PM0214 datasheet(144/245 Pages) STMICROELECTRONICS

144 / 245 page

The STM32 Cortex-M4 instruction set

PM0214

144/245

DocID022708 Rev 4

3.9.7

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.

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.

The instructions in the IT block, including any branches, must specify the condition in the

{cond} part of their syntax.

Your assembler might be able to generate the required IT instructions for conditional

instructions automatically, so that you do not need to write them yourself. See your

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.

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.

Restrictions

The following instructions are not permitted in an IT block:

•

CBZ and CBNZ

•

CPSID and CPSIE.

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