DSP Core Instruction Set

A.1.5.1 One-Word Low Register Prefix

Includes information on grouping, looping, and IFc (conditional execution).

Instruction Formats and Opcodes

Prefix WordsCyclesType

1W LOW

REG

0

4

PREFIX

1

Opcode

15

8

7

0

1 0 0 1 a a a 0 1 1 0 p j c c c

Instruction Fields

aaa:

Number of instruction words being grouped, including the prefix word minus one. If aaa

 

equals zero, this is a NOP instruction that is not dispatched for either a single, stand-alone

 

NOP, or an intra-set NOP [0

≤ aaa ≤ 7].

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 instructions. The numbers relate to the relative word

 

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.

 

Example:

 

 

lpmarkB

;(set LA – 2)

 

_last

;(set LA – 1)

 

;(set LA)

 

In the case of a loop with two execution sets such as SA mark, the lpmarkB bit is set in the first

 

execution set of the loop.

 

 

Example:

 

 

_start execution_setlpmarkb

j:

_last execution_set

;(this is a loop on two execution sets)

lpmarkA bit

 

 

In case of a loop with more than three execution sets, the lpmarkA bit is set in the prefix of the

execution set which is at _last only if there are any SKIPLS, BREAK, CONT, CONTD to _last, or to _last-1.

A-8

SC140 DSP Core Reference Manual

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Freescale Semiconductor SC140 specifications Instruction Formats and Opcodes, Instruction Fields, Aaa, Ccc