Where is the STM32F103 start code?

Depends on your tool chain. Look for a startup*.s assembler file in your STM232CubeMX generated project folder.

The startup code could also be written in C with some attributes like:

// Cortex-M startup code using gcc-none-eabi toolchain
#include <stdint.h>
#include <string.h>
 
// symbols provided by the .ld linker script file
extern uint32_t _etext;
extern uint32_t _sdata;
extern uint32_t _edata;
extern uint32_t _sidata;
extern uint32_t _sbss;
extern uint32_t _ebss;
extern uint32_t _estack;
 
extern int main(void);
 
#pragma GCC optimize("O3")
 
__attribute__ ((naked)) 
void Reset_Handler(void)
{
 // copy initialized global variables in .data from flash to SRAM
 memcpy(&_sdata, &_sidata, (size_t)&_edata - (size_t)&_sdata);
 
 // init uninitialized global variables in .bss with zero
 memset(&_sbss, 0, (size_t)&_ebss - (size_t)&_sbss);
 
 // now invoke main()
 main();
 
 // if main() returns:
 for (;;)
 ;
}
 
void* vectors[128] __attribute__((section(".isr_vector"))) = 
{
 &_estack,
 Reset_Handler,
 // more IRQ handlers go here
};

hth

KnarfB

Where i decide it is.

Your code fragment is just a right step on proper programming.

Second step would be using open source compiler, -nostdlib

to not waste stack put main in vectors instead of reset handler and then do

void __attribute__ ((noreturn)) main() {

system_init();

while(1) {

//main loop here;

}

}

and in system init do this memcpy, memset. I recommend to configure FLASH_ACR and then clocks first so it gets up to speed as soon as possible. Unless you want to run on lower than default clock then set up clock after init.

If you would make your own linker script stack definition could be much easier - just declare global variable with right section (like noinit).

Too i recommend to not abuse memcpy and memset. Make use of fact that both data and bss is 4 byte aligned at least - you may copy by words.

I like to put stack at beginning, not end of RAM (by defining section in linkerscript), as stack overflow would result in hard crash, not silent overwrite of global variables. But that's my preference.

Hi,

The code I mean is not my code, it is the code that after a reset load SP and PC with the values I put in address 0x00 and 0x04.

This code runs before my code, it is a kind of bootloader?

Thanks all for the answers, they helped me.