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ATSAM4S-XPLD
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SAM4S [DATASHEET]
11100E–ATARM–24-Jul-13
12.6.10.3IT
If-Then condition instruction.
Syntax
IT{x{y{z}}} cond
where:
x
specifies the condition switch for the second instruction in the IT block.
y
specifies the condition switch for the third instruction in the IT block.
z
specifies the condition switch for the fourth instruction in the IT block.
cond
specifies the condition for the first instruction in the IT block.
The condition switch for the second, third and fourth instruction in the IT block can be either:
T
Then. Applies the condition cond to the instruction.
E
Else. Applies the inverse condition of cond to the instruction.
It is possible to use AL (the always condition) for cond in an IT instruction. If this is done, all of the instructions in the IT
block must be unconditional, and each of x, y, and z must be T or omitted but not E.
block must be unconditional, and each of x, y, and z must be T or omitted but not E.
Operation
The IT instruction makes up to four following instructions conditional. The conditions can be all the same, or some of
them can be the logical inverse of the others. The conditional instructions following the IT instruction form the IT block.
them can be the logical inverse of the others. The conditional instructions following the IT instruction form the IT block.
The instructions in the IT block, including any branches, must specify the condition in the {cond} part of their syntax.
The assembler might be able to generate the required IT instructions for conditional instructions automatically, so that the
user does not have to write them. See the assembler documentation for details.
user does not have to write them. See the assembler documentation for details.
A BKPT instruction in an IT block is always executed, even if its condition fails.
Exceptions can be taken between an IT instruction and the corresponding IT block, or within an IT block. Such an
exception results in entry to the appropriate exception handler, with suitable return information in LR and stacked PSR.
exception results in entry to the appropriate exception handler, with suitable return information in LR and stacked PSR.
Instructions designed for use for exception returns can be used as normal to return from the exception, and execution of
the IT block resumes correctly. This is the only way that a PC-modifying instruction is permitted to branch to an
instruction in an IT block.
the IT block resumes correctly. This is the only way that a PC-modifying instruction is permitted to branch to an
instruction in an IT block.
Restrictions
The following instructions are not permitted in an IT block:
IT
CBZ and CBNZ
CPSID and CPSIE.
Other restrictions when using an IT block are:
A branch or any instruction that modifies the PC must either be outside an IT block or must be the last instruction
inside the IT block. These are:
inside the IT block. These are:
ADD PC, PC, Rm
MOV PC, Rm
B, BL, BX, BLX
Any LDM, LDR, or POP instruction that writes to the PC
TBB and TBH
Do not branch to any instruction inside an IT block, except when returning from an exception handler
All conditional instructions except Bcond must be inside an IT block. Bcond can be either outside or inside an IT
block but has a larger branch range if it is inside one
block but has a larger branch range if it is inside one
Each instruction inside the IT block must specify a condition code suffix that is either the same or logical inverse as
for the other instructions in the block.
for the other instructions in the block.