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How to run an application fully from within RAM (for Bootloader self-update)?

Question asked by CaCO3.CaCO3 on Mar 14, 2017

Hi

I have written a bootloader which is able to update an application and/or start it.

This works as required.

 

Now I am on the task to be able to update the bootloader itself.

To do so, my understanding is that the bootloader needs to be copied to the RAM from within the startup code ( eg. __initialize_hardware_early() ) and then run from there?

 

I expect that I have to change something in the startup code in __initialize_hardware.c, system_stm32f7xx.c and the linker script.

They all are generated by CubeMX respectively GNU ARM Eclipse (http://gnuarmeclipse.github.io/ ).

 

The generated (and a bit simplified) linker script looks like this:

/*
* Default linker script for Cortex-M (it includes specifics for STM32F[34]xx).
*
* To make use of the multi-region initialisations, define
* OS_INCLUDE_STARTUP_INIT_MULTIPLE_RAM_SECTIONS for the _startup.c file.
*/


/*
* The '__stack' definition is required by crt0, do not remove it.
*/

__stack = ORIGIN(RAM) + LENGTH(RAM);

_estack = __stack;      /* STM specific definition */

/*
* Default stack sizes.
* These are used by the startup in order to allocate stacks
* for the different modes.
*/


__Main_Stack_Size = 1024 ;

PROVIDE ( _Main_Stack_Size = __Main_Stack_Size ) ;

__Main_Stack_Limit = __stack  - __Main_Stack_Size ;

/* "PROVIDE" allows to easily override these values from an
* object file or the command line. */

PROVIDE ( _Main_Stack_Limit = __Main_Stack_Limit ) ;

/*
* There will be a link error if there is not this amount of
* RAM free at the end.
*/

_Minimum_Stack_Size = 256 ;

/*
* Default heap definitions.
* The heap start immediately after the last statically allocated
* .sbss/.noinit section, and extends up to the main stack limit.
*/

PROVIDE ( _Heap_Begin = _end_noinit ) ;
PROVIDE ( _Heap_Limit = __stack - __Main_Stack_Size ) ;

/*
* The entry point is informative, for debuggers and simulators,
* since the Cortex-M vector points to it anyway.
*/

ENTRY(_start)


/* Sections Definitions */

SECTIONS
{
    /*
     * For Cortex-M devices, the beginning of the startup code is stored in
     * the .isr_vector section, which goes to FLASH.
     */

    .isr_vector : ALIGN(4)
    {
        FILL(0xFF)
       
        __vectors_start = ABSOLUTE(.) ;
        __vectors_start__ = ABSOLUTE(.) ; /* STM specific definition */
        KEEP(*(.isr_vector))          /* Interrupt vectors */
       
          KEEP(*(.cfmconfig))               /* Freescale configuration words */  
              
        /*
         * This section is here for convenience, to store the
         * startup code at the beginning of the flash area, hoping that
         * this will increase the readability of the listing.
         */

        *(.after_vectors .after_vectors.*)     /* Startup code and ISR */

    } >FLASH

    .inits : ALIGN(4)
    {
        /*
         * Memory regions initialisation arrays.
         *
         * Thee are two kinds of arrays for each RAM region, one for
         * data and one for bss. Each is iterrated at startup and the  
         * region initialisation is performed.
         *
         * The data array includes:
         * - from (LOADADDR())
         * - region_begin (ADDR())
         * - region_end (ADDR()+SIZEOF())
         *
         * The bss array includes:
         * - region_begin (ADDR())
         * - region_end (ADDR()+SIZEOF())
         *
         * WARNING: It is mandatory that the regions are word aligned,
         * since the initialisation code works only on words.
         */

        
        __data_regions_array_start = .;
       
        LONG(LOADADDR(.data));
        LONG(ADDR(.data));
        LONG(ADDR(.data)+SIZEOF(.data));
       
        LONG(LOADADDR(.data_CCMRAM));
        LONG(ADDR(.data_CCMRAM));
        LONG(ADDR(.data_CCMRAM)+SIZEOF(.data_CCMRAM));
       
        __data_regions_array_end = .;
       
        __bss_regions_array_start = .;
       
        LONG(ADDR(.bss));
        LONG(ADDR(.bss)+SIZEOF(.bss));
       
        LONG(ADDR(.bss_CCMRAM));
        LONG(ADDR(.bss_CCMRAM)+SIZEOF(.bss_CCMRAM));
       
        __bss_regions_array_end = .;

        /* End of memory regions initialisation arrays. */
   
        /*
         * These are the old initialisation sections, intended to contain
         * naked code, with the prologue/epilogue added by crti.o/crtn.o
         * when linking with startup files. The standalone startup code
         * currently does not run these, better use the init arrays below.
         */

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

          . = ALIGN(4);

          /*
         * The preinit code, i.e. an array of pointers to initialisation
         * functions to be performed before constructors.
         */

          PROVIDE_HIDDEN (__preinit_array_start = .);
       
        /*
         * Used to run the SystemInit() before anything else.
         */

          KEEP(*(.preinit_array_sysinit .preinit_array_sysinit.*))
       
        /*
         * Used for other platform inits.
         */

          KEEP(*(.preinit_array_platform .preinit_array_platform.*))
       
        /*
         * The application inits. If you need to enforce some order in
         * execution, create new sections, as before.
         */

          KEEP(*(.preinit_array .preinit_array.*))

          PROVIDE_HIDDEN (__preinit_array_end = .);

