Can I change the system bootloader program so that it can be customized according to my application (Actually I want the stm32 system bootloader to take HEX file from my external EEPROM and write it into controller Flash). For this purpose I need to know how to replace original system bootloader and update it to do my above task. Can I change original system bootloader or not? Where is the source code of it and how to change it? I know that there is ST IAP help but this method uses Flash memory to first include IAP drive and then user application is programmed through it but it never uses system bootloader. I want to save memory used by IAP. How can I perform my above task of programming HEX file from EEPROM?