Re: [Suit] SUIT architecture examples

[David Brown <[e-mail]>]

On Sat, Jun 23, 2018 at 10:23:09AM -0400, Michael Richardson wrote:
>
>David Brown <[e-mail]> wrote:
>    > ### Dual CPU, other bus
>
>    > This configuration has two or more CPUs, each having their own memory.
>    > There will be a communication channel between them, but it will be used
>    > as a peripheral, not via shared memory.  In this case, each CPU will
>    > have to be responsible for its own firmware upgrade.  It is likely that
>    > one of the CPUs will be considered a master, and will direct the other
>    > CPU to do the upgrade.  This configuration is commonly used to offload
>    > specific work to other CPUs.  Firmware dependencies are similar to the
>    > other solutions above, sometimes allowing only one image to be
>    > upgraded, other times requiring several to be upgraded atomically.
>    > Because the updates are happening on multiple CPUs, upgrading the two
>    > images atomically is challenging.
>
>Is there sometimes an ordering constrained between images?
>I.e. upgrade CPU-A to version X, before you upgrade CPU-B to version X?
>
>Does the Manifest need to specify this constraint, or would it be implied?

The current requirements as I am aware of them, only require the two
images either be updated independently, or both be updated atomically.
But, maybe it is worth being able to specify a one-directional
ordering.  In fact, a one-directional ordering could be used for the
atomic case by just having each image specify a dependency on the
other image at that version.

David