Freescale-semiconductor StarCore SC140 Manual do Utilizador Página 262

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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 on page A-18
INSERT or EXTRACT/U instructions
Integer double precision instructions such as IMACxx, IMACxxxx, IMPYxx, IMPYxxxx and
IMPY.W
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