Blues Wireless has announced the developer beta of Outboard DFU for over-the-air host firmware updates.

As of Notecard firmware v3.5.1, the Notecard can perform a host firmware update from the outside without involving the firmware running on the MCU. Firmware can be updated regardless of RTOS or language. Users can switch between them, even modify flash memory layout and partition any time after the fact.

The company is inviting users to check out the capabilities of Outboard DFU as it is supported on numerous ESP32, STM32 and nRF chips; a comprehensive list is coming soon. Those looking for a turnkey option can try Outboard DFU with the Notecarrier-F and Adafruit STM32F405 Feather Express or Blues Wireless Swan 3.0.

An increasing number of MCUs produced in the last decade are shipped with their primary bootloaders in ROM, unmodifiable by any user operation. On these devices, including all modern ST Microelectronics and Espressif microcontrollers, when a reset pin is asserted, the device enters this ROM bootloader.

The bootloader can load and execute code from various sources including flash, RAM, uart, USB, I²C or SPI. This ROM bootloader’s behaviour is controlled by actively probing those IO ports and by sampling the state of strapping pins or specially locked boot option bytes in flash.

These manufacturer-provided ROM bootloaders present alternatives for hardware designers, specifically to perform firmware updates in a manner that is more flexible in terms of language and RTOS, and less vulnerable to inadvertent programming bugs.

Beginning with firmware version 3.5.1, the Blues Wireless Notecard is now capable of using these capabilities of modern MCUs, performing firmware updates from the outside and not involving the firmware running on the MCU whatsoever. It can update firmware regardless of RTOS or language, and can be used to switch between them, even modifying flash memory layout and partitioning any time after the fact, at the developer’s choice.

Taking advantage of these capabilities requires that the hardware designer lay out several connections between the Notecard’s aux pins and the host MCU’s reset, boot and uart pins. By using the Notecard with a modern MCU with a ROM bootloader, it can achieve a more robust form of firmware update that Blues calls Outboard DFU.

Today this wiring is available out-of-the-box and supported in the Notecarrier-F when used with one of its tested Outboard DFU MCUs.