bx

Branch and Exchange

BX<c> <Rm>

Branches to address in register, optionally switching ISA.

Pseudocode Operation

if ConditionPassed() then
  new_PC ← Rm & 0xFFFFFFFE
  if (Rm & 1) == 1 then
    CPSR.T ← 1
  else
    CPSR.T ← 0
  BranchWritePC(new_PC)

Example

BX r2

Encoding

Binary Layout

cond

31:28

00010010

27:20

1

19

1

18

1

17

1

16

1

15

1

14

1

13

1

12

1

11

1

10

1

9

1

8

0001

7:4

Rm

3:0

 

Format Branch

Opcode 0x012FFF10

Extension A32 (Base)

Operands

• Rm
  Target Reg

Related

More in A32 (Base)

Reference

View in Arm A64 ISA Reference ↗ Arm AArch32 ISA

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0x012FFF10	BX{<c>}{<q>} <Rm>		A32		cond | 00010010 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0001 | Rm
0x4700	BX{<c>}{<q>} <Rm>		T32		01000111 | 0 | Rm | 0 | 0 | 0

Description

Branch and Exchange causes a branch to an address and instruction set specified by a register.

Operation

if ConditionPassed() then
    EncodingSpecificOperations();
    BXWritePC(R[m], BranchType_INDIR);