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embeddedavr

Error "Relative branch out of reach" in avr

I'm new on AVR. I have an "Relative branch out of reach" error for the "brne round_loop" line while debugging. Is anyone to help me? Thank you so much for your helps.

; Test if round counter has reached 14
mov     t4, rc
subi    t4, 14
brne    round_loop

round_loop:

round_loop:
; XOR state and key
eor     s0, k0
eor     s1, k1
eor     s2, k2
eor     s3, k3
Solution

  • The AVR BRNE instruction is a 16 bit op-code, 7 bits of which are the branch offset. This 7 bit signed operand can have a value k in the range -64 ≤ k ≤ +63. The PC is modified by k +1 (i.e. -63 to +64). If the jump is further then that, a relative branch is unsuitable.

    You either need to locate the target closer to the branch, or use an unconditional branch to an unconditional jump (JMP) with a 22bit range, or a relative jump (RJMP) with a 12 bit range.

      mov     t4, rc
  subi    t4, 14

  brne    round_loop_longjmp
  rjmp    no_round_jmp
round_loop_longjmp:
  rjmp    round_loop

no_round_jmp:
  ...