how to reserve memory segment using SES

[Allen]

Hello,

I have modified flash_placement.xml to define a 64 byte RAM region to be used to preserve data across soft resets. It compiles and links but the memory seems to be set to zeros on reset initialization.

This is part of flash_placement.xml. (I have tried load="No" as well)

    <ProgramSection alignment="4" load="No" name=".tbss" />
    <ProgramSection alignment="4" load="No" name=".non_init" />
    <ProgramSection alignment="8" keep="Yes" size="$(EWAVE_DATA_SIZE)" load="Yes" name=".ewave"/>
    <ProgramSection alignment="4" size="__HEAPSIZE__" load="No" name=".heap" />
    <ProgramSection alignment="8" size="__STACKSIZE__" load="No" place_from_segment_end="Yes" name=".stack"  address_symbol="__StackLimit" end_symbol="__StackTop"/>
    <ProgramSection alignment="8" size="__STACKSIZE_PROCESS__" load="No" name=".stack_process" />

This is the map file output:

                0x0000000020007128                __ewave_load_start__ = ALIGN (__non_init_end__, 0x8)

.ewave          0x0000000020007128       0x40
                0x0000000020007128                __ewave_start__ = .
 *(.ewave .ewave.*)
                0x0000000020007168                . = ALIGN (MAX ((__ewave_start__ + 0x40), .), 0x8)
 *fill*         0x0000000020007128       0x40 
                0x0000000020007168                __ewave_end__ = (__ewave_start__ + SIZEOF (.ewave))
                0x0000000000000040                __ewave_size__ = SIZEOF (.ewave)
                0x0000000020007168                __ewave_load_end__ = __ewave_end__
                0x0000000000000001                . = ASSERT (((__ewave_start__ == __ewave_end__) || ((__ewave_end__ - __RAM1_segment_start__) <= __RAM1_segment_size__)), error: .ewave is too large to fit

It appears it is defined to be *filled* and I don't know how to disable that.

TIA

[Vidar Berg]

Hello,

I'm not seeing any problems with the way you have defined your linker section.  Did you by any chance have a bootloader present when testing this? In that case, maybe the bootloader is overwriting your section after reset?

It appears it is defined to be *filled* and I don't know how to disable that.

*Fill* is the unused part of your section, but it does not actually fill any data unless you also modify the startup file (thumb_crt0.s) to do so. And it will go away if you don't specify a fixed  "size" for the section in your flash_placement.xml.

This is the code I used to test here:

#define MAGIC_WORD    0x51B1E5DB

typedef struct 
{
    uint32_t magic_word;
    uint32_t value;
} boot_count_t;


__attribute__((section(".ewave"))) static boot_count_t boot_count;


/**@brief Application main function.
 */
 
int main(void)
{
    bool erase_bonds;

    log_init();

    if (boot_count.magic_word != MAGIC_WORD)
    {
      boot_count.magic_word = MAGIC_WORD;
      boot_count.value = 0x0;
    }
    else
    {
        boot_count.value++;
        NRF_LOG_INFO("Boot count: %d", boot_count.value);
        NRF_LOG_PROCESS();
    }
    
    nrf_delay_ms(100);
    /* Reboot */
    NVIC_SystemReset();

and flash_placement:

Best regards,

Vidar