Specify linker section for CB and buffers

[NickeZ]

Hi,

To be able to "hand over" RTT from a bootloader to an app, I would like to specify the linker sections, so that I can place them on the same addresses in RAM. One can do that with SEGGER_RTT_SECTION and SEGGER_RTT_BUFFER_SECTION in the reference implementation.

I tested it out here NickeZ@c5e92bd and it works fine.

I use it with this addition to my linker file (before any other RAM entries):

    .rtt (NOLOAD) :
    {
        . = ALIGN(4);
        _srtt = .;
        *(.segger_rtt);
        *(.segger_rtt_buffer);
        _ertt = .;
    } > ram

Perhaps we could read those values from the environment, so that the app can specify them in the [env] section in .cargo/config.toml?

What do you think?

[NickeZ]

I tried to pass it in as an env variable / cfg. But "attribute values must be literals" means that something like #[cfg_attr(section_cb, link_section = section_cb)] is not possible to write.

I guess another option is to have optional parameters to the init_rtt macro?

I don't have much experience with macros, but something like this?

macro_rules! rtt_init {
    {
        $(up: { $($up:tt)* } )?
        $(down: { $($down:tt)* } )?
        $(section_cb: $section_cb:lit )?
        $(section_buf: $section_buf:lit )?
    } => { ... };
}