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docs/design: add notes about swap algorithms #2412

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6 changes: 6 additions & 0 deletions docs/design.md
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Expand Up @@ -183,6 +183,9 @@ one of these two strategies.

### [Swap using scratch](#image-swap-using-scratch)

Please note that the swap-using-scratch algorithm may be removed in the coming
future.

When swap-using-scratch algorithm is used, in addition to the slots of
image areas, the bootloader requires a scratch area to allow for reliable
image swapping. The scratch area must have a size
Expand Down Expand Up @@ -280,6 +283,9 @@ The algorithm is enabled using the `MCUBOOT_SWAP_USING_OFFSET` option.

### [Swap using move (without using scratch)](#image-swap-no-scratch)

Please note that the swap-using-offset algorithm is preferred over swap-using-move
except when building for existing products already using the latter.

This algorithm is an alternative to the swap-using-scratch algorithm.
It uses an additional sector in the primary slot to make swap possible.
The algorithm works as follows:
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