Atmel SAM4S Series, Preliminary Data Sheet

Page: 143 / 1163

143
11100B–ATARM–31-Jul-12
SAM4S Series [Preliminary]
11.6.6.7 SMMLA and SMMLS
Signed Most Significant Word Multiply Accumulate and Signed Most Significant Word Multiply
Subtract
Syntax
op{R}{cond} Rd, Rn, Rm, Ra
where:
Operation
The
SMMLA
instruction interprets the values from
Rn
and
Rm
as signed 32-bit words.
The
SMMLA
instruction:
• Multiplies the values in
Rn
and
Rm
.
• Optionally rounds the result by adding
0x80000000
.
• Extracts the most significant 32 bits of the result.
• Adds the value of
Ra
to the signed extracted value.
• Writes the result of the addition in
Rd
.
The
SMMLS
instruction interprets the values from
Rn
and
Rm
as signed 32-bit words.
The
SMMLS
instruction:
• Multiplies the values in
Rn
and
Rm
.
• Optionally rounds the result by adding
0x80000000
.
• Extracts the most significant 32 bits of the result.
• Subtracts the extracted value of the result from the value in
Ra
.
• Writes the result of the subtraction in
Rd
.
Restrictions
In these instructions:
• Do not use SP and do not use PC.
Condition Flags
These instructions do not affect the condition code flags.
op is one of:
SMMLA
Signed Most Significant Word Multiply Accumulate.
SMMLS Signed Most Significant Word Multiply Subtract.
R
is a rounding error flag. If
R
is specified, the result is rounded instead of being truncated.
In this case the constant 0x80000000 is added to the product before the high word is
extracted.
cond is an optional condition code, see “Conditional Execution” .
Rd is the destination register.
Rn, Rm are registers holding the first and second multiply operands.
Ra is the register holding the accumulate value.