carlogravador / gnu-tools-baremetal-practice

Star-up file

• Responsible for setting up right environment for the main user code to run.

Contents of Startup file

1. Create a vector table for your microcontroller. Vector table are MCU specific
2. Write a start-up code which initializes .data .bss section in SRAM
3. Call main()

• Vector Table - contains handler addresses Search for your MCU's reference manual

Creating a Vector Table

Code memory (Flash)

------------------
Unused Code memory
------------------
.data
(initialized
global and static
variables)
-------------------
.rodata
-------------------
.text
-------------------                         ----------------------------
Vector Table          ------------------->     Addr of IRQ-N Handler 
-------------------                         ----------------------------
                                              Addr of IRQ-(N-1) Handler
                                            ----------------------------
                                                          .
                                                          .
                                                          .

                                            ----------------------------
                                                  Addr of IRQ-1 Handler
                                            ----------------------------
                                                  Initial MSP Value
                                            ----------------------------

1. Create an array to hold MSP and handlers addresses.

uint32_t vectors[] = {store MSP and address of various handlers here}

MSP - main stack pointer (first word in the vector table)

2. Instruct the compiler no to include the above array in .data but in a user defined section

Linker Scripts

• Explains how different sections of the object files should be merged to create an output file
• must be supply during linking phase

VMA - virtual memory address LMA - load memory address

Location Counter always tracks vma of the section in whic it is being used