What is Boot Loader?

All firmware developers listens the word BOOT LOADER. There is little bit confusion with this word in contrast to PC and Microcontroller.

In contrast to PC boot loader is a program that runs before an operation system start. Boot loader places the operating system in memory.  In computer is the process of initialization of all the peripherals.  

In microcontroller boot loader is the small piece of code which is used to reprogram the flash program memory. Boot loader resides in the program memory. Boot loader code should be small in size. Boot loader code may be place at the bottom of Flash Memory or at Top of Flash memory. Boot loader receives the code from any external communication module such as USB, UART, SPI, I2C, CAN etc and save this code in to program memory.

As shown in figure above after reset program start executing from Reset Vector 0x0000h. The Boot Load Code is available at bottom of Flash Memory.

Why Use Boot Loader?

·        Mostly microcontrollers use special hardware to program microcontroller. For example ST’s Microcontroller uses JTAG or single Interface module, AVR uses JTAG interface to program and debugging. They have some pins for programming. The hex file is of program originates in PC, So hardware to program the microcontroller is connected to PC by some interface like USB and Serial Communication and other end connected with the Microcontroller.  Some time this hardware is very expensive. In some cases Microcontrollers will be programmed with boot loader code with special hardware devices. Boot Loader code check communicates with host system through some type of communication like UART and if it gets any firmware upgrade command from Host system it will update the firmware of Microcontroller else it will execute existing code.

·        In Some case it is required to Firmware update in field then Boot Loader come in existence. In that cases Hex file will place in PC or other device which will communicates with microcontroller through serial communication.  When Microcontrollers get Reset command either by hardware or software, after reset boot loader check communication with Host system to upgrade the Firmware.

·        Firmware update over the air is the place where Boot Loader is required.  In this case we save the program to be updated receives from wireless communication in external memory or internal flash memory. After saving program we give the software reset command to microcontroller. After reset if new program exists in flash memory boot loader set program counter to execute program from new location.  If program saves in external memory then boot loader will first update the program in controller flash memory and then start execution updated program.