Keeping the MKR1500 modem on during idle state

[dkanday]

Hi,

I am trying to use MQTT broker for connecting the Arduino MKR NB 1500 to receive and send data from the webpage. I have set the modem to publish the data once every min, which causes the modem to go to sleep state. This causes the subscribed message to be delayed by 15-20 seconds after it was sent from the webpage.
Is there an AT command which I could use to keep the modem always on? power consumption is not an issue for me and neither is the data limit. The end goal is I want to only to publish the message when there is a change in the ADC value and immediately subscribe to the data when it is being transmitted by the webpage/server.
Below is the code I am using

#include <ArduinoBearSSL.h>
#include <ArduinoECCX08.h>
#include <utility/ECCX08SelfSignedCert.h>
#include <ArduinoMqttClient.h>
#include <MKRNB.h>

#include "arduino_secrets.h"
int sensorValue;
int length;

/////// Enter your sensitive data in arduino_secrets.h
const char pinnumber[]   = SECRET_PINNUMBER;
const char broker[]      = SECRET_BROKER;
String     deviceId      = SECRET_DEVICE_ID;

NB nbAccess;
GPRS gprs;

NBClient      nbClient;            // Used for the TCP socket connection
BearSSLClient sslClient(nbClient); // Used for SSL/TLS connection, integrates with ECC508
MqttClient    mqttClient(sslClient);

unsigned long lastMillis = 0;

void setup() {
  Serial.begin(9600);
  while (!Serial);

  if (!ECCX08.begin()) {
    Serial.println("No ECCX08 present!");
    while (1);
  }

  // reconstruct the self signed cert
  ECCX08SelfSignedCert.beginReconstruction(0, 8);
  ECCX08SelfSignedCert.setCommonName(ECCX08.serialNumber());
  ECCX08SelfSignedCert.endReconstruction();

  // Set a callback to get the current time
  // used to validate the servers certificate
  ArduinoBearSSL.onGetTime(getTime);

  // Set the ECCX08 slot to use for the private key
  // and the accompanying public certificate for it
  sslClient.setEccSlot(0, ECCX08SelfSignedCert.bytes(), ECCX08SelfSignedCert.length());

  // Set the client id used for MQTT as the device id
  mqttClient.setId(deviceId);

  // Set the username to "<broker>/<device id>/api-version=2018-06-30" and empty password
  String username;

  username += broker;
  username += "/";
  username += deviceId;
  username += "/api-version=2018-06-30";

  mqttClient.setUsernamePassword(username, "");

  // Set the message callback, this function is
  // called when the MQTTClient receives a message
  mqttClient.onMessage(onMessageReceived);
}

void loop() {
  if (nbAccess.status() != NB_READY || gprs.status() != GPRS_READY) {
    connectNB();
  }

  if (!mqttClient.connected()) {
    // MQTT client is disconnected, connect
    connectMQTT();
  }

  // poll for new MQTT messages and send keep alives
  mqttClient.poll();

  // publish a message roughly every 5 seconds.
  if (millis() - lastMillis > 5000) {
    lastMillis = millis();

    publishMessage();
  }
}

unsigned long getTime() {
  // get the current time from the cellular module
  return nbAccess.getTime();
}

void connectNB() {
  Serial.println("Attempting to connect to the cellular network");

  while ((nbAccess.begin(pinnumber) != NB_READY) ||
         (gprs.attachGPRS() != GPRS_READY)) {
    // failed, retry
    Serial.print(".");
    delay(1000);
  }

  Serial.println("You're connected to the cellular network");
  Serial.println();
}

void connectMQTT() {
  Serial.print("Attempting to MQTT broker: ");
  Serial.print(broker);
  Serial.println(" ");

  while (!mqttClient.connect(broker, 8883)) {
    // failed, retry
    Serial.print(".");
    Serial.println(mqttClient.connectError());
    delay(5000);
  }
  Serial.println();

  Serial.println("You're connected to the MQTT broker");
  Serial.println();

  // subscribe to a topic
  mqttClient.subscribe("devices/" + deviceId + "/messages/devicebound/#");
}

void publishMessage() {
  Serial.println("Publishing message");

  // send message, the Print interface can be used to set the message contents
  mqttClient.beginMessage("devices/" + deviceId + "/messages/events/");
  mqttClient.print("hello ");
  sensorValue = analogRead(A0);
  mqttClient.println(sensorValue);
  //mqttClient.print(millis());
  
  mqttClient.endMessage();
}

void onMessageReceived(int messageSize) {
  // we received a message, print out the topic and contents
  Serial.print("Received a message with topic '");
  Serial.print(mqttClient.messageTopic());
  Serial.print("', length ");
  Serial.print(messageSize);
  Serial.println(" bytes:");

  // use the Stream interface to print the contents
  while (mqttClient.available()) {
    Serial.print((char)mqttClient.read());

}
    
  Serial.println();

  Serial.println();
}