Datasheet

SAM3X / SAM3A [DATASHEET]
Atmel-11057C-ATARM-SAM3X-SAM3A-Datasheet_23-Mar-15
134
10.17.1 B, BL, BX, and BLX
Branch instructions.
10.17.1.1 Syntax
B{cond} label
BL{cond} label
BX{cond} Rm
BLX{cond} Rm
where:
B is branch (immediate).
BL is branch with link (immediate).
BX is branch indirect (register).
BLX is branch indirect with link (register).
cond is an optional condition code, see “Conditional execution” on page 91.
label is a PC-relative expression. See “PC-relative expressions” on page 90.
Rm is a register that indicates an address to branch to. Bit[0] of the value in Rm must be 1, but the
address to branch to is created by changing bit[0] to 0.
10.17.1.2 Operation
All these instructions cause a branch to label, or to the address indicated in Rm. In addition:
 The BL and BLX instructions write the address of the next instruction to LR (the link register, R14).
 The BX and BLX instructions cause a UsageFault exception if bit[0] of Rm is 0.
Bcond label is the only conditional instruction that can be either inside or outside an IT block. All other branch
instructions must be conditional inside an IT block, and must be unconditional outside the IT block, see “IT” on
page 137.
Table 10-24 shows the ranges for the various branch instructions.
You might have to use the .W suffix to get the maximum branch range. See “Instruction width selection” on page
92.
10.17.1.3 Restrictions
The restrictions are:
 do not use PC in the BLX instruction
 for BX and BLX, bit[0] of Rm must be 1 for correct execution but a branch occurs to the target address
created by changing bit[0] to 0
 when any of these instructions is inside an IT block, it must be the last instruction of the IT block.
Table 10-24. Branch ranges
Instruction Branch range
B label −16 MB to +16 MB
B cond label (outside IT block) −1 MB to +1 MB
B cond label (inside IT block) −16 MB to +16 MB
BL{cond} label −16 MB to +16 MB
BX{cond} Rm Any value in register
BLX{cond} Rm Any value in register