Freescale Semiconductor SC140 Status and Conditions that Affect Lpmark Execution, LFn

LPMARKx

LPMARKB

For long loops (SLF=0), this prefix bit is placed at LA-2 (two sets before the last set of the loop). It instructs the active loop to decrement LCn and issue a jump delayed operation (with 2 delay slots) to SAn, if LCn is greater than one. If LCn is less than or equal to one, then the LCn register and the LFn bit are cleared. For short loops (SLF=1) of two execution sets, this prefix bit is placed at the first set of the loop (SA).

LPMARKA

For long loops (SLF=0), this prefix bit is placed at LA (the last set of the loop) and is used in special cases. It instructs the active loop machine to decrement LCn and jump to SAn if LCn is greater than one. If LCn is less than or equal to one, then the LCn register and the LFn bit are cleared. This prefix bit is used only in cases where there is a possibility that the loop machine might not be able to identify LPMARKB, which is normally used in long loops. An example is the case of nested loops where the inner loop may be skipped with SKIPLS directly to the LA of the enveloping loop. In case of short loops (SLF=1) of one execution set, LPMARKA is always placed at the first set of the loop (SA).

Table A-17. Combinations of LPMARKx Use

LPMARKA	LPMARKB	LFn	SLF	LCn	Description
no	LPMARKB	set	clear	> 1	LCn decrements by one and a jump with two delay slots
					to SAn occurs. LPMARKs appearing in the delay slots
					are ignored.
				≤ 1	LCn and LFn are cleared. The active loop is terminated.
					Every LPMARKA that appears in the next two delay slots
					is ignored.
LPMARKA	no	set	clear	> 1	LCn decrements by one and a jump to SAn occurs.
				≤ 1	LCn, LFn, and SLF are cleared. The active loop is termi-
					nated.
no	LPMARKB	set	set	> 1	LCn decrements by one and LPMARKs appearing in the
					next execution set are ignored. A jump with one delay
					slot to SAn occurs.
				≤ 1	LCn, LFn, and SLF are cleared. The active loop is termi-
					nated. LPMARKs appearing in the next execution set are
					treated.
LPMARKA	no	set	set	> 1	LCn decrements by one and a jump to SAn occurs.
				≤ 1	LCn, LFn, and SLF are cleared. The active loop is termi-
					nated.
LPMARKA	LPMARKB	set	clear	> 1	If LPMARKA and LPMARKB appear together,
					LPMARKA belongs to the inner loop and LPMARKB
LPMARKA	LPMARKB	set	set	> 1
					belongs to the outer loop.
					If the inner LCn > 1, the LPMARKB is ignored and the
					LPMARKA is executed.
					If the inner LCn ≤ 1, the inner LCn and the inner LFn are
					cleared. The active inner loop is terminated and the
					LPMARKB is executed.

Status and Conditions that Affect LPMARK Execution

The loop flag (LFn), short loop flag (SLFn), and loop counters (LCn) affect the response as described in the description above.

A-222 SC140 DSP Core Reference Manual