ADSP-2126x SHARC Processor Hardware Reference
3-15
Program Sequencer
Besides being more challenging to code, delayed branches impose some
limitations that stem from the instruction pipeline architecture. Because
the delayed branch instruction and the two instructions that follow it
must execute sequentially, the instructions in the two locations that follow
a delayed branch instruction cannot be:
• Other branches (no
JUMP
,
CALL
, or
RETURN
instructions)
Normally, it is not valid to have two conditional instructions that
use the (
DB
) option follow each other. However, where the execu-
tion of those instructions is mutually exclusive, it is allowed. For
example:
if gt jump (PC, 7) (db)
if le jump (PC,11) (db)
• Any stack manipulations (no
PUSH
or
POP
instructions or writes to
the
PC
stack or
PC
stack pointer register)
• Any loops or other breaks in sequential operation (no
DO/UNTIL
or
IDLE
instructions)
Development software for the DSP should always flag these types
of instructions as code errors in the two locations after a delayed
branch instruction.
Delayed branches and the instruction pipeline also influence interrupt
processing. Because the delayed branch instruction and the two instruc-
tions that follow it always execute sequentially, the DSP does not
immediately process an interrupt that occurs in between a delayed branch
instruction and either of the two instructions that follow. Any interrupt
that occurs during these instructions is latched, but is not processed until
the branch is complete.
This may be useful when two instructions must execute atomically (with-
out interruption), such as when working with semaphores. In the
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 ...