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DMA Programming Tutorial 1

A brief 9 page guide on DMA programming in C

(by justin deltener)

This 9 page PDF document introducing the programming of 8237 DMA chip using C.


This article is online from 2913 days and has been seen 8899 times




DMA Programming Tutorial 1

Intro

DMA or Direct Memory Access gives us the ability to move large amounts of memo
ry from one place to another VERY quickly. 
It takes some CPU usage to set up the DMA tranfer, but after that, the DMA and
 the recipient finish without involving the CPU! 
This is what makes sound playback at 44khz a reality. 
Without DMA weíd be struggling to do anything while the sound was playing! 
Any computer will have 2 DMAC or 8237 DMA Controllers in which 1 is used for 8
 bit transfers and the other for 16 bit transfers. 
If you are reading (or attempting to read) this tutorial, Iím going to assume 
that you are familiar with writing to ports, if youíre not this might be a lit
tle confusing (if not impossible). 
Since we know that a normal computer has 2 DMACís lets take a look at which po
rts we will be using to communicate with them!

DMAC Ports
All these ports, Address and Count, what the heck does it all mean! Later on w
hen we set up the DMA
transfer we will be telling the DMA where our memory is comming from, thatís w
here the address port
comes into use. We wonít need to tell it to go the Sound Blaster card, the har
dware will do that for us.
We will also need to tell it how much to transfer, thatís where the count port
 comes in!

(*** download for full text ***)



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 Tags: 8237, dma


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