Overview#

The Silicon Labs Gecko Bootloader is a common bootloader for all the newer MCUs and wireless MCUs from Silicon Labs. The Gecko Bootloader can be configured to perform a variety of bootload functions, from device initialization to firmware upgrades. The Gecko Bootloader uses a proprietary format for its upgrade images, called GBL (Gecko Bootloader). These images are produced with the file extension ".gbl". Additional information on the GBL file format is provided in UG103.6: Bootloader Fundamentals.

On EFR32 Series 1 devices, the Gecko Bootloader has a two-stage design, first stage and main stage, where a minimal first stage bootloader is used to upgrade the main bootloader. The first stage bootloader only contains functionality to read from and write to fixed addresses in internal flash. To perform a main bootloader upgrade, the running main bootloader verifies the integrity and authenticity of the bootloader upgrade image file. The running main bootloader then writes the upgrade image to a fixed location in internal flash and issues a reboot into the first stage bootloader. The first stage bootloader verifies the integrity of the main bootloader firmware upgrade image by computing a CRC32 checksum, before copying the upgrade image to the main bootloader location.

On EFR32 Series 2 devices, the Gecko bootloader consists only of the main stage bootloader. The main bootloader is upgradable through the hardware peripheral Secure Element. The Secure Element provides functionality to install an image to address 0x0 in internal flash, by copying from a configurable location in internal flash. To perform a main bootloader upgrade, the running main bootloader verifies the integrity and authenticity of the bootloader upgrade image file. The running main bootloader then writes the upgrade image to the upgrade location in flash and requests that the Secure Element installs it. On some devices, the Secure Element is also capable of verifying the authenticity of the main bootloader upgrade image against a root of trust. The Secure Element itself is upgradable using the same mechanism. More details are provided in UG266: Silicon Labs Gecko Bootloader User’s Guide.

The Gecko Bootloader can be configured to perform firmware upgrades in standalone mode (also called a standalone bootloader) or in application mode (also called an application bootloader), depending on the component configuration. Components can be enabled and configured through the Simplicity Studio IDE.

Note: Zigbee EmberZNet SDK 7.0 introduced a new component-based architecture, along with a Project Configurator and other tools to replace AppBuilder and plugin configuration. In general, the new software components are comparable to the old plugins. Unless otherwise specified, the term 'component' should be understood to refer to the corresponding plugin, if you are working in SDK 6.10.x or lower. For more information, see AN1301: Transitioning from Zigbee EmberZNet SDK 6.x to SDK 7.x.

A standalone bootloader uses a communications channel to get a firmware upgrade image. NCP (network co-processor) devices always use standalone bootloaders. Standalone bootloaders perform firmware image upgrades in a single-stage process that allows the application image to be placed into flash memory, overwriting the existing application image, without the participation of the application itself. In general, the only time that the application interacts with a standalone bootloader is when it requests to reboot into the bootloader. Once the bootloader is running, it receives packets containing the firmware upgrade image by a physical connection such as UART or SPI. To function as a standalone bootloader, a component providing a communication interface such as UART or SPI must be configured.

An application bootloader relies on the application to acquire the firmware upgrade image. The application bootloader performs a firmware image upgrade by reprogramming the device’s flash with the firmware upgrade image stored in a region of flash memory referred to as the download space. The application transfers the firmware upgrade image to the download space in any way that is convenient (UART, over-the-air, and so on). The download space is either an external memory device such as an EEPROM or dataflash or a section of the chip’s internal flash. The Gecko Bootloader can partition the download space into multiple storage slots, and store multiple firmware upgrade images simultaneously. To function as an application bootloader, a component providing a bootloader storage implementation has to be configured.

This document describes how to use both models with Zigbee EmberZNet.