PM0215 datasheet(56/91 Pages) STMICROELECTRONICS

56 / 91 page

The STM32 Cortex-M0 instruction set

PM0215

56/91

Doc ID 022979 Rev 1

3.5.7

REV, REV16, and REVSH

Reverse bytes and reverse bits.

Syntax

op Rd, Rn

where:

●

‘op’ is one of:

REV: Reverse byte order in a word

REV16: Reverse byte order in each halfword independently

REVSH: Reverse byte order in the bottom halfword, and sign extends to 32 bits

●

‘Rd’ is the destination register

●

‘Rn’ is the register holding the operand

Operation

Use these instructions to change endianness of data:

●

REV: Converts either:

–

32-bit big-endian data into little-endian data or

–

32-bit little-endian data into big-endian data.

●

REV16: Converts either:

–

2 packed 16-bit big-endian data into little-endian data or

–

2 packed 16-bit little-endian data into big-endian data.

●

REVSH: Converts either:

–

16-bit signed big-endian data into 32-bit signed little-endian data or

–

16-bit signed little-endian data into 32-bit signed big-endian data

Restrictions

In these instructions, Rd, and Rn must only specify R0-R7.

Condition flags

These instructions do not change the flags.

Examples

REV R3, R7

; reverse byte order of value in R7 and write it to R3

REV16 R0, R0 ; reverse byte order of each 16-bit halfword in R0

REVSH R0, R5 ; reverse Signed Halfword

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