ChibiOS Free Embedded RTOS

Hi Forum,

I have a strange issue. I am using STM32F767ZIT6 micro controller for my project. Since I ran out of space in ram3 , I tried to use `ram0` using the . `DATA_RAM` alias is defined in `ARMCMx/compilers/GCC/ld/STM32F76xxI.ld` .

I then declared a "global" struct as follows

As per the C standard, all members in the struct should be initialised to zero using the syntax, right? However, I see that a few members are not initialized to zero. When I remove `__attribute__((section("DATA_RAM")))` the members are initialized to zero. Has anyone faced a similar issue, if so did you manage to solve it ?

I did some debugging and noticed the following.
I printed memory usage using

--print-memory-usage

in os/common/startup/ARMCMx/compilers/GCC/mk/rules.mk by editing the following line



This would however print ram0 as full. This is not true since I have rarely used DATA_RAM (ram0). Does this mean that the linker script is what that's causing the trouble ? The linker could also be wrong since ram1 and ram2 are marked as 0.00% being used, ram0 is the sum of ram1 and ram2.


Thanks and Regards,

Akshai M

Akshai,

ChibiOS only zeroes the ".bss*" and ".ramX_clear*" sections on startup. Try putting the array in the ".ram0_clear" section. See rules_memory.ld next to your linker script, and crt1.c a few levels up for how that works.

Ram0 is full due to the rest of the free memory being stolen for the heap (last rule in rules_memory.ld). I recall changing CH_CFG_MEMCORE_SIZE allowed you to see the true used size, but it isn't doing that for me right now (optimization / discard fail?).

The ram0 vs ram1+ram2 thing is due to the linker printing the size of things it put exactly in that section. It doesn't double count the used size for overlapping regions.

Patrick

Hi,

Psyco is correct, all the RAM not used by the application is allocated to the default heap, allocators use that area:

- Core allocator.
- Heap allocator.
- C runtime allocator (malloc, free).

Also the suggestion about the clear regions is on spot.

Giovanni

Thanks, Patrick and Giovanni.

Change from `DATA_RAM` to `.ram0_clear` did the trick

Also, I tried changing the `CH_CFG_MEMCORE_SIZE`, but still, as Patrick already pointed out the `ramo` utilization stays at 100%. Any suggestion on how to make it print the right amount being used?

Regards,

Akshai M

Hi,

The best way is to look into the .map file, all real values are in there.

Giovanni

Thanks, Giovanni . I shall do that.

Also, do you think it's okay to set up the LD Script to zero sections in `ram0` as well? Does it add any overhead? I expect the startup timing could be stretched a bit. Any particular reason why you did not zero it?

Regards,

Akshai M

Hi,

You may want RAM portions to not be cleared at startup (startup time, storing cross-reset data), this is why in only clears/inits specific parts.

Giovanni