question regarding startup code

Hi ppl,
Am a newbie to u-boot as well as arm assembly.
wanted to know about the startup code. Below is the vector table pasted from the code. What i dont understand is why only the reset vector is PC relative and all others have memory allocated to hold the addresses. I mean all other vectors also could be branch instructions.Any reason ?

.globl _start
_start: b reset
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

Thanks and Regards,
Srinivas Bakki

      __________________________________________________________

Sent from Yahoo! Mail.
More Ways to Keep in Touch. http://uk.docs.yahoo.com/nowyoucan.html

Hi,
I have thought of an explanation can anyone please
rectify if am wrong.

the load to PC instruction allows utilizing the full 32-bit address space for placement of the exception handlers, whereas the relative branch instruction is limited to +/- 25 bits relative to the current PC.

is that right ?

Regards,
Srinivas Bakki

      __________________________________________________________

Sent from Yahoo! Mail.
More Ways to Keep in Touch. http://uk.docs.yahoo.com/nowyoucan.html

Srinivas

Try

http://infocenter.arm.com
Software Development Toolkit
ARM Software Development Toolkit User Guide
10. Writing Code For ROM

Let me know offlist if you can't access this.

Regards

Peter