[ECOS] Re: Moving one module to RAM

[Bart Veer <bartv at redhat dot com>]

>>>>> "Tim" == Tim Michals <tim@cygnetinc.com> writes:

    Tim> Can some give me a hint on how to move only one module code
    Tim> section to a RAM section. What I'm trying to do is run most
    Tim> of the code from ROM, POST, etc, then I would like move just
    Tim> a module with about 10 functions into RAM. This way I can
    Tim> call functions from ROM and they will run in ram, but for the
    Tim> module only.

    Tim> I was looking to using the attribute label on the functions
    Tim> but is there a easier way?

The way I would do this is indeed to use attributes on the function
declaration, e.g.:

    extern void foobar (void) __attribute__ ((section ("bar")));

combined with some linker script information which places that section
in the appropriate memory region.

There are probably many other approaches. A brief glance at the linker
documentation mentions a FILENAME command which can be used to place
some sections from given files into the current output section. You
might be able to do some section renaming on the intermediate .o file
by using objcopy with appropriate runes. You might be able to use some
inline assembler in the C source code to change the current output
section.

If the source file is compiled with -ffunction-sections then this
could cause a certain amount of extra confusion, in that the compiler
will automatically put each function into different sections. You may
be able to use this to your advantage, or it may cause extra
confusion.

Note that although you may want to execute the code from RAM, it still
has to be present in the ROM. This requires more linker script magic,
I believe you need to look at the documentation for the AT command.
Also, the code will not magically get copied from ROM to RAM, it will
be necessary to do a little bit of extra work in the startup.

Bart Veer // eCos net maintainer