Skip to main content

What Is Direct Memory Access (DMA)?

 

Direct Memory Access (DMA) is a feature of computer systems that allows hardware subsystems to access main system memory (RAM) with minimal intervention from the Central Processing Unit (CPU).

The Direct Memory Access (DMA) hardware peripheral on PIC® microcontrollers (MCUs) allows for direct memory-to-memory and peripheral-to-memory transfers and concurrent operation of the DMA and the CPU (while sharing system bus resources). This enables more flexible usage of eXtreme Low Power (XLP) technologies through core-independent movement of data in low-power modes and improvements in data throughput and latency.

 


 

Why Is DMA Used?

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

How Is DMA Used?

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).

 

Labels:

Comments

Post a Comment

Popular posts from this blog

How to Play a Sound After a Terminal Command Completes

  Sometimes, while working on the terminal, especially during long-running processes, it’s useful to have an audible notification when the task is finished. In this guide, we’ll show you how to make your terminal play a sound after any command completes, ensuring you're alerted without constantly checking the terminal. Why Do This? This trick can save time and improve workflow, especially when: You’re running lengthy build processes or installations. You’re waiting for large file transfers. You're programming embedded systems and need confirmation when flashing is done. Let’s dive into how to do this on a Linux system. Step-by-Step Guide to Playing a Sound After a Command 1. Using paplay or aplay to Play Sounds On most Linux distributions, you can use paplay or aplay to play sound files directly from the terminal. Here's how you can append a sound notification after a command. Basic Command Structure : PC:~$ your_command && paplay /path/to/soundfile.oga  Or, if...
Post a Comment
Read more

Building a Robot Actuator with ESP32 and a 5010 BLDC Motor

Introduction Modern robotics demands actuators that aren’t just strong, but also smart — capable of precise control, smooth motion, and safe human interaction. Traditional servos are great for small robots, but they can be stiff, noisy, and limited in range or torque. This project demonstrates a custom robot actuator built around a 5010 360 KV brushless DC (BLDC) motor , controlled by an ESP32 running the SimpleFOC library. The goal is to create a compliant joint — one that can be moved by hand, but automatically returns to its home position with adaptive stiffness. 🧠 What Makes This Actuator Special Unlike a typical servo, this actuator behaves intelligently : You can turn it by hand — it feels soft and back-drivable. When you release it, the motor returns to its initial position smoothly. If you twist it harder (e.g., due to gear reduction), it becomes stiffer , resisting displacement more strongly. It’s powered by 12 V and controlled by a simple ESP32 boar...
Post a Comment
Read more

Heating with Electric Radiators

You want to heat your small garage using a couple of electric radiators. The power and voltage requirements for each radiator are 1200 W, 240 V. But you are not sure how to wire the radiators to the power supplied to the garage. Should you use the wiring diagram on the left or the one on the right? Does it make any difference?
Post a Comment
Read more