User manual

...the world's most energy friendly microcontrollers
2012-04-24 - Giant Gecko Family - d0053_Rev0.96 49
www.energymicro.com
8 DMA - DMA Controller
0
1 2 3 4
DMA
controller
Flash
RAM
External Bus
Interface
Peripherals
Quick Facts
What?
The DMA controller can move data without
CPU intervention, effectively reducing the
energy consumption for a data transfer.
Why?
The DMA can perform data transfers more
energy efficiently than the CPU and allows
autonomous operation in low energy modes.
The LEUART can for instance provide full
UART communication in EM2, consuming
only a few µA by using the DMA to move data
between the LEUART and RAM.
How?
The DMA controller has multiple highly
configurable, prioritized DMA channels.
Advanced transfer modes such as ping-pong
and scatter-gather make it possible to tailor
the controller to the specific needs of an
application.
8.1 Introduction
The Direct Memory Access (DMA) controller performs memory operations independently of the CPU.
This has the benefit of reducing the energy consumption and the workload of the CPU, and enables
the system to stay in low energy modes when moving for instance data from the USART to the RAM,
or from the External Bus Interface to the DAC. The DMA controller uses the PL230 µDMA controller
licensed from ARM
1
. Each of the PL230s channels can on the EFM32 be connected to any of the EFM32
peripherals.
8.2 Features
• The DMA controller is accessible as a memory mapped peripheral
• Possible data transfers include
• RAM/External Bus Interface/Flash to peripheral
• Peripheral to RAM/External Bus Interface
• RAM/External Bus Interface/Flash to RAM/External Bus Interface
• The DMA controller has 12 independent channels
• Each channel has one (primary) or two (primary and alternate) descriptors
• The configuration for each channel includes
• Transfer mode
• Priority
• Word-count
• Word-size (8, 16, 32 bit)
• The transfer modes include
• Basic (using the primary or alternate DMA descriptor)
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ARM PL230 homepage [http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0417a/index.html]