Forum: System Workbench for STM32

Locate Heap in SDRAM

Posted by FranzWegerer on 2016-02-08 13:49

Hello,

I want to locate heap in SDRAM. I found some Keil samples, but ...

SDRAM adress is 0xD0000000, size 8M.

Thanks a lot

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Posted by tarek bouchkati on 2016-02-08 16:07 Tunisia

Hello Franz,

you need to specify SDRAM memory in your linker file (here I am using a linker for STM32L476RGTx with 1M FLASH and 96K RAM)

 
/* Specify the memory areas */
MEMORY
{
FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 1M
RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 96K
SDRAM(xrw)    : ORIGIN = 0x????????, LENGTH = 8M
}


And modify >RAM by >SDRAM 

xxxxxxxxxx
 
/* User_heap_stack section, used to check that there is enough RAM left */
  ._user_heap_stack :
  {
    . = ALIGN(4);
    PROVIDE ( end = . );
    PROVIDE ( _end = . );
    . = . + _Min_Heap_Size;
    . = . + _Min_Stack_Size;
    . = ALIGN(4);
  } >SDRAM


Update:
Do not forget to initialize you SDRAM before your application starts !
It should be done in Reset Handler (in startup file) in assembly.

There are better solutions that writing in assembler
1- Start with the default STACK&HEAP location (RAM), initialize your SDRAM then switch to SDRAM as STACK&HEAP location
2- Separate Heap and stack locations (STACK in RAM and HEAP in SDRAM) in linker file, than initialize SDRAM in your main before any malloc usage

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Posted by FranzWegerer on 2016-02-09 20:26

First - thank you very much!

Yes I want only heap into SDRAM (the heap can use the whole SDRAM), but how can I split this? Sorry, but I am not very familiar with linker scripts

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Posted by tarek bouchkati on 2016-02-10 13:37 Tunisia

We can also do that without big modifcations in linker script biggrin

by defining the heap start/end in linker miscellaneous flags, ie : 

xxxxxxxxxx
 
-Wl,--defsym=__heap_start=0xD0000000,--defsym=__heap_limit=0xD0800000

Note: you have to change these values with yours

and removing heap informations from linker (not necessary but good for your linker lisibility)

1- remove this line :
_Min_Heap_Size = 0; /* required amount of heap */
2- and replace this 

xxxxxxxxxx
 
/* 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

with the following 

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



Edit: I forgot syscalls modifications mrgreen

You have to add syscalls.c to project (you can borrow it from another SystemWorkbench project)
then replace _sbrk function by the following

​x
 
caddr_t _sbrk(int incr)
{
    extern char __heap_start asm("__heap_start"); /* Defined by the linker. */
    extern char __heap_limit asm("__heap_limit"); /* Defined by the linker. */
​
    static char *heap_end;
    static char *heap_limit = &__heap_limit;
​
    char *prev_heap_end;
​
    if (heap_end == 0)
        heap_end = &__heap_start;
​
    prev_heap_end = heap_end;
    if (heap_end + incr > heap_limit)
    {
        errno = ENOMEM; // not enough memory
        return (caddr_t) -1;
    }
​
    heap_end += incr;
​
    return (caddr_t) prev_heap_end;
}
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Posted by FranzWegerer on 2016-02-16 15:13

Thanks again. Works without any problems.
I think it is easier to define the symbols in linker script.

Attached the final code with all modifications

code.zip (3.83 Kb)
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Posted by Csongor on 2019-09-13 12:12

Hello guys!
I have a similar problem. I want to locate heap in SDRAM in Nucleo144
H743ZI hardware.
Your conversation and solution is very helpfully and interesting, but
i have a lot of question about this topic.

First question:
Can I have to change something in the CubeMX FMC Mode & Configuration
SDRAM 1? Because I don’t realize it is important to me. Nobody speaks
about it. When I was searching on the internet for my problem
solution, I only found about, how to change something in for example:
STM32H743ZITx_FLASH.ld file. You guys are the first solution, who
spoke about it, that I must to change something in the syscall.c file.

Second question:
What is the easiest way to test my SDRAM is working? Nowadays I use malloc function to see this.
Is it correct or do you have any better idea?

Thanks a lot!
Csongor

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