Enable all RAM on STM32H7 #16753

saraverbeecke · 2025-02-14T10:12:25Z

saraverbeecke
Feb 14, 2025

How can I enable all available RAM on a STM32H743/STM32H753?

The default linker script in the repo is:

/*
    GNU linker script for STM32H743
*/

/* Specify the memory areas */
MEMORY
{
    FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 1536K   /* sectors (0-7) + (0-3) */
    FLASH_APP  (rx) : ORIGIN = 0x08020000, LENGTH = 1408K   /* sectors (1-7) + (0-3) */
    FLASH_FS (r)    : ORIGIN = 0x08180000, LENGTH = 512K    /* sectors         (4-7) */
    DTCM (xrw)      : ORIGIN = 0x20000000, LENGTH = 128K    /* Used for storage cache */
    RAM (xrw)       : ORIGIN = 0x24000000, LENGTH = 512K    /* AXI SRAM */
    RAM_D2 (xrw)    : ORIGIN = 0x30000000, LENGTH = 288K
}

/* produce a link error if there is not this amount of RAM for these sections */
_minimum_stack_size = 2K;
_minimum_heap_size = 16K;

/* Define the stack.  The stack is full descending so begins just above last byte
   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
_estack = ORIGIN(RAM) + LENGTH(RAM) - _estack_reserve;
_sstack = _estack - 16K; /* tunable */

/* RAM extents for the garbage collector */
_ram_start = ORIGIN(RAM);
_ram_end = ORIGIN(RAM) + LENGTH(RAM);
_heap_start = _ebss; /* heap starts just after statically allocated memory */
_heap_end = _sstack;

/* Location of filesystem RAM cache */
_micropy_hw_internal_flash_storage_ram_cache_start = ORIGIN(DTCM);
_micropy_hw_internal_flash_storage_ram_cache_end = ORIGIN(DTCM) + LENGTH(DTCM);

/* Location of filesystem flash storage */
_micropy_hw_internal_flash_storage_start = ORIGIN(FLASH_FS);
_micropy_hw_internal_flash_storage_end = ORIGIN(FLASH_FS) + LENGTH(FLASH_FS);

/* Define output sections */
SECTIONS
{
    .eth_buffers (NOLOAD) : {
        . = ABSOLUTE(0x30040000);
        *eth.o*(.bss.eth_dma)
    } >RAM_D2
}

Since i don't need ethernet, I want to get rid of the .eth_buffers section and use all the available RAM as application RAM in micropython. Is this possible? I already tried to delete the eth_buffer section and altered the _heap_end like so:

_heap_end = ORIGIN(RAM_D2) + LENGTH(RAM_D2);

but no luck. Tips?

projectgus · 2025-02-17T22:59:50Z

projectgus
Feb 17, 2025
Collaborator

I already tried to delete the eth_buffer section and altered the _heap_end like so:

_heap_end = ORIGIN(RAM_D2) + LENGTH(RAM_D2);

but no luck. Tips?

The RAM and RAM_D2 regions aren't contiguous (RAM ends at 0x24080000 and RAM_D2 doesn't start until 0x3000000). This is why setting the heap to span both regions doesn't work. (The stack is also placed after the heap in the main RAM region.)

We have support in MicroPython for discontinuous heap regions (look for MICROPY_GC_SPLIT_HEAP in the code), so you could possibly add both memory regions to the heap. However, this has not been used on stm32 before so you'll probably need to do some extra porting work before it's possible.

(Note also that, as far as I understand the STM32H7 architecture, the D2 region is going to be slower for the CPU to access compared to the main SRAM region.)

0 replies

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

MicroPython

Enable all RAM on STM32H7 #16753

Uh oh!

{{title}}

Uh oh!

Replies: 1 comment

Uh oh!

{{title}}

Uh oh!

Uh oh!

{{editor}}'s edit

{{editor}}'s edit

Uh oh!

Select a reply

Uh oh!

MicroPython

Enable all RAM on STM32H7 #16753

Uh oh!

saraverbeecke Feb 14, 2025

Replies: 1 comment

Uh oh!

Uh oh!

projectgus Feb 17, 2025 Collaborator

saraverbeecke
Feb 14, 2025

projectgus
Feb 17, 2025
Collaborator