Addressing With Dags - Analog Devices ADSP-21261 SHARC Hardware Reference Manual

DAG Operations
• "Addressing With DAGs" on page 4-10
• "Data Addressing Stalls" on page 4-12
• "Addressing Circular Buffers" on page 4-12
• "Modifying DAG Registers" on page 4-17
An important item to note from
adjusts the output address per the word size of the address location (short
word, normal word, or long word). This address adjustment lets internal
memory use the address directly.

SISD/SIMD mode, access word size, and data location (inter-
nal/external) all influence data access operations.

Addressing With DAGs

The DAGs support two types of modified addressing which is defined as
generating an address that is incremented by a value or a register. In
pre-modify addressing, the DAG adds an offset (modifier), which is either
an register or an immediate value, to an
M
ing address. Pre-modify addressing does not change or update the
register. The other type of modified addressing is post-modify addressing.
In post-modify addressing, the DAG outputs the
unchanged, then adds an
register value.
The difference between pre-modify and post-modify instructions in the
DSP's assembly syntax is the position of the index and modifier in the
instruction. If the
post-modify operation. If the modifier comes before the
instruction is a pre-modify without update operation. The following
instruction accesses the program memory location indicated by the value
in and writes the value
I15
R6 = PM(I15,M12); /* Post-modify addressing with update */
4-10
Figure 4-1
register or immediate value, updating the
M
Figure 4-3 compares pre- and post-modify addressing.
register comes before the modifier, the instruction is a
I
+
I15
ADSP-2126x SHARC Processor Hardware Reference
is that the DAG automatically
register and outputs the result-
I
register value
I
to the register:
M12 I15
I
I
register, the
I