7,157 views
9 votes
9 votes

A processor is fetching instructions at the rate of $1$ MIPS. A DMA module is used to transfer characters to RAM from a device transmitting at $9600$ bps. How much time will the processor be slowed down due to DMA activity?

  1. $9.6$ms
  2. $4.8$ms
  3. $2.4$ms
  4. $1.2$ms

5 Answers

Best answer
10 votes
10 votes

 External Device sends data to DMA module in 1 sec =9600 bits

                                                                              =9600/8=1200 Bytes

Now Processor runs instructions in 1 second= 1 Million  (because 1 MIPS means 1 million instructions per second)

                                                                = 10 ^ 6

So time will the processor be slowed down due to DMA activity =  1200 / (10^6)= 0.0012 seconds

                                                                                                                                = 1.2 ms

selected by
6 votes
6 votes

DMA usually operates in cycle stealing mode, where it transfers 1 byte per cycle. //Default assumption.

So, given DMA bandwidth = 9600bps = 1200 bytes per sec.

1 MIPS = 1 Million Instructions Per Second.

So, normally, CPU fetches $10^6$ instructions each second.

Now, CPU can fetch $10^6 - 1200$ instructions per second. //Assumption 1 instruction = 1B

Rate of change = $\frac{10^6-(10^6-1200)}{10^6}$ = $\frac{1200}{10^6}$ = $1.2*10^{-3}$

 

Option D

3 votes
3 votes

Assuming Data Width of the System bus is Byte,DMA Will run every Cycle for every Byte.which has arrived.

So,

10^6 bits  in   1 second
1 bit   in 1/10^6 second
9600 bits in    9600* 1/10^6 seconds
9600/8 bytes in    9600/8* 1/10^6 seconds

Which gives 1.2 ms  or 1MIPS..

Option D)

 

0 votes
0 votes
Assuming Instruction size = 1 byte.

Processor speed = 1MIPS

 It can fetech in 1 sec 10^6 byte.

With DMA it can fetech in 1 sec 1200 byte.

% of slow down = 1200*100/10^6 = .12%
Answer:

Related questions

3 votes
3 votes
2 answers
1
makhdoom ghaya asked Apr 27, 2016
3,597 views
In 8085 microprocessor, the ISR for handling trap interrupt is at which location?$3CH$$34H$$74H$$24H$
5 votes
5 votes
5 answers
2
makhdoom ghaya asked Apr 27, 2016
3,822 views
How many number of times the instruction sequence below will loop before coming out of the loop? MOV AL, 00H A1: INC AL JNZ A11255256Will not come out of t...
2 votes
2 votes
3 answers
3
makhdoom ghaya asked Apr 27, 2016
4,410 views
In $8086$, the jump condition for the instruction $JNBE$ is?CF = 0 or ZF = 0ZF = 0 and SF = 1CF = 0 and ZF = 0CF = 0
8 votes
8 votes
5 answers
4
makhdoom ghaya asked Apr 26, 2016
10,110 views
How much speed do we gain by using the cache, when cache is used $80$% of the time? Assume cache is faster than main memory.$5.27$$2.00$$4.16$$6.09$