
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
582 of 808
NXP Semiconductors
UM10360
Chapter 31: LPC17xx General Purpose DMA (GPDMA) controller
6.2 Flow control
The device that controls the length of the packet is known as the flow controller. On the
LPC17xx, the flow controller is always the DMA Controller, and the packet length is
programmed by software before the DMA channel is enabled.
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.
indicates the request signals used for each type of transfer.
6.2.1 Peripheral-to-memory or memory-to-peripheral DMA flow
For a peripheral-to-memory or memory-to-peripheral DMA flow, the following sequence
occurs:
1. Program and enable the DMA channel.
2. Wait for a DMA request.
3. The DMA Controller starts transferring data when:
–
The DMA request goes active.
–
The DMA stream has the highest pending priority.
–
The DMA Controller is the bus master of the AHB bus.
4. If an error occurs while transferring the data, an error interrupt is generated and
disables the DMA stream, and the flow sequence ends.
5. Decrement the transfer count.
6. If the transfer has completed (indicated by the transfer count reaching 0):
–
The DMA Controller responds with a DMA acknowledge.
–
The terminal count interrupt is generated (this interrupt can be masked).
Table 548. DMA request signal usage
Transfer direction
Request generator
Flow controller
Memory-to-peripheral
Peripheral
DMA Controller
Peripheral-to-memory
Peripheral
DMA Controller
Memory-to-memory
DMA Controller
DMA Controller
Source peripheral to destination peripheral
Source peripheral and destination peripheral
DMA Controller