# STM32F407VET6 “RAM overflow” while using only 2/3 of it (as far as I know)

I need to declare ~153 KB buffer as a framebuffer for display (more precisely at least two buffers, as one must be in CCMRAM to have enough space) and as this MCU has 192 KB RAM in total, it clearly should be possible. But as soon as I declare buffer in CCMRAM (framebuffer2) to be of size 65536 and buffer in normal RAM more than 63798 (framebuffer1), linker gives me "RAM overflowed by ..." error.

I'm pretty new to this, so I don't know exactly why is this happening, whether it is wrong linker definition, or some debug features taking up space, or something else. I'm working with CubeMX generated HAL project in SystemWorkbench with Ac6 compiler.

/*
*****************************************************************************
**

**
**  Abstract    : Linker script for STM32F407VETx Device with
**                512KByte FLASH, 128KByte RAM
**
**                Set heap size, stack size and stack location according
**                to application requirements.
**
**                Set memory bank area and size if external memory is used.
**
**  Target      : STMicroelectronics STM32
**
**
**  Distribution: The file is distributed as is, without any warranty
**                of any kind.
**
*****************************************************************************
** @attention
**
**
** Redistribution and use in source and binary forms, with or without modification,
** are permitted provided that the following conditions are met:
**   1. Redistributions of source code must retain the above copyright notice,
**      this list of conditions and the following disclaimer.
**   2. Redistributions in binary form must reproduce the above copyright notice,
**      this list of conditions and the following disclaimer in the documentation
**      and/or other materials provided with the distribution.
**   3. Neither the name of Ac6 nor the names of its contributors
**      may be used to endorse or promote products derived from this software
**      without specific prior written permission.
**
** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
** AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
** IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
** DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
** FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
** DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
** SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
** OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
**
*****************************************************************************
*/

/* Entry Point */
ENTRY(Reset_Handler)

/* Highest address of the user mode stack */
_estack = 0x20020000;    /* end of RAM */
/* Generate a link error if heap and stack don't fit into RAM */
_Min_Heap_Size = 0x200;      /* required amount of heap  */
_Min_Stack_Size = 0x400; /* required amount of stack */

/* Specify the memory areas */
MEMORY
{
RAM (xrw)      : ORIGIN = 0x20000000, LENGTH = 128K
CCMRAM (rw)      : ORIGIN = 0x10000000, LENGTH = 64K
FLASH (rx)      : ORIGIN = 0x8000000, LENGTH = 512K
}

/* Define output sections */
SECTIONS
{
/* The startup code goes first into FLASH */
.isr_vector :
{
. = ALIGN(4);
KEEP(*(.isr_vector)) /* Startup code */
. = ALIGN(4);
} >FLASH

/* The program code and other data goes into FLASH */
.text :
{
. = ALIGN(4);
*(.text)           /* .text sections (code) */
*(.text*)          /* .text* sections (code) */
*(.glue_7)         /* glue arm to thumb code */
*(.glue_7t)        /* glue thumb to arm code */
*(.eh_frame)

KEEP (*(.init))
KEEP (*(.fini))

. = ALIGN(4);
_etext = .;        /* define a global symbols at end of code */
} >FLASH

/* Constant data goes into FLASH */
.rodata :
{
. = ALIGN(4);
*(.rodata)         /* .rodata sections (constants, strings, etc.) */
*(.rodata*)        /* .rodata* sections (constants, strings, etc.) */
. = ALIGN(4);
} >FLASH

.ARM.extab   : { *(.ARM.extab* .gnu.linkonce.armextab.*) } >FLASH
.ARM : {
__exidx_start = .;
*(.ARM.exidx*)
__exidx_end = .;
} >FLASH

