Vles extension words exceed two -12, Two-word instructions exceed two -12, Rule g.p.1 – Freescale Semiconductor StarCore SC140 User Manual
Page 262
7-12
SC140 DSP Core Reference Manual
Static Programming Rules
Rule G.P.1
Up to two extension words can be grouped in a VLES. This means:
•
A three-word instruction can only be grouped in a VLES with one-word instructions.
Example 7-16 VLES Extension Words Exceed Two
[
bmset #$ab34,d3.l
; 1
st
extension word
move.l #$f0d0,vba
; not allowed - 2
nd
& 3
rd
extension word
]
•
A two-word instruction can only be grouped in a VLES with one other two-word instruction and/or
one-word instructions.
Example 7-17 Two-Word Instructions Exceed Two
[
move.f #$1234,d0
; 1
st
extension word
extract #8,#16,d0,d2
; 2
nd
extension word
extractu #8,#24,d0,d3
; not allowed - 3
rd
extension word
zxt.b d0,d0
]
The second and third words of an instruction are called “extension words.” An extension word can occur in
the following cases:
•
Some immediate values
•
Some absolute addresses or offsets
•
Bit mask instructions listed in
Table A-16: Prefix Instructions
•
INSERT or EXTRACT/U instructions
•
Integer double precision instructions such as IMACxx, IMACxxxx, IMPYxx, IMPYxxxx and
IMPY.W