Freescale Semiconductor StarCore SC140 - Manual (Page 294)

7-44 SC140 DSP Core Reference Manual
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