.preinit_array     :
{
PROVIDE_HIDDEN (__preinit_array_start = .);
KEEP (*(.preinit_array*))
PROVIDE_HIDDEN (__preinit_array_end = .);
} >FLASH
.init_array :
{
PROVIDE_HIDDEN (__init_array_start = .);
KEEP (*(SORT(.init_array.*)))
KEEP (*(.init_array*))
PROVIDE_HIDDEN (__init_array_end = .);
} >FLASH
.fini_array :
{
PROVIDE_HIDDEN (__fini_array_start = .);
KEEP (*(SORT(.fini_array.*)))
KEEP (*(.fini_array*))
PROVIDE_HIDDEN (__fini_array_end = .);
} >FLASH

/* used by the startup to initialize data */

/* Initialized data sections goes into RAM, load LMA copy after code */
.data :
{
. = ALIGN(4);
_sdata = .;        /* create a global symbol at data start */
*(.data)           /* .data sections */
*(.data*)          /* .data* sections */

. = ALIGN(4);
_edata = .;        /* define a global symbol at data end */
} >RAM AT> FLASH

/* CCM-RAM section
*
* IMPORTANT NOTE!
* If initialized variables will be placed in this section,
* the startup code needs to be modified to copy the init-values.
*/
.ccmram :
{
. = ALIGN(4);
_sccmram = .;       /* create a global symbol at ccmram start */
*(.ccmram)
*(.ccmram*)

. = ALIGN(4);
_eccmram = .;       /* create a global symbol at ccmram end */
} >CCMRAM AT> FLASH

/* Uninitialized data section */
. = ALIGN(4);
.bss :
{
/* This is used by the startup in order to initialize the .bss secion */
_sbss = .;         /* define a global symbol at bss start */
__bss_start__ = _sbss;
*(.bss)
*(.bss*)
*(COMMON)

. = ALIGN(4);
_ebss = .;         /* define a global symbol at bss end */
__bss_end__ = _ebss;
} >RAM

/* User_heap_stack section, used to check that there is enough RAM left */
._user_heap_stack :
{
. = ALIGN(8);
PROVIDE ( end = . );
PROVIDE ( _end = . );
. = . + _Min_Heap_Size;
. = . + _Min_Stack_Size;
. = ALIGN(8);
} >RAM

/* Remove information from the standard libraries */
{
libc.a ( * )
libm.a ( * )
libgcc.a ( * )
}

.ARM.attributes 0 : { *(.ARM.attributes) }
}

• The program needs RAM space as well... – Peter Smith Mar 19 '17 at 14:05
• That exactly is the question I'm trying to find answer to – what part of program which I don't know about takes up 40 kB of space in RAM, when almost nothing else is running. I regularly run STM32F0 with 20 kB total RAM, so I doubt that HAL is that power hungry. I cannot find anything in output.map which would take up this amount of memory. – wildfireheart Mar 19 '17 at 17:35
• The memory map may currently require more application RAM than is apparent from the linker script. Once I get to my development system tomorrow I will check. – Peter Smith Mar 19 '17 at 17:56
• Look at the .map file produced by the linker to understand how much memory is being used and how much is available. – kkrambo Mar 19 '17 at 19:18
• @PeterSmith Ok, thank you very much. I'll try to make minimum test case tomorrow. Now I have literally almost empty CubeMX HAL project with 2 SPIs, DAC and WWDG enabled. – wildfireheart Mar 19 '17 at 20:26

After investigating output.map I found, that the problem was simple typo. I had buffer declared as

uint8_t buffer2[64000] __attribute__((section("ccmram")));


which I blindly copied from OpenSTM32.org site and was probably for some different version of HAL. As the correct identifier of core coupled memory in my .ld script is .ccmram, not ccmram, linker was putting the buffer into normal RAM, therefore "RAM overflow". Correct definition is:

uint8_t buffer2[64000] __attribute__((section(".ccmram")));


with which buffer is placed into correct memory:

 *(.ccmram)
.ccmram        0x0000000010000000     0xfa00 Src/main.o
0x0000000010000000                buffer2
*(.ccmram*)


Sorry for mistake, I'll leave this here in case it helps anyone (or future me).