
DR
AFT
DR
AFT
DRAFT
DR
D
RAFT
DRAFT
DRA
FT DRAF
D
RAFT DRAFT DRAFT DRAFT DRAFT D
DRAFT
D
RAFT DRA
FT DRAFT DRAFT DRAFT DRA
UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
585 of 808
NXP Semiconductors
UM10360
Chapter 31: LPC17xx General Purpose DMA (GPDMA) controller
6.4.1 Word-aligned transfers across a boundary
The channel is configured for 16-transfer bursts, each transfer 32-bits wide, to a
destination for which address incrementing is enabled. The start address for the current
burst is 0x0C000024, the next boundary (calculated from the burst size and transfer
width) is 0x0C000040.
The transfer will be split into two AHB transactions:
•
a 7-transfer burst starting at address 0x0C000024
•
a 9-transfer burst starting at address 0x0C000040.
6.5 Scatter/gather
Scatter/gather is supported through the use of linked lists. This means that the source and
destination areas do not have to occupy contiguous areas in memory. Where
scatter/gather is not required, the DMACCxLLI Register must be set to 0.
The source and destination data areas are defined by a series of linked lists. Each Linked
List Item (LLI) controls the transfer of one block of data, and then optionally loads another
LLI to continue the DMA operation, or stops the DMA stream. The first LLI is programmed
into the DMA Controller.
The data to be transferred described by a LLI (referred to as the packet of data) usually
requires one or more DMA bursts (to each of the source and destination).
6.5.1 Linked list items
A Linked List Item (LLI) consists of four words. These words are organized in the following
order:
1. DMACCxSrcAddr.
2. DMACCxDestAddr.
3. DMACCxLLI.
4. DMACCxControl.
Note:
The DMACCxConfig DMA channel Configuration Register is not part of the linked
list item.
6.5.1.1
Programming the DMA controller for scatter/gather DMA
To program the DMA Controller for scatter/gather DMA:
1. Write the LLIs for the complete DMA transfer to memory. Each linked list item contains
four words:
–
Source address.
–
Destination address.
–
Pointer to next LLI.
–
Control word.
The last LLI has its linked list word pointer set to 0.
2. Choose a free DMA channel with the priority required. DMA channel 0 has the highest
priority and DMA channel 7 the lowest priority.