2.7 KiB
Flash partitions
Flash memory partitions
To integrate wolfBoot you need to partition the flash into separate areas (slots), according to the geometry of the flash memory.
Images boundaries must be aligned to physical sectors, because the bootloader erases all the flash sectors before storing a firmware image.
The flash memory of the target is partitioned into the following areas:
- Bootloader partition, at the beginning of the flash
- Primary slot (boot partition) starting at address
FLASH_AREA_IMAGE_0_OFFSET - Secondary slot (upgrade partition) starting at address
FLASH_AREA_IMAGE_1_OFFSET - Scratch space (swap partition) starting at address
FLASH_AREA_IMAGE_SCRATCH_OFFSET
A proper partitioning configuration must be set up for the specific use, by setting the values for offsets and sizes in include/target.h.
Bootloader partition
This partition is usually very small, and only contains the bootloader code and data. Public keys pre-authorized during factory image creations are automatically stored as part of the firmware image.
Primary slot (boot partition)
This is the only partition from where it is possible to chain-load and execute a
firmware image. The firmware image must be linked so that its entry-point is at address
FLASH_AREA_IMAGE_0_OFFSET + 256.
Secondary slot (upgrade partition)
The running firmware is responsible of transferring a new firmware image through a secure channel, and store it in the secondary slot. If an upgrade is initiated, the bootloader will replace or swap the firmware in the boot partition at the next reboot.
Example 512KB partitioning on STM32-F407
The example firmware provided in the test-app is configured to boot from the primary partition
starting at address 0x20000. The flash layout is provided by the default example using the following
configuration in target.h:
#define FLASH_AREA_IMAGE_0_OFFSET 0x20000
#define FLASH_AREA_IMAGE_0_SIZE 0x20000
#define FLASH_AREA_IMAGE_1_OFFSET 0x40000
#define FLASH_AREA_IMAGE_1_SIZE 0x20000
#define FLASH_AREA_IMAGE_SCRATCH_OFFSET 0x60000
#define FLASH_AREA_IMAGE_SCRATCH_SIZE 0x20000
which results in the following partition configuration:
This configuration demonstrates one of the possible layouts, with the slots aligned to the beginning of the physical sector on the flash.
The entry point for all the runnable firmware images on this target will be 0x20100,
256 Bytes after the beginning of the first flash partition. This is due to the presence
of the firmware image header at the beginning of the partition, as explained more in details
in Firmware image