2.6.4.2.3 Restrictions

For load instructions:

  • Rt can be SP or PC for word loads only
  • Rt must be different from Rt2 for two-word loads
  • Rn must be different from Rt and Rt2 in the pre-indexed or post-indexed forms.

When Rt is PC in a word load instruction:

  • bit[0] of the loaded value must be 1 for correct execution
  • a branch occurs to the address created by changing bit[0] of the loaded value to 0
  • if the instruction is conditional, it must be the last instruction in the IT block.

For store instructions:

  • Rt can be SP for word stores only
  • Rt must not be PC
  • Rn must not be PC
  • Rn must be different from Rt and Rt2 in the pre-indexed or post-indexed forms.