Arm startup file tutorial

If we were not able to divide our projects into files and modules, we would be stuck with a single file with a million lines of code! Good luck maintaining that kinda code! It does this function by simply taking all the.

It does the same for. Now after Linker is done with our code we have a huge million line code file made up of opcodes for the machine to read and execute! Now that we have a single binary, we need to somehow organize the information present inside it so that it is compatible with what our microcontroller is expecting. Microcontrollers of different sizes have different memory maps associated with them.

The screenshot below shows the memory map of the STM32F microcontroller. It is the duty of the locator to stamp the correct addresses to the. In all microcontroller projects there is usually a special file called startup file. Once the microcontrollers are powered ON, they are hardwired to go to a predefined location and start running the code from there.

Usually, this location is the address 0x and this is the location where the startup code lives. The duty of the startup code is to take the machine from power-on point to the point where the main function starts executing the application code. Between power-on and main function starting, a number of important initializations are made which include the following.

During the locating process this startup code must be placed at address 0x and all the sections must be labeled with correct addresses so that the microcontroller can do the rest! On PCs the operating system does this step at the time the program is loaded and run also known as loading time.

This is the next step, load the damn binary onto the flash!! To load the program onto the flash and to debug microcontrollers come with a special peripheral known as the debug controller. Each of these protocols can be thought of as a different signaling language. Your PC can speak none of these languages and hence we need to do some translation again!

This time in terms of electrical signals. This is where USB debug adapters come into the picture. This is again done with the help of the debug controller and the adapter. Other than stepping through the code we can also set and clear breakpoints, read the memory contents of the microcontroller and other such debugging activities.

Once extracting the archive I was presented with a folder and inside the folder, I got all the goodies as shown in the screenshot below. Second,it helps deepen your understanding about the Cortex-M architecture. After reading this post, you will get to know how the ARM Cortex-M processor starts executing on power up. This post was originally published in ARM Community. Remember that this startup code is completely in assembly language. This blog post contains brief explanation of the syntax and code involved.

If you would like to go deeper in assembly programming, then the ARM assembler user guide is your best friend. Stack is an area used for temporary storage of variables and register contents during code execution.

EQU is an assembler directive. It is similar to the define pre-processor directive in C. The AREA directive divides the assembly code in different sections. This directive denotes a separate section in the memory. STACK in this case is the name of the section. Followed by the section name are some attributes for this section. This line allocates a space of 0x bytes in the stack area.

SPACE is an assembly directive. It reserves a space in memory for specified number of bytes. The vector table stores this value as the first entry. This label will equate to the next address after the stack space in this area. Since the stack grows downwards, this serves as the initial stack pointer.

This is where the processor locates point of entry to your application code. The attribute DATA indicates that this section will contain data and not instructions. This is true because the vector table contains only the addresses of the handlers and initial stack pointer value. This makes sure that the application code is not able to overwrite this area. This places the vector table at offset 0. Declaration of the Stack area The stack is a contiguous area of memory that may be used for storage of local variables and for passing additional arguments to subroutines when there are insufficient argument registers available.

Vector table The vector table contains the reset value of the stack pointer, and the start addresses for all exception and interrupt handlers. Assembler code of Reset handler After defining the vector table, we will discuss about the reset handler in the text segment. Definition of interrupt handler During the code execution, there might be exception or interrupt occurs, and the processor will start executing the exception or interrupt handler.

Information Title. Understand the GNU assembler startup file of cortex M4. URL Name. Sort by:. Search this feed Skip Feed Nothing here yet? Follow Following Unfollow. Show actions for this object. Drop Files. Upload Files Or drop files. Number of Views Number of Views 1K.