Allow using separate page sizes for state and dfu

* Less generics on bootloader. Keep PAGE_SIZE as a common multiple of
DFU and ACTIVE page sizes.
* Document restriction
* Add unit tests for different page sizes

1 files changed, 2 insertions, 1 deletions

diff --git a/docs/modules/ROOT/pages/bootloader.adoc b/docs/modules/ROOT/pages/bootloader.adoc
index 1a984d6d..7539774c 100644
--- a/docs/modules/ROOT/pages/bootloader.adoc
+++ b/docs/modules/ROOT/pages/bootloader.adoc
@@ -27,6 +27,7 @@ The bootloader divides the storage into 4 main partitions, configured by a linke
 * DFU - Where the application-to-be-swapped is placed. This partition is written to by the application.
 * BOOTLOADER STATE - Where the bootloader stores the current state describing if the active and dfu partitions need to be swapped. When the new firmware has been written to the DFU partition, a flag is set to instruct the bootloader that the partitions should be swapped.
 
-The partitions for ACTIVE (+BOOTLOADER), DFU and BOOTLOADER_STATE may be placed in separate flash, but they have to support compatible page sizes.
+The partitions for ACTIVE (+BOOTLOADER), DFU and BOOTLOADER_STATE may be placed in separate flash. The page size used by the bootloader is determined by the lowest common multiple of the ACTIVE and DFU page sizes.
+The BOOTLOADER_STATE partition must be big enough to store one word per page in the ACTIVE and DFU partitions combined.
 
 The bootloader has a platform-agnostic part, which implements the power fail safe swapping algorithm given the boundaries set by the partitions. The platform-specific part is a minimal shim that provides additional functionality such as watchdogs or supporting the nRF52 softdevice.