[U-Boot] Regarding Start.S file

[Asmit Patel]

Hi All,
I am new to u-boot and ARM. I am trying to understand uboot thtough start.S
file.
I have few questions about it.
1) What is the deifference between ARM Supervisior and User mode. why uboot
is not running in user mode?
2) At the start of startup file I found below code.

 .globl _start
 _start: b start_code
ldr pc, _undefined_instruction
 ldr pc, _software_interrupt
 ldr pc, _prefetch_abort
ldr pc, _data_abort
ldr pc, _not_used
ldr pc, _irq
ldr pc, _fiq

_undefined_instruction: .word undefined_instruction
_software_interrupt: .word software_interrupt
 _prefetch_abort: .word prefetch_abort
_data_abort: .word data_abort
 _not_used: .word not_used
_irq: .word irq
 _fiq: .word fiq

 .balignl 16,0xdeadbeef


What is this code will do? as i believe the instruction "b start_code" will
branch it to start_code then how does the other code below branch
instruction will work?

3) where does exception vector table located during power on? on boot rom or
at any other place?


Thanks & Regards,
Asmit Patel"