Atmel Xplained Pro Evaluation Kit ATSAM4E-XPRO ATSAM4E-XPRO データシート
製品コード
ATSAM4E-XPRO
SAM4E [DATASHEET]
Atmel-11157D-ATARM-SAM4E16-SAM4E8-Datasheet_12-Jun-14
472
26.5.4 DMAC Transfer Types
A DMAC transfer may consist of single or multi-buffer transfers. On successive buffers of a multi-buffer transfer,
the DMAC_SADDRx/DMAC_DADDRx registers in the DMAC are reprogrammed using either of the following
methods:
the DMAC_SADDRx/DMAC_DADDRx registers in the DMAC are reprogrammed using either of the following
methods:
Buffer chaining using linked lists
Contiguous address between buffers
On successive buffers of a multi-buffer transfer, the DMAC_CTRLAx and DMAC_CTRLBx registers in the DMAC
are re-programmed using either of the following methods:
are re-programmed using either of the following methods:
Buffer chaining using linked lists
When buffer chaining using linked lists is the multi-buffer method of choice, and on successive buffers, the
DMAC_DSCRx register in the DMAC is re-programmed using the following method:
DMAC_DSCRx register in the DMAC is re-programmed using the following method:
Buffer chaining using linked lists
A buffer descriptor (LLI) consists of following registers, DMAC_SADDRx, DMAC_DADDRx, DMAC_DSCRx,
DMAC_CTRLAx, DMAC_CTRLBx.These registers, along with the DMAC_CFGx register, are used by the DMAC
to set up and describe the buffer transfer.
DMAC_CTRLAx, DMAC_CTRLBx.These registers, along with the DMAC_CFGx register, are used by the DMAC
to set up and describe the buffer transfer.
26.5.4.1 Multi-buffer Transfers
Buffer Chaining Using Linked Lists
In this case, the DMAC re-programs the channel registers prior to the start of each buffer by fetching the buffer
descriptor for that buffer from system memory. This is known as an LLI update.
descriptor for that buffer from system memory. This is known as an LLI update.
DMAC buffer chaining is supported by using a Descriptor Pointer register (DMAC_DSCRx) that stores the address
in memory of the next buffer descriptor. Each buffer descriptor contains the corresponding buffer descriptor
(DMAC_SADDRx, DMAC_DADDRx, DMAC_DSCRx, DMAC_CTRLAx DMAC_CTRLBx).
in memory of the next buffer descriptor. Each buffer descriptor contains the corresponding buffer descriptor
(DMAC_SADDRx, DMAC_DADDRx, DMAC_DSCRx, DMAC_CTRLAx DMAC_CTRLBx).
To set up buffer chaining, a sequence of linked lists must be programmed in memory.
The DMAC_SADDRx, DMAC_DADDRx, DMAC_DSCRx, DMAC_CTRLAx and DMAC_CTRLBx registers are
fetched from system memory on an LLI update. The updated content of the DMAC_CTRLAx register is written
back to memory on buffer completion.
fetched from system memory on an LLI update. The updated content of the DMAC_CTRLAx register is written
back to memory on buffer completion.
shows how to use chained linked lists in memory
to define multi-buffer transfers using buffer chaining.
The Linked List multi-buffer transfer is initiated by programming DMAC_DSCRx with DSCRx(0) (LLI(0) base
address) different from zero. Other fields and registers are ignored and overwritten when the descriptor is retrieved
from memory.
address) different from zero. Other fields and registers are ignored and overwritten when the descriptor is retrieved
from memory.
The last transfer descriptor must be written to memory with its next descriptor address set to 0.