RFC tagged payload

[steven james]

Greetings,


I've been working with a tagging system so that multiple payloads in
firmware can be selected from serial at boot time.

The scheme adds a 16 byte tag block in front of each payload containing a
$TAG$ signature, additional block count, a payload length (optional, may
be 0), and a name string.

The idea is to search for tags in the ROM, present the name strings in a
list and allow selection of a particular target. The stream is then
positioned just past the tag and passed to elfboot.

changes:
elfboot no longer calls stream->init(), it presumes that has been done
already.

add stream methods:
searchtags
gettags
loadtag

search tags performs the search and specifies the neded buffer size to
hold the result.

gettags loads the tags into a provided buffer for presentation

loadtag positions the stream just after the selected tag index (0 based)

for backwards compatability:
Where no tags are found, the stream is positioned at the beginning

where the stream->searchtags == NULL, presume the stream object doesn't
support tags. Just call init and pass it to elfboot.

Yes, No, Comments?

G'day,
sjames


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