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Dot Development - Migrating to 4.0

Migrating an existing project from Dot libraries v3.3 to v4.0 will require some changes to compile and function properly. The project must use mbed-os 6, the 4.0 libraries are compiled against mbed-os 6.1.0 and are only tested with that version of mbed-os.

This article describes some major changes to the Dot libraries and bootloader in the 4.0 release version that effect project setup and programming. It does not cover changes to LoRa.

Major Changes

  • The Serial class was replaced by UnbufferedSerial and BufferedSerial in mbed-os 6.

  • Device settings on mDot have been migrated from the file system to a separate storage area.

  • External storage support on xDot enabling FOTA.

  • Applications using the 4.0 libraries and mbed-os 6 are not compatible with the bootloader that was automatically included by mbed-os 5.

  • Projects targeting mDot or xDot can now choose to include or exclude a bootloader.

  • New bootloader supports compression and binary difference firmware upgrades.

  • When applying an upgrade the mDot bootloader no longer assumes the file contains a bootloader.

  • A CRC it no longer automatically appended to firmware when compiled with Mbed.

Settings Migration

Settings stored on mDot are migrated automatically when mDot::getInstance is first called. If the new settings area is not found, the mDot loads settings from files lora.cfg, mdot.cfg, and lora.session then erases the entire storage area. Storage is then allocated with 4 sectors allocated to settings and 28 allocated to the file system (a sector is 64KB).

Serial

The Serial class was replaced by UnbufferedSerial and BufferedSerial classes in mbed-os 6. Adding the example code below creates an UnbufferedSerial instance and sets it as the default printf FileHandle.

#include "mbed.h"

...

mbed::UnbufferedSerial debug_port(USBTX, USBRX, LOG_DEFAULT_BAUD_RATE);

FileHandle *mbed::mbed_override_console(int fd)
{
    return &debug_port;
}

...

Bootloader

  • A CRC it no longer automatically appended to firmware when compiled with Mbed.

When upgrading a dot over serial the bootloader uses the appended CRC to verify the received file. Sending a file to a Dot over serial will require calculating and appending a CRC32 to the file before transfering. Multitool can be used to append a CRC and transfer the file.

  • When applying an upgrade the mDot bootloader no longer assumes the file contains a bootloader.

Firmware images sent to the new bootloader must be application only. The old bootloader requires upgrade images to be a merged bootloader and application. Multitool can be used to strip the bootloader from a file.