Most CPU operations in MCU-based systems involve the movement of
data. In many cases, this can significantly limit the throughput and
responsiveness of a system. For example, an interrupt can cause the CPU
to stop what it is currently doing to service
the interrupt. In low-power applications, this can significantly
increase overall power consumption.
The DMA provides a method of
offloading data movement operations from the CPU, allowing for
concurrent execution of data transfers and CPU processing in a pipelined manner.
This reduces CPU load and interrupt overhead, thereby improving system
responsiveness and power efficiency.
The DMA peripheral can move data through two methods:
- Moving data while the CPU clock is disabled (e.g. low-power modes and XLP technology, depending on device capabilities)
- Utilizing available bus cycles when the CPU is idle or waiting for an event
Configuration Context Switching
Having multiple
configurations of peripherals can greatly expand the functionality of a
device and lowers unit costs as well as overall BOM cost. However,
changing configurations can be CPU intensive as the registers and
configuration bits for peripherals need to be altered, which could bring about performance issues in some applications.
The DMA allows for more efficient context-based configuration
through a combination of software- and hardware-based triggers that permit
automated updates of peripheral registers with reduced CPU involvement.
System Automation
The DMA
peripheral can be used to automate system processes involving data
transfer. This includes interaction with state-machine-like implementations
and reconfiguration of other Core Independent Peripherals (CIPs),
providing an efficient method of using a single peripheral in a
variety of ways in response to hardware- or software-defined triggers.
Additionally,
loop-based processes can be automated through repeated or circular DMA transfers,
increasing throughput and reducing CPU intervention.
Arbitrary Waveform Generation
Many
applications require arbitrary waveform data, which can be difficult to
manage with a software-centric system. Arbitrary waveforms are
traditionally generated using Digital Signal Processing (DSP)
techniques that require significant computation and code complexity.
The DMA can be used to create
these same arbitrary waveforms by reading data sequentially from memory
in the form of a lookup table and feeding this to other peripherals such
as a Pulse-Width Modulator (PWM) or Digital-to-Analog Converter (DAC).
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