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JBond.1
JBond.1
Senior
October 8, 2023
Solved

STM32F4 using CCM data RAM for STACK and HEAP

  • October 8, 2023
  • 2 replies
  • 5205 views

Hi, I have STM32F407VET6 which has such memory layout.

0693W00000YA0E4QAL.png

As I understand CCM data RAM is unused by default and just waits to be used? So can I move STACK and HEAP to it? How do I move it? (I did not find defined STACK address anywhere in KEIL project)

Is there anything else I could use CCM for?

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Best answer by waclawek.jan

In 'F4, I personally place both stack and all "normal" data (.data, .bss) into CCM. Into SRAM I then place communication buffers and other "large" structures (e.g. DMA can't work with CCM), so only those need to be tagged. I guess heap would fall into this "large" cathegory, except I refrain from using dynamic allocation in microcontrollers.

I don't use Keil so can't help with the particularities, but I am sure the manual to compiler/IDE explains how to locate the variables (IIRC Keil calls the linker script "scatter file" so that might be a starting point to search).

JW

2 replies

waclawek.jan
waclawek.janBest answer
Super User
October 8, 2023

In 'F4, I personally place both stack and all "normal" data (.data, .bss) into CCM. Into SRAM I then place communication buffers and other "large" structures (e.g. DMA can't work with CCM), so only those need to be tagged. I guess heap would fall into this "large" cathegory, except I refrain from using dynamic allocation in microcontrollers.

I don't use Keil so can't help with the particularities, but I am sure the manual to compiler/IDE explains how to locate the variables (IIRC Keil calls the linker script "scatter file" so that might be a starting point to search).

JW

    JBond.1
    JBond.1Author
    Senior
    October 8, 2023

    Do you mean like this:

     

    ; *************************************************************
; *** Scatter-Loading Description File for STM32F4 ***
; *************************************************************

LR_IROM1 0x08004000 0x0007C000 { ; load region size_region
 ER_IROM1 0x08004000 0x0007C000 { ; load address = execution address
 *.o (RESET, +First)
 *(InRoot$$Sections)
 .ANY (+RO)
 .ANY (+XO)
 }
 RW_IRAM1 0x20000000 0x0001C000 { ; RW data
 .ANY (SRAM)
 ;.ANY (+RW +ZI)
 }
 RW_IRAM2 0x2001C000 0x00004000 {
 .ANY (SRAM2)
 ;.ANY (+RW +ZI)
 }
 RW_IRAM3 0x10000000 0x00010000 { ; CCM data
 .ANY (+RW +ZI)
 startup_stm32f407xx.o (STACK)
 startup_stm32f407xx.o (HEAP)
 }
}

     

    "+RW +ZI, STACK, HEAP" - in CCM?
    "+RW +ZI" is so called "normal" data (.data, .bss)?

    And then lange buffers
    static uint8_t Cache[CACHE_SIZE] __attribute__ ((section("SRAM")));
    ?

    JBond.1
    JBond.1Author
    Senior
    October 8, 2023

    I found how to do it in KEIL. Need to go to:
    Options for target 'project name' -> Linker -> uncheck Use Memory Layout from Target Dialog.
    After that its possible to edit "Scatter file" in same window. In it I have added:

     

    RW_IRAM3 0x10000000 0x00010000 { ; CCM data
 .ANY (CCM_DATA)
 startup_stm32f407xx.o (STACK)
 startup_stm32f407xx.o (HEAP)
 }

     

    But I guess your approach is better to place everything to CCM and only large buffers, DMA buffers to SRAM.

     

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