Motorola 24-Bit Digital Signal Processor, DSP56000 Normalize Accumulator Iteration, Norm R3,A

INSTRUCTION DESCRIPTIONS

	NORM					Normalize Accumulator Iteration		NORM
Operation:			• U •				Assembler Syntax:
	If						NORM	Rn,D
		E			Z=1, then ASL D and Rn–1➞Rn
	else if			E=1, then ASR D and Rn+1➞Rn

else NOP

where E denotes the logical complement of E, and where • denotes the logical AND operator

Description: Perform one normalization iteration on the specified destination operand D, update the specified address register Rn based upon the results of that iteration, and store the result back in the destination accumulator. This is a 56-bit operation. If the accumulator extension is not in use, the accumulator is unnormalized, and the accumu- lator is not zero, the destination operand is arithmetically shifted one bit to the left, and the specified address register is decremented by 1. If the accumulator extension register is in use, the destination operand is arithmetically shifted one bit to the right, and the specified address register is incremented by 1. If the accumulator is normalized or zero, a NOP is executed and the specified address register is not affected. Since the operation of the NORM instruction depends on the E, U, and Z condition code register bits, these bits must correctly reflect the current state of the destination accumulator prior to execut- ing the NORM instruction. Note that the L and V bits in the condition code register will be cleared unless they have been improperly set up prior to executing the NORM instruc- tion.

Example:

:
REP #$2F	;maximum number of iterations needed
NORM R3,A	;perform 1 normalization iteration
:

A

Before Execution

$00:000000:000001

A

After Execution

$00:400000:000000

R3

$0000

R3

$FFD2

Explanation of Example: Prior to execution, the 56-bit A accumulator contains the value $00:000000:000001, and the 16-bit R3 address register contains the value $0000. The repetition of the NORM R3,A instruction normalizes the value in the 56-bit accumu- lator and stores the resulting number of shifts performed during that normalization pro-

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