Freescale Semiconductor SC140 Rule Detection Across COF Boundaries, Cycle-Based COF Rules

Models: SC140

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Dynamic Programming Rules

7.6.5 Rule Detection Across COF Boundaries

Some sequencing rules may be violated across COF boundaries — between instructions that are before the COF instruction or grouped in a VLES with the COF instruction (or its delay slot), and instructions at or after the COF destination. The assembler does not analyze this control flow and lacks the run-time execution trace to detect these cases. In addition, the code segments containing the COF instruction and the COF destination may be in two independently assembled source files, thus outside the visibility of the assembler. However, the simulator can detect most rule violations across COF boundaries by examining the simulation trace.

For example, the assembler cannot detect SR.2 across a COF boundary, but the simulator can detect it from the simulation trace.

Example 7-82. SR.2 Across a COF Boundary

pop sr bra fred

...

fred

add d1,d2,d3

;not allowed by SR.2

The assembler cannot detect the A.2 violation between the delay slot and the COF destination shown below, but the simulator can detect it from the simulation trace.

Example 7-83. A.2 from a Delay Slot to a COF Destination

jmpd _dest

bmset #3,r0.l;2-cycle instruction

...

_dest

move.l (r0),d0

;not allowed by A.2

7.6.5.1 Cycle-Based COF Rules

Cycle-based COF rules calculate the COF cycle count to determine if the sequence is allowed or not. Cycle-based rule violations across COF boundaries are relatively rare because the COF instruction, taking multiple cycles, creates a “cycle barrier” between the VLES having the COF instruction and the VLES at the COF destination. However, this cycle barrier is reduced when the instructions are grouped in a VLES with the COF instruction (or its delay slot).

The relevant cycle-based rules that the simulator detects across COF boundaries are:

A.1

A.2

A.2a

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SC140 DSP Core Reference Manual

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Freescale Semiconductor SC140 specifications Rule Detection Across COF Boundaries, Cycle-Based COF Rules