ADSP-BF535 Blackfin Processor Hardware Reference
5-7
Data Address Generators
If the index pointer falls outside the buffer range, the DAG subtracts the
length of the buffer (L-register) from the value or adds the length of the
buffer to the value, wrapping the index pointer back to a point inside the
buffer.
The starting address that the DAG wraps around is called the buffer’s base
address (B-register). There are no restrictions on the value of the base
address for circular buffers that contains 8-bit data. Circular buffers that
contain 16- and 32-bit data must be 16-bit aligned and 32-bit aligned,
respectively. Circular buffering uses post-modify addressing.
• As seen in
Figure 5-2
, on the first post-modify access to the buffer,
the DAG outputs the I-register value on the address bus, then
modifies the address by adding the modify value:
• If the updated index value is within the buffer length, the DAG
writes the value to the I-register.
• If the updated index value exceeds the buffer length, the DAG sub-
tracts (for a positive modify value) or adds (for a negative modify
value) the L-register value before writing the updated index value
to the I-register.
In equation form, these post-modify and wraparound operations work as
follows.
• If M is positive:
• I
new
= I
old
+ M
if I
old
+ M < buffer base + length (end of buffer)
• I
new
= I
old
+ M – L
if I
old
+ M
buffer base + length (end of buffer)
Содержание ADSP-BF535 Blackfin
Страница 80: ...Development Tools 1 26 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 312: ...Working With Memory 6 86 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 332: ...System Interfaces 7 20 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 360: ...Dynamic Power Management Controller 8 28 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 446: ...Beginning and Ending an SPI Transfer 10 40 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 522: ...Timing Examples 11 76 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 562: ...IrDA Support 12 40 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 608: ...PCI I O Issues 13 46 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 672: ...References 14 64 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 810: ...SDRAM Controller SDC 18 86 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 811: ...ADSP BF535 Blackfin Processor Hardware Reference 18 87 External Bus Interface Unit...
Страница 812: ...SDRAM Controller SDC 18 88 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 860: ...DMA Bus Debug Registers 20 30 ADSP BF535 Blackfin Processor Hardware Reference...
Страница 908: ...SDRAM Controller External Bus Interface Unit B 36 ADSP BF535 Blackfin Processor Hardware Reference...