Single-image handling UM2262
70/94 UM2262 Rev 6
Appendix C Single-image handling
Some SBSFU application examples handle one single firmware image stored in internal
Flash.
This mode of operation allows maximizing the user firmware size by:
• Reducing the SBSFU footprint in Flash
• Allocating more Flash space for the user application
These benefits come at the cost of some features:
• Safe firmware image programming cannot be ensured: as soon as an installation is
interrupted (power off), the firmware update process must be restarted from the
beginning (including the download phase).
• The user application cannot download a new firmware image: the local download
procedure is the only way to update the active user code.
C.1 Elements and roles
Slot #0:
• This slot contains the active firmware (firmware header + firmware). This is the user
application that is launched at boot time by SBSFU (after verifying its validity).
• This slot is directly updated when a new firmware image is downloaded and installed
(after firmware header verification)
C.2 Mapping definition
The mapping definition is located in the Linker_Common folder for each example. Figure 38
shows how to find information such as slot size and SBSFU code size in the NUCLEO-
L432KC example.
To start the application, SBSFU initializes the SP register with the user application stack
pointer value, then jumps to the user application reset vector (refer to
Figure 38: User
application vector table (example of the STM32L4 Series)).
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