Analog Devices ADSP-21261 SHARC Hardware Reference Manual page 191

updating the index on each access with a positive or negative modify value
( register or immediate value). If the index pointer falls outside the buf-
M
fer, the DAG subtracts from or adds to the length of the buffer value,
wrapping the index pointer back to the start of the buffer. The DAG's
support for circular buffer addressing appears in
and an example of circular buffer addressing appears in
The starting address that the DAG wraps around is called the buffer's base
address ( register). There are no restrictions on the value of the base
B
address for a circular buffer.

Circular buffering may only use post-modify addressing. The
DAG's architecture, as shown in
support pre-modify addressing for circular buffering because circu-
lar buffering requires that the index be updated on each access.
It is important to note that the DAGs do not detect memory map over-
flow or underflow. If the address post-modify produces
FFFF or
I – M
length of a circular buffer should not let the buffer straddle the top of the
memory map. For more information on the DSP's memory map, see
Figure 4-1 on page
As shown in Figure
lar buffer:
1. Enable circular buffering (
is only needed once in a program.
2. Load the buffer's base address into the
automatically loads the corresponding
ADSP-2126x SHARC Processor Hardware Reference
< 0, circular buffering may not function correctly. Also, the
4-3.
4-4, programs use the following steps to set up a circu-
Data Address Generators
Figure 4-1 on page
Figure 4-1 on page
BIT SET Mode1 CBUFEN;
register. This operation
B
register.
I
4-3,
Figure 4-4.
4-3, cannot
> 0xFFFF
I + M
). This operation
4-13