A simple arm program question, could help me?

After executing the instructon bl read_nand_to_sdram, my arm program will not execute the instruction ldr sp,=0x34000000 , but goback to execute the instruction bl init_sdram,why?

  .global _start
   .text
_start:
  ldr sp,=4095
  bl  init_sdram     
  bl  read_nand_to_sdram
  ldr sp,=0x34000000
  ldr lr,=loop
  ldr pc,=main
loop:
  b loop