Code execution on Reset for ARM: info required

I want to write a program in assembly where my code is resident from location, say, 0x20000. On reset, code execution should start from location 0x20000. Kindly let us know how to write the initial code.

I tried the following:

AREA ARMex, CODE, AT 0x00000000
ENTRY

start
    B here
 org 0x20000

 here: MOV    r0, #10
    MOV     r1, #3
    ADD    r0, r0, r1
END