docs: Update Image Trailer documentation according to latest changes (41f123c2) · Commits · Wenxi XU / Mcuboot

docs/design.md

+54 −9

Original line number	Diff line number	Diff line
		@@ -452,16 +452,28 @@ image trailer. An image trailer has the following structure:
		\| Encryption key 0 (16 octets) [*] \|
		\| \|
		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
		\| 0xff padding as needed \|
		\| (BOOT_MAX_ALIGN minus 16 octets from Encryption key 0) [*] \|
		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
		\| Encryption key 1 (16 octets) [*] \|
		\| \|
		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
		\| 0xff padding as needed \|
		\| (BOOT_MAX_ALIGN minus 16 octets from Encryption key 1) [*] \|
		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
		\| Swap size (4 octets) \|
		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
		\| Swap info \| 0xff padding (7 octets) \|
		\| 0xff padding as needed \|
		\| (BOOT_MAX_ALIGN minus 4 octets from Swap size) \|
		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
		\| Swap info \| 0xff padding (BOOT_MAX_ALIGN minus 1 octet) \|
		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
		\| Copy done \| 0xff padding (BOOT_MAX_ALIGN minus 1 octet) \|
		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
		\| Copy done \| 0xff padding (7 octets) \|
		\| Image OK \| 0xff padding (BOOT_MAX_ALIGN minus 1 octet) \|
		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
		\| Image OK \| 0xff padding (7 octets) \|
		\| 0xff padding as needed \|
		\| (BOOT_MAX_ALIGN minus 16 octets from MAGIC) \|
		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
		\| MAGIC (16 octets) \|
		\| \|
		@@ -540,16 +552,49 @@ of 3 is explained below.
		6. Image OK: A single byte indicating whether the image in this slot has been
		confirmed as good by the user (0x01=confirmed; 0xff=not confirmed).

		7. MAGIC: The following 16 bytes, written in host-byte-order:
		7. MAGIC: A 16-byte field identifying the image trailer layout. It may assume
		distinct values depending on the maximum supported write alignment
		(`BOOT_MAX_ALIGN`) of the image, as defined by the following construct:

		``` c
		const uint32_t boot_img_magic[4] = {
		0xf395c277,
		0x7fefd260,
		0x0f505235,
		0x8079b62c,
		union boot_img_magic_t
		{
		struct {
		uint16_t align;
		uint8_t magic[14];
		};
		uint8_t val[16];
		};
		```
		If `BOOT_MAX_ALIGN` is 8 bytes, then MAGIC contains the following 16 bytes:

		``` c
		const union boot_img_magic_t boot_img_magic = {
		.val = {
		0x77, 0xc2, 0x95, 0xf3,
		0x60, 0xd2, 0xef, 0x7f,
		0x35, 0x52, 0x50, 0x0f,
		0x2c, 0xb6, 0x79, 0x80
		}
		};
		```

		In case `BOOT_MAX_ALIGN` is defined to any value different than 8, then the maximum
		supported write alignment value is encoded in the MAGIC field, followed by a fixed
		14-byte pattern:

		``` c
		const union boot_img_magic_t boot_img_magic = {
		.align = BOOT_MAX_ALIGN,
		.magic = {
		0x2d, 0xe1,
		0x5d, 0x29, 0x41, 0x0b,
		0x8d, 0x77, 0x67, 0x9c,
		0x11, 0x0f, 0x1f, 0x8a
		}
		};
		```

		---
		*Note*
		Be aware that the image trailers make the ending area of the image slot

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