Atmel ARM-Based Evaluation Kit for SAM4S16C, 32-Bit ARM® Cortex® Microcontroller ATSAM4S-WPIR-RD ATSAM4S-WPIR-RD Data Sheet

135

SAM4S Series [DATASHEET]

Atmel-11100G-ATARM-SAM4S-Datasheet_27-May-14

Add and Subtract with Exchange and Subtract and Add with Exchange.
Syntax

op{cond} {Rd}, Rn, Rm

where:
opis one of:
UASX Add and Subtract with Exchange.
USAX Subtract and Add with Exchange.
condis an optional condition code, see 

.

Rdis the destination register.
Rn, Rmare registers holding the first and second operands.
Operation
The UASX instruction:

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

2. Writes the unsigned result from the subtraction to the bottom halfword of the destination register.
3. Adds the top halfword of the first operand with the bottom halfword of the second operand.
4. Writes the unsigned result of the addition to the top halfword of the destination register.

The USAX instruction:

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

2. Writes the unsigned result of the addition to the bottom halfword of the destination register.
3. Subtracts the bottom halfword of the second operand from the top halfword of the first operand.
4. Writes the unsigned result from the subtraction to the top halfword of the destination register.

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

; Adds top halfword of R3 to bottom halfword of R2 and 

 ; writes to top halfword of R7.

Unsigned Halving Add 16 and Unsigned Halving Add 8
Syntax

op{cond}{Rd,} Rn, Rm

where:
opis any of:
UHADD16 Unsigned Halving Add 16.