Exercise 6.11 Direct Memory Access (DMA) allows devices to access memory directly rather than working through the CPU. This can dramatically speed-up the performance of peripherals, but adds complexity to memory system implementations. Explore DMA implications by answering the questions about the following peripherals.

a. Graphics Card

b. Sound Card 6.11.1 [5] <6.6> Does the CPU relinquish control of memory when DMA is active? For example, can a peripheral simply communicate with memory directly, avoiding the CPU completely?

6.11.2 [10] <6.6> Of the peripherals listed in the table, which would benefi t from DMA? What criteria determine if DMA is appropriate?

6.11.3 [10] <6.6> Of the peripherals listed in the table, which could cause coherency problems with cache contents? What criteria determine if coherency issues must be addressed?

6.11.4 [5] <6.6> Describe what problems could occur when mixing DMA and virtual memory. Which of the peripherals in the table could introduce such problems? How can they be avoided?