DAG Operations
4-16
ADSP-2126x SHARC Processor Hardware Reference
• If M is positive:
I
new
= I
old
+ M if I
old
+ M < buffer base (start of buffer)
I
new
= I
old
+ M – L if I
old
+ M
buffer base + length (end of buffer)
• If M is negative:
I
new
= I
old
+ M if I
old
+ M
buffer base (start of buffer)
I
new
= I
old
+ M + L if I
old
+ M < buffer base (start of buffer)
The DAGs use all four types of DAG registers for addressing circular buf-
fers. These registers operate as follows for circular buffering.
• The index (
I
) register contains the value that the DAG outputs on
the address bus.
• The modify (
M
) register contains the post-modify amount (positive
or negative) that the DAG adds to the
I
register at the end of each
memory access. The
M
register can be any
M
register in the same
DAG as the
I
register and does not have to have the same number.
The modify value can also be an immediate value instead of an
M
register. The size of the modify value, whether from an
M
register or
immediate, must be less than the length (
L
register) of the circular
buffer.
• The length (
L
) register sets the size of the circular buffer and the
address range that the DAG circulates the
I
register through. The
L
register must be positive and cannot have a value greater than
2
31
– 1. If an
L
register’s value is zero, its circular buffer operation
is disabled.
• The DAG compares the base (
B
) register, or the
B
register plus the
L
register, to the modified
I
value after each access. When the
B
regis-
ter is loaded, the corresponding
I
register is simultaneously loaded
with the same value. When
I
is loaded,
B
is not changed. Programs
can read the
B
and
I
registers independently.
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 ...