PM0214 datasheet(100/245 Pages) STMICROELECTRONICS

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The STM32 Cortex-M4 instruction set

PM0214

100/245

DocID022708 Rev 4

3.5.17

UASX and USAX

Add and subtract with exchange and Subtract and add with exchange.

Syntax

op{cond} {Rd}, Rn, Rm

where:

•

op is one of:

UASX: Add and subtract with exchange.

USAX: Subtract and add with exchange.

•

‘cond’ is an optional condition code (see Conditional execution on page 64)

•

‘Rd’ is the destination register

•

‘Rn’ ‘Rm’ are registers holding the first and second operands

Operation

The UASX instruction:

Subtracts the top halfword of the second operand from the bottom halfword of the first

operand.

Writes the unsigned result from the subtraction to the bottom halfword of the

destination register.

Adds the top halfword of the first operand with bottom halfword of the second operand.

Writes the unsigned result of the addition to the top halfword of the destination register.

The USAX instruction:

Adds the bottom halfword of the first operand with the top halfword of the second

operand.

Writes the unsigned result of the addition to the bottom halfword of the destination

Subtracts the bottom halfword of the second operand from the top halfword of the first

operand.

Writes the unsigned result from the subtraction to the top halfword of the destination

Restrictions

Do not use SP and do not use PC.

Condition flags

These instructions do not affect the condition code flags.

Examples

UASX R0, R4, R5

; Adds top halfword of R4 to bottom halfword of R5 and

; writes to top halfword of R0

; Subtracts bottom halfword of R5 from top halfword of R0

; and writes to bottom halfword of R0

USAX R7, R3, R2

; Subtracts top halfword of R2 from bottom halfword of R3

; and writes to bottom halfword of R7

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