doc/reference: Added clarification on flash offset relation
Added information about that offsets are expressed in relation to
the flash memory beginning address.
This info was missing which cause misunderstanding of the concept
while contributing.
Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>
diff --git a/doc/reference/peripherals/flash.rst b/doc/reference/peripherals/flash.rst
index 0b8bf1e..e371a6c 100644
--- a/doc/reference/peripherals/flash.rst
+++ b/doc/reference/peripherals/flash.rst
@@ -6,6 +6,17 @@
Overview
********
+**Flash offset concept**
+
+Offsets used by the user API are expressed in relation to
+the flash memory beginning address. This rule shall be applied to
+all flash controller regular memory that layout is accessible via
+API for retrieving the layout of pages (see option:`CONFIG_FLASH_PAGE_LAYOUT`).
+
+An exception from the rule may be applied to a vendor-specific flash
+dedicated-purpose region (such a region obviously can't be covered under
+API for retrieving the layout of pages).
+
API Reference
*************
diff --git a/doc/reference/storage/flash_map/flash_map.rst b/doc/reference/storage/flash_map/flash_map.rst
index 788451d..2dab4f6 100644
--- a/doc/reference/storage/flash_map/flash_map.rst
+++ b/doc/reference/storage/flash_map/flash_map.rst
@@ -47,6 +47,9 @@
:language: DTS
:start-after: start-after-here
+Rule for offsets is that each partition offset shall be expressed in relation to
+the flash memory beginning address to which the partition belong.
+
The ``boot_partition``, ``slot0_partition``, ``slot1_partition``, and
``scratch_partition`` nodes are defined for MCUboot, though not all MCUboot
configurations require all of them to be defined. See the `MCUboot
