bootloader entry

	void (*SysMemBootJump)(void);
	volatile uint32_t addr = 0x1FFF0000;
	/* Jump to the built in bootloader by mapping System flash */
	rcc_peripheral_enable_clock(&RCC_APB2ENR, RCC_APB2ENR_SYSCFGEN);
	SYSCFG_MEMRM &= ~3;
	SYSCFG_MEMRM |=  1;
	/*
	 set the jump address
	 */
	SysMemBootJump = (void (*)(void)) (*((uint32_t *) (addr + 4)));
	/*
	 set up the stack for the bootloader
	 */
	asm ("ldr sp, =addr");
	/*
	 Jump ...
	 */
	SysMemBootJump ();
	while ( 1 );