Datasheet

154
SAM4S Series [DATASHEET]
11100F–ATARM–29-Jan-14
12.6.7.1 SSAT and USAT
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 “Conditional Execution” .
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.
LSL #s 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
n
-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.