ADSP-2126x SHARC Processor Hardware Reference
3-13
Program Sequencer
Delayed Branches
The instruction pipeline influences how the sequencer handles delayed
branches. For immediate branches in which
JUMP
and
CALL
/
RETURN
instructions are not specified as delayed branches
(DB)
, two instruction
cycles are lost (
NOP
) as the pipeline empties and refills with instructions
from the new branch.
As shown in
, the DSP aborts the two instructions
after the branch, which are in the fetch and decode stages. For a
CALL
, the
decode address (the address of the instruction after the
CALL
) is the return
address. During the two lost
NOP
cycles, the pipeline fetches and decodes
the first instruction at the branch address.
In the illustrations that follow, shading indicates aborted instructions,
which are followed by
NOP
instructions.
Table 3-2. Pipelined Execution Cycles for Immediate Branch
(Jump/Call)
Cycles
1
2
3
4
Execute
N
NOP
NOP
J
2
Decode
N + 1–>NOP
1
N + 2–>NOP
3
J
2
J + 1
Fetch
N + 2
J
2
J + 1
J + 2
1. N + 1 suppressed
2. For call, N + 1 pushed onto PC stack
3. N + 2 suppressed
Table 3-3. Pipelined Execution Cycles for Immediate Branch (Return)
Cycles
1
2
3
4
Execute
N
NOP
NOP
R
Decode
N + 1–>NOP
1
N + 2–>NOP
3
R
R + 1
Fetch
N + 2
R
2
R + 1
R + 2
1. N + 1 suppressed
2. R (N + 1 in Figure 2-14 on page...)popped from PC stack
3. N + 2 suppressed
Summary of Contents for ADSP-21261 SHARC
Page 30: ...Contents xxx ADSP 2126x SHARC Processor Hardware Reference ...
Page 40: ...Register Diagram Conventions xl ADSP 2126x SHARC Processor Hardware Reference ...
Page 58: ...Differences From Previous SHARCs 1 18 ADSP 2126x SHARC Processor Hardware Reference ...
Page 112: ...Secondary Processing Element PEy 2 54 ADSP 2126x SHARC Processor Hardware Reference ...
Page 178: ...Summary 3 66 ADSP 2126x SHARC Processor Hardware Reference ...
Page 204: ...DAG Instruction Summary 4 26 ADSP 2126x SHARC Processor Hardware Reference ...
Page 322: ...Setting Up DMA 7 32 ADSP 2126x SHARC Processor Hardware Reference ...
Page 436: ...SPORT Programming Examples 9 86 ADSP 2126x SHARC Processor Hardware Reference ...
Page 521: ...ADSP 2126x SHARC Processor Hardware Reference 11 31 Input Data Port rts IDP_ISR end ...
Page 522: ...Input Data Port Programming Example 11 32 ADSP 2126x SHARC Processor Hardware Reference ...
Page 590: ...Timer Programming Examples 14 20 ADSP 2126x SHARC Processor Hardware Reference ...
Page 796: ...I O Processor Registers A 174 ADSP 2126x SHARC Processor Hardware Reference ...
Page 800: ...B 4 ADSP 2126x SHARC Processor Core Manual ...
Page 846: ...Index I 36 ADSP 2126x SHARC Processor Hardware Reference ...