DMA

• Consider a disk read example: a block in disk is being
read into memory
• For each word, the CPU does a
lw [destination register] [I/O device address] and a
sw [data in above register] [memory-address]
• This would take up too much of the CPU’s time – hence,
the task is off-loaded to the DMA controller – the CPU
informs the DMA of the range of addresses to be copied
and the DMA lets the CPU know when it is done

• Pertimbangkan membaca disk contoh: sebuah blok di disk yang
baca ke memori
• Untuk setiap kata, CPU melakukan
lw [tujuan daftar] [I / O device alamat] dan
sw [data di atas daftar] [alamat memori]
• Hal ini akan mengambil terlalu banyak dari waktu CPU - karenanya,
tugas off-load ke DMA controller - CPU
menginformasikan kepada DMA dari kisaran alamat yang akan disalin
dan DMA memungkinkan CPU tahu kapan itu dilakukan