[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"