Hello,
I am working on STM32L431VC. I am using FreeRTOS and RTT technology to read logs from code. In FreeRTOS there is special #define (configTOTAL_HEAP_SIZE) to determine how much RAM FreeRTOS will use.
Recently I had to change this value from 20kB to 30kB. I noticed that RTT (and with it SystemView) stopped working. The clear root cause could be that I run out of RAM on my system.
But this is not a case, my STM32L431VC has 64kB of RAM, and with configTOTAL_HEAP_SIZE = 30 kB I can still allocate (with malloc) 20 kB in main() so probably 20kB is more then enough for RTT.

I found similar problem on nordic semi webpage devzone.nordicsemi.com/f/nordi…sing-more-than-8kb-of-ram but increasing the BUFFER_SIZE_UP to 2048 (which helped) do not work for me.


has anyone encountered such a problem? I will be very grateful for any help.



Best,

Marcin

Hello Nino,
sorry for the delay. It actually should be easy to reproduce. To test it on empty project I just generated new project with STM32CubeMX (+FreeRTOS),
then I added RTT files. On my test board:
when
#define configTOTAL_HEAP_SIZE ((size_t)10000) RTT working
and when
#define configTOTAL_HEAP_SIZE ((size_t)40000) RTT not working


I am adding my whole project to this reply.

Thanks for any help/ideas.


Marcin

Just to add to my previous comment:
I made today really a lot of tests and I found out something very strange. I was looking for different dependencies (I mean I was wondering why changing configTOTAL_HEAP_SIZE influence RTT).

And it turns out that making configTOTAL_HEAP_SIZE bigger is pushing

.bss._acDownBuffer
.bss._acUpBuffer
down in my RAM memory. I do not know why but somewhere around values:

.bss._acDownBuffer
0x20006fec 0x800 Src\SEGGER_RTT.o
.bss._acUpBuffer
0x200077ec 0x800 Src\SEGGER_RTT.o

RTT stops working. I took this idea and I moved RTT to the beginning of RAM (with #define SEGGER_RTT_SECTION ".rtt" and putting .rtt section in linker file)
And after this change it is working (I can make configTOTAL_HEAP_SIZE as big as I want again).


Maybe it will be some help to figure out what is going on.


Marcin

Ok, so I know what happened. RTT Viewer did not managed to find RTT Control block.
So if you have similar problems like I do you have 2 solutions:

1. Move RTT buffers to beginning of RAM with help of linker file
2. Check your map file and look for _SEGGER_RTT memory address. Then in RTT viewer set not "Auto Detection" in RTT Control Block but "Address" and put memory address you found in map file.


All the best,
Marcin