          . = ALIGN(4);

          /*
         * The init code, i.e. an array of pointers to static constructors.
         */

          PROVIDE_HIDDEN (__init_array_start = .);
          KEEP(*(SORT(.init_array.*)))
          KEEP(*(.init_array))
          PROVIDE_HIDDEN (__init_array_end = .);

          . = ALIGN(4);

          /*
         * The fini code, i.e. an array of pointers to static destructors.
         */

          PROVIDE_HIDDEN (__fini_array_start = .);
          KEEP(*(SORT(.fini_array.*)))
          KEEP(*(.fini_array))
          PROVIDE_HIDDEN (__fini_array_end = .);

    } >FLASH

    /*
     * For some STRx devices, the beginning of the startup code
     * is stored in the .flashtext section, which goes to FLASH.
     */

    .flashtext : ALIGN(4)
    {
        *(.flashtext .flashtext.*)     /* Startup code */
    } >FLASH

   
    /*
     * The program code is stored in the .text section,
     * which goes to FLASH.
     */

    .text : ALIGN(4)
    {
        *(.text .text.*)               /* all remaining code */

          /* read-only data (constants) */
        *(.rodata .rodata.* .constdata .constdata.*)           

        *(vtable)                         /* C++ virtual tables */

          KEEP(*(.eh_frame*))

          /*
           * Stub sections generated by the linker, to glue together
           * ARM and Thumb code. .glue_7 is used for ARM code calling
           * Thumb code, and .glue_7t is used for Thumb code calling
           * ARM code. Apparently always generated by the linker, for some
           * architectures, so better leave them here.
           */

        *(.glue_7)
        *(.glue_7t)

    } >FLASH

     /* ARM magic sections */
     .ARM.extab : ALIGN(4)
        {
       *(.ARM.extab* .gnu.linkonce.armextab.*)
        } > FLASH
        
    . = ALIGN(4);
        __exidx_start = .;        
        .ARM.exidx : ALIGN(4)
        {
       *(.ARM.exidx* .gnu.linkonce.armexidx.*)
        } > FLASH
        __exidx_end = .;
        
    . = ALIGN(4);
    _etext = .;
    __etext = .;
   
    /* MEMORY_ARRAY */
    /*
    .ROarraySection :
    {
          *(.ROarraySection .ROarraySection.*)                         
    } >MEMORY_ARRAY
    */


     /*
      * The secondary initialised data section.
      */

    .data_CCMRAM : ALIGN(4)
    {
       FILL(0xFF)
       *(.data.CCMRAM .data.CCMRAM.*)
       . = ALIGN(4) ;
    } > CCMRAM AT>FLASH

     /*
     * This address is used by the startup code to
     * initialise the .data section.
     */

    _sidata = LOADADDR(.data);

    /*
     * The initialised data section.
     *
     * The program executes knowing that the data is in the RAM
     * but the loader puts the initial values in the FLASH (inidata).
     * It is one task of the startup to copy the initial values from
     * FLASH to RAM.
     */

    .data : ALIGN(4)
    {
         FILL(0xFF)
        /* This is used by the startup code to initialise the .data section */
        _sdata = . ;             /* STM specific definition */
        __data_start__ = . ;
          *(.data_begin .data_begin.*)

          *(.data .data.*)
          
          *(.data_end .data_end.*)
         . = ALIGN(4);

         /* This is used by the startup code to initialise the .data section */
        _edata = . ;             /* STM specific definition */
        __data_end__ = . ;

    } >RAM AT>FLASH
   
    /*
     * The uninitialised data sections. NOLOAD is used to avoid
     * the "section `.bss' type changed to PROGBITS" warning
     */

    
    /* The secondary uninitialised data section. */
     .bss_CCMRAM (NOLOAD) : ALIGN(4)
     {
          *(.bss.CCMRAM .bss.CCMRAM.*)
     } > CCMRAM

    /* The primary uninitialised data section. */
    .bss (NOLOAD) : ALIGN(4)
    {
        __bss_start__ = .;          /* standard newlib definition */
        _sbss = .;              /* STM specific definition */
        *(.bss_begin .bss_begin.*)

        *(.bss .bss.*)
        *(COMMON)
       
        *(.bss_end .bss_end.*)
         . = ALIGN(4);
        __bss_end__ = .;        /* standard newlib definition */
        _ebss = . ;             /* STM specific definition */
    } >RAM

    .noinit_CCMRAM (NOLOAD) : ALIGN(4)
    {
        *(.noinit.CCMRAM .noinit.CCMRAM.*)        
    } > CCMRAM
   
    .noinit (NOLOAD) : ALIGN(4)
    {
        _noinit = .;
       
        *(.noinit .noinit.*)
       
         . = ALIGN(4) ;
        _end_noinit = .;  
    } > RAM
   
    /* Mandatory to be word aligned, _sbrk assumes this */
    PROVIDE ( end = _end_noinit ); /* was _ebss */
    PROVIDE ( _end = _end_noinit );
    PROVIDE ( __end = _end_noinit );
    PROVIDE ( __end__ = _end_noinit );
   
    /*
     * Used for validation only, do not allocate anything here!
     *
     * This is just to check that there is enough RAM left for the Main
     * stack. It should generate an error if it's full.
     */

    ._check_stack : ALIGN(4)
    {
        . = . + _Minimum_Stack_Size ;
    } >RAM 
}

 

How would I have to start?

Is there any documentation/examples I could build on?

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