Markus:
I presume you are referring to these definitions:
#define sec_data_core __attribute__((section(".data.core")))
#define sec_bss_core __attribute__((section(".bss.core")))
#define sec_bss_nz_core __attribute__((section(".bss.core.nz")))
As far as I know there is no real magic here but I am sure there is some degree
of inconsistency.
The reason sec_bss_nz_core was added was to get around a HW problem with early
nordic chips (you can see the reference in nrf52.ld) so I do not doubt that
this is no longer used. Personally, I think the idea of having a “non-zeroed
.bss” is pretty cool. I guess one could simply call that the heap but sometimes
you just like allocating a global variable and not allocating it from the heap.
I realize that the only real reason to do this is save time in the startup code
zeroing out memory (but still; that is cool!) :-) Not quite sure why “core” was
added to that defintion. Maybe because there was some conflict with naming it
bss.nz?
I should probably look at the STM startup code to be sure of this but I presume
they use sec_data_core for both code and data they want to locate in CCM. This
is basically a .data section in that the startup code needs to copy this from
flash (whether it be code or initialized data).
I guess sec_bss_core is used to store variables in CCM that just need to get
zeroed by the startup code.
btw, I am no STM CPU/memory architecture expert but I was reading up on it and
they do not suggest putting both code and data into CCM. Of course, if you need
the RAM you need the RAM… Is that why you want to move a stack there? I guess
if all your code is executing from flash then putting data into CCM is fine
(maybe faster is SRAM is slower?).
Seems to me it would be nice to differentiate “core text” from “core data”. No
real reason I guess but seems a bit more intuitive. Might be nice to come up
with a set of “standard” section definitions (if they do not already exist
somewhere) that we can apply across all BSPs/MCUs.
> On Mar 31, 2018, at 4:02 PM, markus <[email protected]> wrote:
>
> I looked into moving the stack into the CCM memory of the stm32
> mcu's - and although almost every linker script defines ".data.core"
> sections and there are some defines in bsp.h's for section
> attributes they don't seem to be used.
>
> Is there some hidden magic going on or is the CCM reserved for
> application code?
>
> Have fun,
> Markus
