Atmel SAM4S Series, Preliminary Data Sheet

Page: 123 / 1163

123
11100B–ATARM–31-Jul-12
SAM4S Series [Preliminary]
11.6.5.14 SASX and SSAX
Signed Add and Subtract with Exchange and Signed Subtract and Add with Exchange.
Syntax
op{cond} {Rd}, Rm, Rn
where:
Operation
The
SASX
instruction:
1. Adds the signed top halfword of the first operand with the signed bottom halfword of the
second operand.
2. Writes the signed result of the addition to the top halfword of the destination register.
3. Subtracts the signed bottom halfword of the second operand from the top signed high-
word of the first operand.
4. Writes the signed result of the subtraction to the bottom halfword of the destination
register.
The
SSAX
instruction:
1. Subtracts the signed bottom halfword of the second operand from the top signed high-
word of the first operand.
2. Writes the signed result of the addition to the bottom halfword of the destination
register.
3. Adds the signed top halfword of the first operand with the signed bottom halfword of the
second operand.
4. Writes the signed result of 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
SASX 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
; R4 and writes to bottom halfword of R0
SSAX 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 with bottom halfword of R2 and
; writes to top halfword of R7.
op is any of:
SASX Signed Add and Subtract with Exchange.
SSAX
Signed Subtract and Add with Exchange.
cond is an optional condition code, see “Conditional Execution” .
Rd is the destination register.
Rn, Rm are registers holding the first and second operands.