DAG Operations
4-14
ADSP-2126x SHARC Processor Hardware Reference
3. Load the buffer’s length into the corresponding
L
register. For
example,
L0
corresponds to
B0
.
4. Load the modify value (step size) into an
M
register in the corre-
sponding DAG. For example,
M0
through
M7
correspond to
B0
.
Alternatively, the program can use an immediate value for the
modifier.
After circular buffering is set up, the DAGs use the modulus logic in
to process circular buffer addressing.
Using circular buffering with odd length in SIMD mode allows the
implicit move to exceed the circular buffer limits.
On the ADSP-2126x, programs enable circular buffering by setting the
CBUFEN
bit in the
MODE1
register. This bit has a corresponding mask bit in
the
MMASK
register. Setting the corresponding
MMASK
bit causes the
CBUFEN
bit to be cleared following a push status instruction (
PUSH STS
) or the exe-
cution of an external interrupt or timer interrupt. This feature allows
programs to disable circular buffering while in an interrupt service routine
that does not use circular buffering. By disabling circular buffering, the
routine does not need to save and restore the DAG’s
B
and
L
registers.
Clearing the
CBUFEN
bit disables circular buffering for all data load and
store operations. The DAGs perform normal post-modify load and store
accesses, ignoring the
B
and
L
register values. Note that a write to a
B
regis-
ter modifies the corresponding
I
register, independent of the state of the
CBUFEN
bit. The
MODIFY
instruction executes independent of the state of
the
CBUFEN
bit. The
MODIFY
instruction always performs circular buffer
modify of the index registers if the corresponding
B
and
L
registers are
configured, independent of the state of the
CBUFEN
bit.
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 ...