Startup sequence and reset vector in Embedded C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the reset vector in embedded systems?

The reset vector is the specific memory address where the processor starts executing code after a reset. It points to the startup code that initializes the system.

beginner

Describe the startup sequence in an embedded system.

The startup sequence is the set of steps the processor follows after reset, including setting the stack pointer, initializing data and bss sections, and then calling the main program.

intermediate

Why is the stack pointer initialized early in the startup sequence?

The stack pointer is set early to ensure that function calls and local variables have a safe place in memory to work with during program execution.

intermediate

What happens to the .data and .bss sections during startup?

The .data section is copied from flash to RAM to initialize variables with predefined values, while the .bss section is cleared to zero to initialize uninitialized variables.

beginner

How does the processor know where to find the reset vector?

The processor has a fixed memory location, often at the start of memory, reserved for the reset vector. On reset, it reads this address to jump to the startup code.

What is the first action the processor takes after a reset?

A Clear the stack pointer

B Initialize all variables

C Start executing main() directly

D Jump to the reset vector address

After reset, the processor jumps to the reset vector address to start the startup sequence.

During startup, what is the purpose of copying the .data section from flash to RAM?

A To start the main program

B To initialize variables with predefined values

C To set the stack pointer

D To clear all variables to zero

The .data section contains variables with initial values stored in flash; copying it to RAM sets those variables correctly.

What does the .bss section contain before startup?

A Uninitialized variables

B Initialized variables

C Code instructions

D Stack data

The .bss section holds uninitialized variables that are set to zero during startup.

Why must the stack pointer be set before calling main()?

A To provide space for function calls and local variables

B To initialize global variables

C To reset the processor

D To copy the .data section

The stack pointer defines where the stack starts, which is needed for function calls and local variables.

Where is the reset vector usually located?

A At the end of RAM

B Inside the main() function

C At a fixed memory address at the start of memory

D In the .bss section

The reset vector is stored at a fixed address so the processor knows where to jump after reset.

Explain the steps the processor takes from reset to starting the main program.

Think about what needs to be ready before main() runs.

Describe the role of the reset vector in the startup sequence.

It is the first instruction address after reset.