Atmel SAM4S-XPLD Atmel ATSAM4S-XPLD ATSAM4S-XPLD Hoja De Datos

 162

SAM4S [DATASHEET]

11100E–ATARM–24-Jul-13

Branch instructions.

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

label

.

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.

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.

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.

Condition Flags

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