Mqtt notes

Notes on MQTT

Looks like in Nordic Semi's aws_iot sample app, the following enumerated events represent a firmware instance receiving subscribed messages from an MQTT broker:

- 1108 DEV - aws_iot event handler called,
AWS_IOT_EVT_READY
- 1108 DEV - aws_iot event handler called,
AWS_IOT_EVT_DATA_RECEIVED

s3://iot-poc/hello/world/

Ah, trouble when attempting to add MQTT topics:

*** Booting Zephyr OS build v2.6.0-rc1-ncs1  ***
I: Modem library is not yet initialized, AT commands not sent
I: Configuration of MAGPIO and COEX0 is left to drivers
The AWS IoT sample started, version: v1.0.0
ZZZ
ZZZ
ZZZ
ZZZ - preparing to subscribe to hello/world topic,
ZZZ
ZZZ
ZZZ - calling routine to subscribe to MQTT topics . . .
ZZZ
E: Application subscription list count mismatch
aws_iot_subscription_topics_add, error: -122
ZZZ
ZZZ
ZZZ
ZZZ
Adding application specific topics failed, error: -122
Summary of callback pointers for 'set flag' events:

Appears to come from `./nrf/subsys/net/lib/aws_iot/src/aws_iot.c:1168: LOG_ERR("Application subscription list count mismatch");`

Note 3 - code excert from `nrf/subsys/net/lib/aws_iot/src/aws_iot.c`:

 689                 if (!mqtt_evt->param.connack.session_present_flag ||
 690                     IS_ENABLED(CONFIG_MQTT_CLEAN_SESSION)) {
 691                         err = topic_subscribe();
 692 
 693                         if (err < 0) {
 694                                 aws_iot_evt.type = AWS_IOT_EVT_ERROR;
 695                                 aws_iot_evt.data.err = err;
 696                                 aws_iot_notify_event(&aws_iot_evt);
 697                                 break;
 698                         }
 699                         if (err == 0) {
 700                                 /* There were not topics to subscribe to. */
 701                                 aws_iot_evt.type = AWS_IOT_EVT_READY;
 702                                 aws_iot_notify_event(&aws_iot_evt);
 703                         } /* else: wait for SUBACK */
 704                 } else {
 705                         /* pre-existing session:
 706                          * subscription is already established.
 707                          */
 708                         aws_iot_evt.type = AWS_IOT_EVT_READY;
 709                         aws_iot_notify_event(&aws_iot_evt);
 710 
 711                         if (IS_ENABLED(

A link to review:

• https://thenewstack.io/mqtt-protocol-iot/

2021-12-14 Tue

• https://forums.aws.amazon.com/index.jspa
• https://aws.amazon.com/blogs/iot/getting-started-mqtt-retained-messages-aws-iot-core/
• https://docs.aws.amazon.com/iot/latest/developerguide/mqtt.html#mqtt-retain

2021-12-08

*  https://github.com/aws/aws-iot-device-sdk-embedded-C/blob/main/demos/mqtt/mqtt_demo_basic_tls/mqtt_demo_basic_tls.c

+++

*  https://docs.aws.amazon.com/iot/latest/developerguide/topics.html

Unsorted references to MQTT:

# https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/zephyr/samples/net/mqtt_publisher/README.html
# https://www.hivemq.com/blog/mqtt-essentials-part2-publish-subscribe/
# https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/zephyr/samples/index.html
# https://www.circuito.io/blog/arduino-code/
# https://www.hivemq.com/blog/mqtt-essentials-part-7-persistent-session-queuing-messages/
# https://www.hivemq.com/blog/mqtt-essentials-part-3-client-broker-connection-establishment/

# https://developer.nordicsemi.com/nRF_Connect_SDK/doc/1.6.1/nrf/examples.html
# https://developer.nordicsemi.com/nRF_Connect_SDK/doc/1.6.1/nrf/ug_tfm.html#ug-tfm
# https://ci-builds.trustedfirmware.org/static-files/UxIoKYsDyPQ0ojvJOv9EX6-hZNDZd6IPGfcm05Bk1b0xNjM3MTA4NjMxODUxOjk6YW5vbnltb3VzOmpvYi90Zi1tLWJ1aWxkLWRvY3MtbmlnaHRseS9sYXN0U3RhYmxlQnVpbGQvYXJ0aWZhY3Q=/trusted-firmware-m/build/docs/user_guide/html/index.html

Nordic AWS FOTA example:

# https://developer.nordicsemi.com/nRF_Connect_SDK/doc/1.6.1/nrf/samples/nrf9160/aws_fota/README.html