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UM10316_0
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 00.06 — 17 December 2008
532 of 571
NXP Semiconductors
UM10316
Chapter 30: LPC29xx General Purpose DMA (GPDMA) controller
7. Write the channel configuration information into the DMACCxConfig register. If the
enable bit is set then the DMA channel is automatically enabled.
6.2 Flow control
The peripheral that controls the length of the packet is known as the flow controller. The
flow controller is usually the DMA Controller where the packet length is programmed by
software before the DMA channel is enabled. If the packet length is unknown when the
DMA channel is enabled, either the source or destination peripherals can be used as the
flow controller.
For simple or low-performance peripherals that know the packet length (that is, when the
peripheral is the flow controller), a simple way to indicate that a transaction has completed
is for the peripheral to generate an interrupt and enable the processor to reprogram the
DMA channel.
The transfer size value (in the DMACCxControl register) is ignored if a peripheral is
configured as the flow controller.
When the DMA transfer is completed:
1. The DMA Controller issues an acknowledge to the peripheral in order to indicate that
the transfer has finished.
2. A TC interrupt is generated, if enabled.
3. The DMA Controller moves on to the next LLI.
The following sections describe the DMA Controller data flow sequences for the four
allowed transfer types:
•
Memory-to-peripheral.
•
Peripheral-to-memory.
•
Memory-to-memory.
•
Peripheral-to-peripheral.
Each transfer type can have either the peripheral or the DMA Controller as the flow
controller so there are eight possible control scenarios.
indicates the request signals used for each type of transfer.
Table 466. DMA request signal usage
Transfer direction
Request generator
Flow controller
Memory-to-peripheral
Peripheral
DMA Controller
Memory-to-peripheral
Peripheral
Peripheral
Peripheral-to-memory
Peripheral
DMA Controller
Peripheral-to-memory
Peripheral
Peripheral
Memory-to-memory
DMA Controller
DMA Controller
Source peripheral to destination peripheral
Source peripheral and destination peripheral
Source peripheral
Source peripheral to destination peripheral
Source peripheral and destination peripheral
Destination peripheral
Source peripheral to destination peripheral
Source peripheral and destination peripheral
DMA Controller