Hello sir,
I have 6+ years of experience in embedded and iot system development. And I had developed bootloader using UART, wifi, ble, sdcard, usb for nRF51/52, PSoC4/6, STM32F0/1/2/4, SAMD21 etc.
I had even developed a encrypted bootloader for secure deployment of OTA.
let's have a chat to discuss it in details