Based on what you've written in this post as well as the reply to Kerm's post on Cemetech, it seems like you're losing quite a bit of the flexibility that Qwerty.55's format was going to have. You have identifiers for which shell the program is for, and even what version of the SDK it was made with... These don't really have a purpose, unless you plan to treat programs that are for different shells/made with different versions of the SDK in separate ways. This is bad, because then old versions of shells won't be able to read those new files!
On the 8x calcs, programs from old shells work in new shells, but not vice-versa. Sometimes someone might want to use an older shell because they like it better, but they won't be able to do that. If we design this format in a good way, we might be able to avoid that problem completely on the Prizm. Programs should be made for all Prizm shells - not a specific shell on the Prizm. The format that Qwerty.55 suggested allowed new shells to add new features in files by adding new packages, while still allowing the files to work correctly with older shells, unless the packet was "critical", as indicated by a list.
There are also a few things with the packets that you currently have that I would like to be changed. (It's a good idea to split your packets a bit so that you don't have everything in one packet!)
1. Unlike Qwerty.55's format, the size of the packets don't seem to be stored anywhere. How is the shell supposed to know where they end in cases where the size of the packet isn't obvious?
2. Like I said before, I don't see the point in storing the SDK version and the program's shell.
3. The description of the program shouldn't be in the critical packet, because it's not necessary to include a description for every program.
4. The checksum should also be optional. Don't place it in the critical packet.
5. It's better to indicate main() by giving it a packet ID. "file offset to main" shouldn't be necessary.
6. Does "size of main" have a purpose?
7. Why do we need to include the first four characters of the author's name?
8. Please don't require programmers to include an author icon if they don't include an author name. The icon should be a separate packet.
9. Why is the author's name stored twice, once before the icon and once after?
Okay I'll try to answer these questions as best as I can
1. Thinking about it now, to allow for newer programs to run on older shells the size of a packet should be the second word included that way Walnut can skip past unfamiliar packets. Otherwise Walnut was going to rely on knowing the size of the packet based off the SDK version but that can now be fixed.
2. The SDK version number allows for Walnut to know which version of the packet layout is being used. Having an SDK version number higher than the shell number shouldn't prevent a program from running but may cause some errors in displaying data. The way each packet is arranged shouldn't change once Walnut is released so that is why I want to get all the issues out now by making this public. Also for the "wnut" that is just an identifier that the shell uses so it knows that the file was designed for Walnut and uses the Walnut packet layout. It is just like how java .class files start with 0xcafebabe as an identifier.
3. That can be moved easily to another packet but even if the developer doesn't want to include a description that field will only take 1 byte if blank. The description is like a subtext that can be displayed with the title.
4. The reason for the checksum being there was that if there was a binary error in the header or executable then there is a possibility that the calculator could crash or even brick. For example if the FRQCR field was corrupted
Don't forget that the SDK will calculate that on it's own when a project is built similar to what mkg3a already does.
5. A packet for main is also doable. The reason for having the offset was so that it could be quickly located and wouldn't have to be searched for.
6. Size of main just means the size of the executable. This is very important as it affects what Walnut will write to the MMU when the program begins.
7. The first 4 letters could also be more like their initials. This data will never be displayed to the user but is so that Walnut has the ability to organize programs by author if the user wishes to do so.
8. They don't have to include an icon. By setting the icon compression mode to 0 it means that there is no image and Walnut will not expect one.