I'm new to Zephyr and have inherited a project that uses the stm32 h747 disco board. The last build shows:
Memory region Used Size Region Size %age Used
FLASH: 363268 B 1 MB 34.64%
RAM: 441160 B 512 KB 84.14%
EXTMEM: 0 GB 256 MB 0.00%
SRAM1: 0 GB 128 KB 0.00%
SRAM2: 0 GB 128 KB 0.00%
SRAM3: 16 KB 32 KB 50.00%
SRAM4: 48 KB 64 KB 75.00%
SDRAM2: 3000 KB 32 MB 9.16%
IDT_LIST: 0 GB 32 KB 0.00%
Since RAM is approaching its limit, I would like to move the data in some specific source files to SRAM1 or SRAM2.
So, I modified the source code to move some large buffers to SRAM1 by using the __attribute__ to assign the buffers to SRAM1. After which, the build result is:
Memory region Used Size Region Size %age Used
FLASH: 363268 B 1 MB 34.64%
RAM: 441160 B 512 KB 84.14%
EXTMEM: 0 GB 256 MB 0.00%
SRAM1: 128KB 128 KB 100.00%
SRAM2: 0 GB 128 KB 0.00%
SRAM3: 16 KB 32 KB 50.00%
SRAM4: 48 KB 64 KB 75.00%
SDRAM2: 3000 KB 32 MB 9.16%
IDT_LIST: 0 GB 32 KB 0.00%
I was very surprised to see that although the buffers now occupy 100% of SRAM1, the RAM usage did not decrease from the prior 84%. I did an objdump and it appears that the buffers are also in the bss section, which is I think perhaps why the 84% did not decrease.
However, I do not know how to tell the compiler/linker that the buffers do not need to be initialized.
I suspect that I need to modify the linker command to do this, but it appears that the west build process auto-generates the linker script command. I don't know which file(s) I need to modify to remove the buffers from bss section. Is the auto-generated linker script dependent on the source code?
I *think* that what I need is for the resulting linker.cmd file to add a new section like
xy_stm32 (NOLOAD) : ALIGN_WITH_INPUT
{
. = ABSOLUTE(sram1-starting-address);
*(.variable_x) . = ABSOLUTE(starting-address) + size-of-x;
*(.variable_y) . = ABSOLUTE(starting-addresss) + size-of-y;
} > "SRAM1" AT > "SRAM1"
Is this correct?
How do I make the auto-gen liinker.cmd file add this? (if correct) And is this how to preclude the buffers from being in the bss section?
