D950-CORE datasheet(18/89 Pages) STMICROELECTRONICS

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D950-Core

The ALU output is always made to one of the two accumulators and the CCR (with the

exception of particular ALU codes which affect only CCR or an accumulator). The ALU

operations can be partitioned into three different groups (see Section 5.4.2), depending on the

number of operands the operation requires:

Specific ALU codes (see Section 5.4.2) are used to implement a non-restoring conditional

add/subtract division algorithm. The division can be signed or unsigned. The dividend must be

a 32-bit operand sign extended to 40-bit and located in the 40-bit accumulator. The divisor

must be a 16-bit operand located in R0 or R1 (LR-bit of STA register must be low).

In order to obtain a valid result, the absolute value of the dividend must be strictly smaller than

the absolute value of the divisor (considering operand is in a fractional format).

Special features are implemented in the D950-Core to process multi-precision data (see

DMULT instruction for double-precision MAC operations).

Two overflow preventions exist in the D950-Core (see SAT and ES bits of STA register):

1: For the multiplier, when multiplying 0x8000 by 0x8000 in signed/signed fraction-

al mode, the saturation block forces the multiplier result to 0x7FFFFFFF,

2: For the ALU, when the result overflows. Provided one of the two optional satu-

ration modes (32-bit saturation or 40-bit saturation) has been selected, the ac-

cumulator destination is set to plus or minus the maximum value.

Two rounding operations are enabled in the D950-Core (see RND-bit of STA register):

1: The multiplier result stored in P register explicitly defined by the instruction. A

two’s complement rounding is performed on the result which is stored in the 16-

bit PH register (see Section 5.4.2).

2: The 40-bit accumulator (either two’s complement or convergent rounding) pro-

vided by ALU operation (see RND-bit of STA register).

4.1.6 Bit Manipulation Unit (BMU)

The BMU allows bit manipulation operations on 16-bit data sources, accessed in 3 different

modes: direct, indirect and register addressing, through dedicated instructions.

An 8-bit mask is applied to enable the following operations on a bit-per-bit basis:

•

TSTL: bit test low.

•

TSTH: bit test high.

•

TSTHSET: bit test high and set.

•

TSTLCLR: bit test low and reset.

ALU Code

Number of Sources

Number of Destinations

3 operands

2 operands

1 operand

1 (source=destination)

D950-CORE 数据表(PDF) 18 Page - STMicroelectronics

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