UM10360 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
User manual Rev. 3 — 19 December 2013 613 of 841
NXP Semiconductors
UM10360
Chapter 31: LPC176x/5x General Purpose DMA (GPDMA)
31.6.5.1 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.
31.6.5.1.1 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.
3. Write the first linked list item, previously written to memory, to the relevant channel in
the DMA Controller.
4. Write the channel configuration information to the channel Configuration Register and
set the Channel Enable bit. The DMA Controller then transfers the first and then
subsequent packets of data as each linked list item is loaded.
5. An interrupt can be generated at the end of each LLI depending on the Terminal
Count bit in the DMACCxControl Register. If this bit is set an interrupt is generated at
the end of the relevant LLI. The interrupt request must then be serviced and the
relevant bit in the DMACIntTCClear Register must be set to clear the interrupt.
31.6.5.1.2 Example of scatter/gather DMA
See Figure 135
for an example of an LLI. A section of memory is to be transferred to a
peripheral. The addresses of each LLI entry are given, in hexadecimal, at the left-hand
side of the figure. In this example, the LLIs describing the transfer are to be stored
contiguously from address 0x2002 0000, but they could be located anywhere. The right
side of the figure shows the memory containing the data to be transferred.
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