banking without bank switching with SILabs f12x

The compile error doesn't locate a function. It makes sure that you don't mistakenly create a call from bank1 <-> bank2, which won't work without the full bank switching implementation.

make sure that all that refer to "classic" is on bank 2 and all that refer to "modern is in bank 1"

If there are two headers, FormatClassic.h and FormatModern.h, then you make sure that all .c files that belong in bank 1 (modern) do not #include FormatClassic.h. (More generally, you could have two directories full of .h files.) You can enforce the restriction with the include path (and maybe a grep in the build process).

Actually getting the .c's into the right bank is fairly straightforward. If you wind up using the bank switch mechanism, there's a dropdown in uVision (or the linker directives). If you build two projects, then you just need the linker directive to put all the .c's in a group into high memory. Again, I'd probably keep the .c's in separate directories (common, classic, modern) to make it easy to generate a list of module names for each bank.

If you pick your module names carefully, you can use the wildcard feature of the linker directives to avoid having to manually maintain the list. You might write something like

(separately built)
SEGMENTS (?PR?Fmt*(0x8000))
or
(banked)
SEGMENTS (?PR?FmtCls*(B2:), ?PR?FmtMod(B1:))

if all the names happen to match one pattern.

A fancy build tool like Jam would let you create a custom function that takes a list of files and automatically wraps then in the proper linker directive. This is essentially doing the same job outside of the linker itself, and in the build tool instead.

The compile error doesn't locate a function. It makes sure that you don't mistakenly create a call from bank1 <-> bank2, which won't work without the full bank switching implementation.

make sure that all that refer to "classic" is on bank 2 and all that refer to "modern is in bank 1"

If there are two headers, FormatClassic.h and FormatModern.h, then you make sure that all .c files that belong in bank 1 (modern) do not #include FormatClassic.h. (More generally, you could have two directories full of .h files.) You can enforce the restriction with the include path (and maybe a grep in the build process).

Actually getting the .c's into the right bank is fairly straightforward. If you wind up using the bank switch mechanism, there's a dropdown in uVision (or the linker directives). If you build two projects, then you just need the linker directive to put all the .c's in a group into high memory. Again, I'd probably keep the .c's in separate directories (common, classic, modern) to make it easy to generate a list of module names for each bank.

If you pick your module names carefully, you can use the wildcard feature of the linker directives to avoid having to manually maintain the list. You might write something like

(separately built)
SEGMENTS (?PR?Fmt*(0x8000))
or
(banked)
SEGMENTS (?PR?FmtCls*(B2:), ?PR?FmtMod(B1:))

if all the names happen to match one pattern.

A fancy build tool like Jam would let you create a custom function that takes a list of files and automatically wraps then in the proper linker directive. This is essentially doing the same job outside of the linker itself, and in the build tool instead.