A.1.5.2 two-word prefix, A.1.5.2, Instruction formats and opcodes – Freescale Semiconductor StarCore SC140 User Manual
Page 323: Instruction fields
DSP Core Instruction Set
SC140 DSP Core Reference Manual
A-9
Example:
skipl _last ;(there is a skipl to _last in the program)
.
.
.
execution_set
execution_set
_last execution_setlpmarkA
In the case of the loop having just one execution, the lpmarkA bit is set in the prefix of this
single execution set of the loop.
A.1.5.2 Two-Word Prefix
Includes information on grouping, looping, IFc (conditional execution), and high-register banks (D8-D15,
R8-R15).
Instruction Formats and Opcodes
Note:
The order of the register bank encoding fields is, for example, E1 E2 E3, with E1 occupying the most significant bit
position in the table.
Instruction Fields
aaa:
Number of instruction words being grouped, including the prefix word minus one (for
example, 2-w prefix + 2 grouped instruction words, aaa = 3).
For a 2-w prefix at the beginning of the execution set, aaa = 000 and aaa = 001 are reserved as
escape codes to signify that more prefix words are concatenated to support architectures with 3
or more prefix words. Use of a 2-w prefix in the middle of the set is reserved for future
encoding (such as accelerator or predication instructions) and should not be placed as a NOP.
ccc:
Conditional execution of the entire execution set.
In the following table, true/false relates to the state of the T bit in SR. D0, D1, D2, and D3 are
DALU instructions, A0 and A1 are AGU or BMU instructions. The numbers relate to the
relative offset of the instruction from the beginning of the set.
000—Unconditionally executed
001—If true (D0, D2, A0), if false (D1, D3, A1)
010—If true, all the set
011—If false, all the set
100—Reserved
101—Reserved
110—If true (D0, D2, A0), always (D1, D3, A1)
111—If false (D0, D2, A0), always (D1, D3, A1)
p:
lpmarkB bit
In the case of a loop with three or more execution sets, the lpmarkB bit is a one in the
execution set that is two before the last execution set in the loop.
Prefix
Words Cycles Type
Opcode
15
8
7
0
2W PREFIX
2
0
4
0
0
1
1
a
a
a
0
H
t
h
p
j
c
c
c
1
0
1
b
B
e
E
T
b
B
e
E
b
B
e
E