Atmel Xplained Pro Evaluation Kit ATSAM4E-XPRO ATSAM4E-XPRO Data Sheet

155

SAM4E [DATASHEET]

Atmel-11157D-ATARM-SAM4E16-SAM4E8-Datasheet_12-Jun-14

Signed Saturate and Unsigned Saturate to any bit position, with optional shift before saturating.

Syntax

op{cond} Rd, #n, Rm {, shift #s}

where:

op

is one of:

SSAT Saturates a signed value to a signed range.

USAT Saturates a signed value to an unsigned range.

cond

is an optional condition code, see 

Rd

is the destination register.

n

specifies the bit position to saturate to:

n ranges from 1

n ranges from 0 to 31 for USAT.

to 32 for SSAT

Rm

is the register containing the value to saturate.

shift #s

is an optional shift applied to Rm before saturating. It must be one of the
following:

ASR #s

where s is in the range 1 to 31.

where s is in the range 0 to 31.

Operation

These instructions saturate to a signed or unsigned n-bit value. 

The SSAT instruction applies the specified shift, then saturates to the signed range
-2

n–1

≤ x ≤ 2

n–1

-1.

The USAT instruction applies the specified shift, then saturates to the unsigned range 0

≤ x ≤ 2

-1.

Restrictions

Do not use SP and do not use PC

Condition Flags

These instructions do not affect the condition code flags.

If saturation occurs, these instructions set the Q flag to 1.

Examples

SSAT

R7, #16, R7, LSL #4

; Logical shift left value in R7 by 4, then 

; saturate it as a signed 16-bit value and

; write it back to R7

USATNE

R0, #7, R5

; Conditionally saturate value in R5 as an 

; unsigned 7 bit value and write it to R0.