DMA controller concept in Embedded C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does DMA stand for in embedded systems?

DMA stands for Direct Memory Access. It allows hardware to transfer data directly between memory and peripherals without CPU involvement.

beginner

How does a DMA controller improve system performance?

A DMA controller frees the CPU from handling data transfers, allowing it to perform other tasks while data moves directly between memory and devices.

intermediate

Name two common types of DMA transfer modes.

1. Burst mode: transfers a block of data at once.<br>2. Cycle stealing mode: transfers data one word at a time, interleaved with CPU cycles.

intermediate

What role does the DMA controller's channel play?

Each DMA channel manages a separate data transfer, allowing multiple devices to use DMA independently.

beginner

Explain the basic steps a DMA controller follows to transfer data.

1. CPU programs DMA controller with source, destination, and size.<br>2. DMA controller takes control of the bus.<br>3. Data is transferred directly.<br>4. DMA controller signals completion to CPU.

What is the main benefit of using a DMA controller?

A It allows data transfer without CPU intervention

B It increases CPU clock speed

C It reduces memory size

D It replaces the CPU

DMA allows data to move directly between memory and peripherals, freeing the CPU.

Which of the following is NOT a DMA transfer mode?

A Interrupt mode

B Cycle stealing mode

C Burst mode

D Block transfer mode

Interrupt mode is not a DMA transfer mode; DMA uses burst, cycle stealing, and block transfer modes.

Who programs the DMA controller with transfer details?

A Memory

B CPU

C Peripheral device

D DMA controller itself

The CPU sets up the DMA controller by providing source, destination, and transfer size.

What happens after the DMA transfer completes?

A Peripheral device shuts down

B CPU resets the DMA controller

C DMA controller signals the CPU

D Memory is cleared

The DMA controller sends an interrupt or signal to notify the CPU that the transfer is done.

How does cycle stealing mode affect CPU operation?

A CPU runs faster during DMA transfer

B DMA takes full control of the bus, stopping CPU

C DMA disables CPU interrupts

D DMA transfers one word at a time, sharing bus with CPU

Cycle stealing mode transfers data one word at a time, interleaving with CPU bus cycles.

Describe how a DMA controller works and why it is useful in embedded systems.

Think about how data moves without CPU doing all the work.

List and explain the main steps involved when a DMA controller performs a data transfer.

Focus on the sequence from setup to finish.