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SAM4CP [DATASHEET]
43051E–ATPL–08/14
12.6.10.1 B, BL, BX, and BLX
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
is an optional condition code, see
“Conditional Execution”
.
label
is a PC-relative expression. See
“PC-relative Expressions”
.
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.
B
cond
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”
.
The table below shows the ranges for the various branch instructions.
The .W suffix might be used to get the maximum branch range. See
“Instruction Width Selection”
.
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.
B
cond
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
These instructions do not change the flags.
Table 12-26. Branch Ranges
Instruction
Branch Range
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