]

OK. I figured out. mqtt_connect does not deal with CONNACK so that you need to poll after mqtt_connect.

void main(void)
{
	int err;

	printk("The MQTT simple sample started\n");

	modem_configure();

	client_init(&client);

	err = mqtt_connect(&client);
	if (err != 0) {
		printk("ERROR: mqtt_connect %d\n", err);
		return;
	}

	err = fds_init(&client);
	if (err != 0) {
		printk("ERROR: fds_init %d\n", err);
		return;
	}

    err = poll(&fds, 1, K_SECONDS(CONFIG_MQTT_KEEPALIVE)); 
    if (err < 0) {
            printk("ERROR: poll %d\n", errno);
    }

    if ((fds.revents & POLLIN) == POLLIN) {
            err = mqtt_input(&client);
            if (err != 0) {
                    printk("ERROR: mqtt_input %d\n", err);
            }
    }

    while(1){
            err = data_publish(&client, MQTT_QOS_0_AT_MOST_ONCE, "a", strlen("a")); // This works out
            printk("err=%d\n", err);
            printk("Send reset message\n");
            k_sleep(2*1000);
    }
}

[dtquang89]

This helps me. Thank you a lot.