doc: design: clear up definition of an image trailer
The design document says that image trailers can be located in scratch. That's not true: the contents in scratch are just a subset of the complete image trailer. Fix this up by making it clear that image trailers are at the end of image areas, and sometimes some of their data is copied into and out of scratch. Signed-off-by: Marti Bolivar <marti.bolivar@linaro.org>
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@ -217,10 +217,12 @@ can be in:
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*** IMAGE TRAILER
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For the bootloader to be able to determine the current state and what actions
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should be taken during the current boot operation, it uses metadata existing
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on both slots, and while doing a swap operation it can be located in scratch.
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This metadata is located at the end of the slot and is called image trailer.
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An image trailer has the following structure:
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should be taken during the current boot operation, it uses metadata stored in
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the image flash areas. While swapping, some of this metadata is temporarily
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copied into and out of the scratch area.
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This metadata is located at the end of the image flash areas, and is called an
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image trailer. An image trailer has the following structure:
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0 1 2 3
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
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@ -236,8 +238,8 @@ An image trailer has the following structure:
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| MAGIC (16 octets) |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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These records are at the end of each image slot. The offset immediately
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following such a record represents the start of the next flash area.
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The offset immediately following such a record represents the start of the next
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flash area.
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Note: "min-write-size" is a property of the flash hardware. If the hardware
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allows individual bytes to be written at arbitrary addresses, then
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