OTA bootloader service description

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DocID026293 Rev 2

Figure 2: BLE OTA service bootloader

2.2.1

Reset Manager

The Flash base for STM32L1 starts at 0x8000000, meaning that at device reset, the

microcontroller will start executing application images sitting on that boundary. All the

BlueNRG and BlueNRG-MS kits platforms are preprogrammed with a DFU application

allowing the download of binary images into the internal Flash of the STM32L. Once the

OTA bootloader writes a new image starting from a base address that is above the Flash

base + DFU size (0x3000), we need a way to allow transfer of control towards the new

application every time we reset. For that purpose, every device on which we plan to include

the OTA bootloader service will, at first, need to be loaded with a Reset Manager starting

from the Flash base address + DFU size. At device reset, the Reset Manager will take care

of jumping to the location of the last image that was successfully loaded by the OTA

bootloader, as indicated in the higher 8 bytes within the EEPROM memory range of the

device (starting at address 0x08080FF8). To summarize, Figure 3: "BLE OTA service

bootloader Flash layout" shows a typical Flash memory layout for a device with OTA

bootloader service on-board, with an STM32L as the host microcontroller. At device initial

setup, we will utilize the BlueNRG GUI in order to upload in Flash the application into the

STM32L at address 0x8003800 (Reset Manager upper end), then we will do the same in

order to upload the Reset Manager itself at address 0x8003000. Actions must be taken to

erase the relevant EEPROM locations for proper Reset Manager initial setup as well. On

the BlueNRG and BlueNRG-MS kits platform, this can be achieved by keeping BUTTON_2

pressed while pushing the reset (LED_D1 will light up for five seconds). This will cause

EEPROM location erase, which means an “all 0” read by the Reset Manager after next

pushing of the reset button. As a consequence, by default the Reset Manager assumes

that it must jump to 0x8003800, which is exactly the reference base address for the

application to run at first setup.