Nxp Semiconductors UM10237 ユーザーズマニュアル

UM10237_2

© NXP B.V. 2008. All rights reserved.

To program the GPDMA 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. The LLIs must be stored in the 
memory where the GPDMA has access to (i.e. AHB1 SRAM and external memory).

2. Choose a free DMA channel with the priority required. DMA channel 0 has the highest 

priority and DMA channel 1 the lowest priority.

3. Write the first linked list item, previously written to memory, to the relevant channel in 

the GPDMA.

4. Write the channel configuration information to the channel Configuration Register and 

set the Channel Enable bit. The GPDMA 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.

 for an example of an LLI. A rectangle of memory has to be transferred 

to a peripheral. The addresses of each line of data are given, in hexadecimal, at the 
left-hand side of the figure. The LLIs describing the transfer are to be stored contiguously 
from address 0x20000.

 

The first LLI, stored at 0x20000, defines the first block of data to be transferred, which is 
the data stored between addresses 0x0A200 and 0x0AE00:

0x--200

0x–E00

0x0A---

0x0B---

0x0C---

0x0D---

0x0E---

0x0F---

0x10---

0x11---