Answer to Question #270226 in Electrical Engineering for sam

Question

A DMA controller transfers 32 bit words to memory using cycle stealing. The words are assembled from a device that transmits characters at a rate of 2400 characters per second. Each character is 8 bit length. The CPU is fetching and executing instructions at an average rate of 1 million instructions per second. By how much will the CPU be slowed down because of the DMA transfer?

Answer 1

32 bit word= 4byte

9600 bytes in 1 sec

so for 1 byte it takes 1/9600 sec

so for 4 byte word it takes 1/2400 sec

so 2400 words are transfered in 1 sec through cycle stealing and given 1 million instructions (MIPS) are fetching and executing in 1 sec out of which 2400 words are executing through cycle stealing so percentage (%) of slow down or cycle wasted in dma transfer = (2400/1000000)*100 =0.24%

Answer : 0.24 %