imgtool: Add support for write_size > 8

[arvinf]

Increase write_size paramter to 16 to support SoCs such as Atmel SAM4S or
SAMV70 with 128-bit default flash alignments.

Signed-off-by: Arvin Farahmand arvinf@ip-logix.com

[d3zd3z]

If we plan to support these large alignments in the bootloader code, we should also add the 16-byte alignment to the end of image.rs. For large-writes, we test 128 and 512, but it looks like 16 will be common. A quick test with 'master' shows that setting the write alignment to 16 fails most tests at this point.

[d3zd3z]

I'm ok with these changes, although '> 8' might be a little misleading, since this only supports a write size of 16 in addition to currently supported sizes.

[arvinf]

I'll edit the commit message.

[utzig]

I believe this is misleading, since it won't really add any support for 16-byte alignments, only make a user believe it does by having that option in imgtool. Before bootutil supports alignments larger than 8-byte there is no reason to actually have this option. Also this duplicates effort which was already done in #949. Maybe you should work on improving that PR?

[arvinf]

My understanding was that bootutil gets the alignment from the flash device and uses it as-is. I'll take a look at the PR you referenced.

[utzig]

My understanding was that bootutil gets the alignment from the flash device and uses it as-is. I'll take a look at the PR you referenced.

It gets the alignment from the flash driver, if it comes from HW or from a constant in the flash driver depends on the implementation of the flash backend in the OS port. The issue is that there is also a local constant called MAX_BOOT_ALIGN which sets the limit we allow, so no matter what imgtool might get in the command line, it won't just work out of the box. And btw imgtool also uses a similar constant afair.

[arvinf]

Thank you for the clarification.

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