Is it possible to implement MQTT on this device?
Any device that has TCP/IP layer can implement MQTT.
What requirements should a microcontroller match to be able to use/run MQTT?
You need to ask the following questions to know whether your device runs MQTT.
Is my device having TCP/IP or networking support?
Is there some memory and disk space available ...
The mbed mmqt library doesn't seem to document any memory requirements as likely to be limiting, and can reasonably be assumed to be targetted at this sort of small-footprint device as an endpoint. You could fairly trivially import the library into a similar device platform using the online compiler and check the code footprint at least.
My guess is that this is a power-supply related at some level. Either the external supply, or on-board switching of power rails.
To clarify the scenario, debug works fine after a hardware reset, but when your target erases a block of flash, the debug connection is dropped?
Debug doesn't care about code running correctly - you can be in lockup state, and ...
You might want to check out Amazon FreeRTOS.
Amazon FreeRTOS (a:FreeRTOS) is an operating system for microcontrollers that makes small, low-power edge devices easy to program, deploy, secure, connect, and manage. Amazon FreeRTOS is based on the FreeRTOS kernel, a popular open source operating system for microcontrollers, and extends it with software ...
AWS IOT requires that your device understand TCP/IP and encryption.
The ATMega328 has 2K bytes of RAM, but Ethernet frames can be up to 1500 bytes long. Even if you could receive a packet, there wouldn't be any room left to process it.
The nRF51822 has 16K RAM, which is plenty for Ethernet, but not enough to do TCP/IP and WiFi. (Both of which require ...
If your application is running from battery, you should probably choose BLE. Any other requirements could be fulfilled with both WiFi or Bluetooth. You could connect to a mobile app either via WiFi or Bluetooth as well.
As for the STM32 there are very convenient Bluetooth and WiFi modules out there that you could hook up on an UART to the STM32 and control ...