7-10
ADSP-2126x SHARC Processor Hardware Reference
Once a program starts a DMA process, the process is influenced by two
external controls—DMA channel priority and DMA chaining. For more
information, see
“Managing DMA Channel Priority” on page 7-18
or
Chaining DMA Processes
The location of the DMA parameters for the next sequence comes from
the chain pointer (
CP
) register. In chained DMA operations, the
ADSP-2126x processor automatically initializes and then begins another
DMA transfer when the current DMA transfer is complete. In addition to
the standard DMA parameter registers, each DMA channel (SP and SPI)
also has a
CP
register that points to the next set of DMA parameters stored
in the processor’s internal memory. In the SPI this is the
CPSPI
and in the
SPORT it is
CPSPxy
. Each new set of parameters is stored in a four-word,
user initialized buffer in internal memory known as a transfer control
block (TCB). In TCB chain loading, the ADSP-2126x’s IOP automati-
cally reads the TCB from internal memory and then loads the values into
the channel parameter registers to set up the next DMA sequence.
The structure of a TCB is conceptually the same as that of a traditional
linked-list. Each TCB has several data values and a pointer to the next
TCB. Further, the chain pointer of a TCB may point to itself to con-
stantly reiterate the same DMA.
A DMA sequence is defined as the sum of the DMA transfers for a single
channel, from when the parameter registers initialize to when the count
register decrements to zero. Each DMA channel has a chaining enable bit
(
CHEN
) in the corresponding control register. This bit must be set to one to
enable chaining. Chain pointer register should be cleared first before
enabling chaining. When chaining is enabled, DMA transfers are initiated
by writing a memory address to the
CP
register. This is also an easy way to
start a single DMA sequence, with no subsequent chained DMAs.
The
CP
register can be loaded at any time during the DMA sequence. This
allows a DMA channel to have chaining disabled (
CP
register address
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 ...