Atmel ARM-Based Evaluation Kit for SAM4S16C, 32-Bit ARM® Cortex® Microcontroller ATSAM4S-WPIR-RD ATSAM4S-WPIR-RD Data Sheet

SAM4S Series [DATASHEET]

Atmel-11100G-ATARM-SAM4S-Datasheet_27-May-14

180

Branch instructions.
Syntax

B{cond} label

BL{cond} label

BX{cond} Rm

BLX{cond} Rm

where:
Bis branch (immediate).
BLis branch with link (immediate).
BXis branch indirect (register).
BLXis branch indirect with link (register).
condis an optional condition code, see 

.

labelis a PC-relative expression. See 

Rmis 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.
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 result in 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 

The table below shows the ranges for the various branch instructions.

 

The .W suffix might be used to get the maximum branch range. See 

.

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.

 

Bcond is the only conditional instruction that is not required to be inside an IT block. However, it has a longer 

branch range when it is inside an IT block.

B label

−16 MB to +16 MB

Bcond label (outside IT block)

−1 MB to +1 MB

Bcond 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