stm32f429I-DISC1: mbed use sdram as heap

[krid]

Hello,

target: stm32f429I-DISC1

How can I use the SDRAM as heap?

First I initialized the SDRAM stting GPIOs, fmc, clock… -> SDRAM accessable, fine.
Next I modified the linker script and enabled a SDRAM memory section and moved the heap into SDRAM

SDRAM (rwx) : ORIGIN = 0xD0000000, LENGTH = 8M
    .heap (NOLOAD):
    {
        __uvisor_heap_start = .;
        __end__ = .;
        end = __end__;
        . += HEAP_SIZE;
        __HeapLimit = .;
        __uvisor_heap_end = .;
    } > SDRAM
On project build I get the ASSERT-error "Region RAM overflowed with stack and heap".

I commented that out. No need for testing.

If I now allocate memory by using “new” I get until _sbrk in mbed_retarget.cpp which fetches a valid pointer from SDRAM:

    static unsigned char* heap = (unsigned char*)&__end__;
    unsigned char*        prev_heap = heap;
    unsigned char*        new_heap = heap + incr;

but compares it to the MSP

if (new_heap >= (unsigned char*)__get_MSP()) {

and then gives ENOMEM

errno = ENOMEM;
 return (caddr_t)-1;
 }

because new_heap (0xD0nnnnnn) is greater than MSP (0x200mmmmm).

 

Do I really have to implement my own _sbrk syscall in order to put the HEAP onto the SDRAM?

 

Thanks

best regards

dirk

• This topic was modified 7 years, 5 months ago by krid.

[support]

Hi,

You could try using the _sbrk() implementation that comes from our “Fixed-size stack and heap” framework described in this tutorial: https://visualgdb.com/tutorials/arm/stack/

You would need to modify the linker script to place the “.heap” section into SDRAM and explicitly set the heap size via VisualGDB Project Properties.

[Author]

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