Motorola DSP56305 User Manual download pdf (Page 22)

Data Operations

The Max instruction

MOTOROLA Optimizing DSP56300/DSP56600 Applications 2-7

2.3 THE MAX INSTRUCTION

MAX is a new instruction in the DSP56300 and DSP56600

instruction set that can used to enhance performance in critical data

operation loops. For example,

max a,b

compares the two accumulators, and places the bigger value in the

destination accumulator (accumulator B). The MAXM instruction

does the same thing, only it transfers the bigger absolute value to

the destination .

Like other data operations, this instruction is effectively executed in

one clock cycle. Previously such functionality was achieved in two

cycles, for example:

cmp a,b

tlt a,b

Note: This example differs from the MAX functionality only in the

status update.

The MAXM instruction can be used to find the largest number in an

array of values, in N + 10 clock cycles:

cycles

move #DATA_POINTER,r0 1

clr b x:(r0)+,a 1+3 interlock

rep #n 5

maxm a,b x:(r0)+,a N

The initialization of R0 takes 4 cycles due to an address register

interlock. The three cycle stall could be used for other useful

instructions (see Section 6.2.1 on page 6-7).

Note: The MAX and MAXM instructions can only be used with

fixed operands (A as first source, B as destination). There is

no opcode for MAX B,A.

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Motorola DSP56305 User Manual Page 22