Introduction to Direct Memory Access (DMA)

We've learned how interrupts relieve the CPU of the burden of polling, but what about the data transfer? A DMA will handle that for us. This lesson shows how.
Takeaways: At the completion of this lesson, each student should be able to:
• explain the benefits of direct memory access (DMA),
• describe the process of cycle stealing,
• explain how a cache supports the use of DMA,
• list the four things the DMA needs to complete a transfer, and
• show how different DMA configurations affect the number of memory cycles stolen per data element transfer.
#dma #io #bus

[@Harko33]

Just discovered this channel. Awesome. You're a very good teacher, thank you.

[@toms_lii2065]

So underrated content. Thank you!

[@thuantta]

Very cool overview about what DMA is! Easy to understand explanation

[@wtfitsdrewbritton]

Wish I found your videos sooner! Good stuff

[@kyrilkaplan5011]

Excellent teaching : the what and the why...thanks !

[@radioactivepeter]

Excellent video, keep up the good work!

[@user-kq1de9ef2t]

Thank you... perfect explanation!!

[@johnw8154]

this should be trending honestly

[@user-kh4kh2wl9p]

Thanks!!

[@leprofeet9989]

wowie this is useful thanks a lot

[@goodwill7643]

So as I understand, these functions (DMA Channels) are fixed and connected to specific/predefined interfaces like timers, UART or SPI and can be configured only with corresponding interface in order to decries clock cycles for data transfer. In other words I can't choose any random interface on software level and say ok, now do data transfer for ADC for example (if there is no DMA Channel for it). I think I got it. Thank you.

[@Intermation]

Depending on the hardware, you may or may not have the ability to transfer data between any device and memory. I've worked with a number of architectures where you just give the DMA a source address, a destination address, whether to increment, decrement, or leave static each of those addresses with each transfer, and the amount of data to transfer, and it handles the transfer.

[@TNTsundar]

It depends entirely on the DMA engine’s design. You could have mere copiers to more sophisticated ones that understand a lot more context. If the DMA is based on a one-size-fits-all design principle then yes, you could transfer between any peripheral on your chip to any other peripheral or memory.

[@subashsuresh8953]

But sir here we use the arrays that are a run-time storage right, here it's possible for that

[@ayusssapkota327]

How're you writing like that?

[@goncalosousa9691]

That means DMA interact with CPU?

[@natrua100]

why DMA have number of channels? Do they help to increase the speed of transfer?

[@Intermation]

As I've always understood it, a channel is assigned to a specific device. It can be rotated to another device, but only after completing its transfer for the first device.

[@mrsteven1211]

No entendí nada =/

[@Intermation]

I'm guessing you understand a lot more than you think!

[@blainegabriel8906]

I'm Alone 😍😥