Motorola 24-Bit Digital Signal Processor, DSP56000 End Current do Loop, Immediately before Enddo

INSTRUCTION DESCRIPTIONS

	ENDDO	End Current DO Loop	ENDDO
Operation:		Assembler Syntax:
SSL(LF) ➞ SR;SP – 1➞ SP		ENDDO

SSH ➞ LA; SSL ➞ LC;SP –1 ➞ SP

Description: Terminate the current hardware DO loop before the current loop counter (LC) equals one. If the value of the current DO loop counter (LC) is needed, it must be read before the execution of the ENDDO instruction. Initially, the loop flag (LF) is restored from the system stack and the remaining portion of the status register (SR) and the program counter (PC) are purged from the system stack. The loop address (LA) and the loop counter (LC) registers are then restored from the system stack.

Restrictions: Due to pipelining and the fact that the ENDDO instruction accesses the program controller registers, the ENDDO instruction must not be immediately preceded by any of the following instructions:

Immediately before ENDDO	MOVEC to LA, LC, SR, SSH, SSL, or SP
	MOVEM to LA, LC, SR, SSH, SSL, or SP
	MOVEP to LA, LC, SR, SSH, SSL, or SP
	MOVEC from SSH
	MOVEM from SSH
	MOVEP from SSH
	ORI MR
	ANDI MR
	REP

Also, the ENDDO instruction cannot be the last (LA) instruction in a DO loop.

Example:
:
DO Y0,NEXT	;exec. loop ending at NEXT (Y0) times
:
MOVEC LC,A	;get current value of loop counter (LC)
CMP Y1,A	;compare loop counter with value in Y1
JNE ONWARD	;go to ONWARD if LC not equal to Y1
ENDDO	;LC equal to Y1, restore all DO registers
JMP NEXT	;go to NEXT
ONWARD :	;LC not equal to Y1, continue DO loop
:	;(last instruction in DO loop)
NEXT MOVE #$123456,X1	;(first instruction AFTER DO loop)

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