Multiply Accumulator (Multiplier)
2-26
ADSP-2126x SHARC Processor Hardware Reference
In addition to multiplication, fixed-point operations include accumula-
tion, rounding, and saturation of fixed-point data. There are three
MRF
register operations: clear (
Clr
), round (
Rnd
), and saturate (
Sat
).
The
Clr
operation (
MRF
=0) resets the specified
MRF
register to zero. Often,
it is best to perform this operation at the start of a multiply/accumulate
operation to remove results left over from the previous operation.
The
Rnd
operation (
MRF=Rnd MRF
) applies only to fractional results, so inte-
ger results are not effected. This operation rounds the 80-bit
MRF
value to
nearest at bit 32; for example, the
MRF1
-
MRF0
boundary. Rounding of a
fixed-point result occurs either as part of a multiply or multiply/accumu-
late operation or as an explicit operation on the
MRF
register. The rounded
result in
MRF1
can be sent either to the register file or back to the same
MRF
register. To round a fractional result to zero (truncation) instead of to
nearest, a program transfers the unrounded result from
MRF1
, discarding
the lower 32 bits in
MRF0
.
The
Sat
operation (
MRF=Sat MRF
) sets
MRF
to a maximum value if the
MRF
value has overflowed. Overflow occurs when the
MRF
value is greater than
the maximum value for the data format—unsigned or twos-complement
and integer or fractional—as specified in the saturate instruction. The six
possible maximum values appear in
. The result from
MRF
satura-
tion can be sent either to the register file or back to the same
MRF
register.
Table 2-6. Fixed-Point Format Maximum Values (For
Saturation)
Maximum Number
(Hexadecimal)
MRF2
MRF1
MRF0
Two’s-complement fractional (positive)
0000
7FFF FFFF
FFFF FFFF
Two’s-complement fractional (negative)
FFFF
8000 0000
0000 0000
Two’s-complement integer (positive)
0000
0000 0000
7FFF FFFF
Two’s-complement integer (negative)
FFFF
FFFF FFFF
8000 0000
Summary of Contents for ADSP-21261 SHARC
Page 30: ...Contents xxx ADSP 2126x SHARC Processor Hardware Reference ...
Page 40: ...Register Diagram Conventions xl ADSP 2126x SHARC Processor Hardware Reference ...
Page 58: ...Differences From Previous SHARCs 1 18 ADSP 2126x SHARC Processor Hardware Reference ...
Page 112: ...Secondary Processing Element PEy 2 54 ADSP 2126x SHARC Processor Hardware Reference ...
Page 178: ...Summary 3 66 ADSP 2126x SHARC Processor Hardware Reference ...
Page 204: ...DAG Instruction Summary 4 26 ADSP 2126x SHARC Processor Hardware Reference ...
Page 322: ...Setting Up DMA 7 32 ADSP 2126x SHARC Processor Hardware Reference ...
Page 436: ...SPORT Programming Examples 9 86 ADSP 2126x SHARC Processor Hardware Reference ...
Page 521: ...ADSP 2126x SHARC Processor Hardware Reference 11 31 Input Data Port rts IDP_ISR end ...
Page 522: ...Input Data Port Programming Example 11 32 ADSP 2126x SHARC Processor Hardware Reference ...
Page 590: ...Timer Programming Examples 14 20 ADSP 2126x SHARC Processor Hardware Reference ...
Page 796: ...I O Processor Registers A 174 ADSP 2126x SHARC Processor Hardware Reference ...
Page 800: ...B 4 ADSP 2126x SHARC Processor Core Manual ...
Page 846: ...Index I 36 ADSP 2126x SHARC Processor Hardware Reference ...