Modifying Dag Registers - Analog Devices ADSP-21261 SHARC Hardware Reference Manual

There is one set of registers (
interrupt on circular buffer overflow (address wraparound).
information, see "Using DAG Status" on page 4-9.
When a program needs to use
DSP has the circular buffer overflow interrupts unmasked, the program
should disable the generation of these interrupts by setting the
/ registers to values that prevent the interrupts from occurring. If
L7 L15
were accessing the address range 0x1000 – 0x2000, the program could set
= 0x0000 and
B7
buffer interrupt based on the wraparound equations
the register to zero does not necessarily achieve the desired results. If the
L
program is using either of the circular buffer overflow interrupts, it should
avoid using the corresponding
branching is not needed.
There are two special cases to be aware of when using circular buffers.
1. In the case of circular buffer overflow interrupts, if
register
every change of
crosses the base register (
dent of the context of the DAG registers, both primary and
alternate.
2. When a LW access, SIMD access, or normal word access with the
LW option crosses the end of the circular buffer, the processor
completes the access before responding to the end of buffer
condition.

Modifying DAG Registers

The DAGs support two operations that modify an address value in an
index register without outputting an address. These two operations,
address bit-reversal and address modify, are useful for bit-reverse address-
ing and maintaining pointers.
ADSP-2126x SHARC Processor Hardware Reference
and
I7
I7
= 0xFFFF. Because the DSP generates the circular
L7
register(s) (
I
(or
L7 = 0 L15 = 0
(or
I7 I15
B7
Data Address Generators
) in each DAG that can generate an
I15
or without circular buffering and the
I15
or
I7 I15
), the (or
CB7I CB15I
) after the index register (
or ) value. This behavior is indepen-
B15
For more
/ and
B7 B15
on page 4-16, setting
) where interrupt
and
CBUFEN = 1
) interrupt occurs at
or )
I7 I15
4-17
I7