Freescale Semiconductor SC140 Static Programming Rules, Hardware Loops, Hardware Loop Detection

Static Programming Rules

7.4.10 Hardware Loops

The loop count “LCn” and start address “SAn” registers are described in Section 5.4.1, “Loop Programming Model,” on page 5-25.

The VLES addresses “LA, LA-1, LA-2” (relative to the loop end (last) address) and “SA, SA-1, SA-2” (relative to the loop start address) are defined in Section 5.4.2, “Loop Notation and Encoding,” on page 5-26. The minus “-” notation adjusts the VLES address earlier in the source code order.

The term “active loop” is defined in Section 5.4.4, “Loop Nesting,” on page 5-28.

All references to “in a loop” in this manual refer to both long and short loops, unless explicitly stated.

7.4.10.1 Enabled Loop

In a nested loop structure, more than one loop can be enabled at the same time. A loop n is enabled when its LFn bit in SR is set, where n is the loop index. The assembler’s static rule detection assumes loop n is enabled from the VLES after the VLES having the DOENn/DOENSHn instruction to LA of loop n (as specified by the LOOPENDn directive).

7.4.10.2 Enveloping Loop

In a nested loop structure, a loop “B” is nested inside another loop “A”. For this pair of loops, loop “B” is called a “nested loop” and loop “A” is called an “enveloping loop”. That is, loop “A” envelopes (surrounds or contains) loop “B”. This definition is relative to each loop pair. If another loop “C” is nested inside loop “B”, loop “C” becomes the nested loop and loop “B” becomes the enveloping loop for this loop pair.

Loops “A” and “B” are required to have ordered (but not adjacent) loop indexes. The assembler’s static rule detection assumes the boundaries of loop n are from the VLES after the VLES having the DOENn/DOENSHn instruction to LA of loop n (as specified by the LOOPENDn directive).

7.5 Static Programming Rules

Static programming rules are detected by examining the mnemonic/symbolic source code within the visibility of the assembler. Generally the assembler has visibility over a single source file with its INCLUDE files and MACRO expansions. The assembler detects all static rules in sequential VLES within its visibility.

7.5.1 Hardware Loop Detection

The assembler detects static rules for hardware loop iterations (LA to SA sequences) when all loop source code including the DOENn/DOENSHn instruction, LOOPSTARTn and LOOPENDn assembler directives for all nesting levels are within its visibility. The assembler rule detection makes the following assumptions:

•The loop flags (LFn and SLF) in SR are not changed within an active loop.

•Each loop n has one SA and one LA specified by the LOOPSTARTn and LOOPENDn directives, respectively.

•Loops enter at SA and exit from LA, except for exits using loop control instructions: BREAK and

CONT/CONTD.

SC140 DSP Core Reference Manual 7-7