ECE495k Final Sample Soln.

Transcription

1 Final Sample Soln. ECE495k ECE495k Final Sample Soln. May NAME: There are?? pages (including this one) in this exam. Assessment: This exam is worth a total of 100 points. There are a total of?? problems, some with several subproblems. Each question should take no more than 15 minutes. Procedures: Work on this exam alone. You may not use your class notes, class handouts, course text, or any other external materials while taking this exam. Submit the exam to the instructor at the end of class. Limit your answers to the space provided, if possible. If not, write on the back of the same sheet and indicate that you have done so. If absolutely needed, you may attach additional pages, but please write your name and the problem/subproblem number on each attached page. Read all problems carefully before attempting solutions. Be sure to state all your assumptions, but make as few assumptions as possible. Page 1 of??

2 Final Sample Soln. ECE495k 1 LOGIC DESIGN(12 POINTS) 1 Logic Design(12 points) Convert this expression to NAND and NOT: f = x.y.z + x.y.z + x.y.z Hint: Use DeMorgan s Law to convert OR to NAND. f = (NAND(x,y,z)) NAND (NAND(x, y, z )) NAND (NAND(x, y, z )) Page 2 of?? Problem #1

3 Final Sample Soln. ECE495k 2 LC-3 ASSEMBLY (13 POINTS) 2 LC-3 Assembly (13 points) Write an LC-3 routine to add two numbers, called number1 and number2, stored in memory and return the result in register R0. Before return, your routine should ensure that all the registers (except R0) are what they were at the time of calling this routine. You must use the stack to save and restore registers. Assume that R6 points to the top of the stack (the top slot pointed to by R6 h as useful data and should not be overwritten). Recall that pushes decrement the stack pointer in LC-3. You can assume that the stack has been declared for you. Hint: Write the body of the routine first and then write the saves and restores. When you write the body, leave some space above and below the body for the save/restore code. add r6, r6, #-3 str r7, r6, #2 str r1, r6, #1 str r2, r6, #0 ld r1, number1 ld r2, number2 add r0, r1, r2 ldr r2, r6, #0 ldr r1, r6, #1 ldr r7, r6, #2 add r6, r6, #3 ret number1.blkw 1 number2.blkw 1 Page 3 of?? Problem #2

4 Final Sample Soln. ECE495k 3 SIMPLE C PROGRAM (15 POINTS) 3 Simple C Program (15 points) Write a C program to compute the sum of integers from 1 to n, where n is input from the keyboard. The program should print the sum. #include<stdio.h> int main() { int i; int n; int sum = 0; printf("please input the number n: "); scanf("%d", &n); for (i=0; i<= n; i++) sum += i; } printf("the sum is %d\n", sum); Page 4 of?? Problem #3

5 Final Sample Soln. ECE495k 4 C CONSTRUCTS (10 POINTS) 4 C Constructs (10 points) What is the output of the following code segment? j = 2; for (i = 0; (i < 2) (j < 6) ; i++) { printf ("%d ", i); j++; } Page 5 of?? Problem #4

6 Final Sample Soln. ECE495k 5 ARRAYS/POINTERS (15 POINTS) 5 Arrays/Pointers (15 points) Write a C function to convert a character stored in memory to capital if the character was small and do nothing to the character if it was already capital or if it is a non-letter character. The function takes as input a pointer to the character and has no return value. void convert(char *s) { if ((*s >= a ) && (*s <= z )) *s += a - A ; } Page 6 of?? Problem #5

7 Final Sample Soln. ECE495k 6 RECURSION (15 POINTS) 6 Recursion (15 points) Write a recursive C function, arraysum, to compute the sum of n numbers in an array A[] as follows: sum of n numbers A[0 to n-1] = A[0] + sum of n-1 numbers A[1 to n-1]. arraysum is declared as follows where currentelement points to the current array element to be added and last element points to the last element of the array: int arraysum(int *currentelement, int *lastelement); And main() calls arraysum as follows: sum = arraysum(&a[0], &A[n-1]); int arraysum(int *currentelement, int *lastelement) { if (currentelement == lastelement) return (*currentelement); else return (*currentelement + arraysum(currentelement+1, lastelement); } Page 7 of?? Problem #6

8 Final Sample Soln. ECE495k 7 MULTICORE (20 POINTS) 7 Multicore (20 points) In the lecture slides example on joint account, what goes wrong when two people withdraw at about the same time from the account? The steps for withdrawal are: read balance verify balance greater than withdrawal amount else fail dispense withdrawal amount subtract withdrawal amount from balance update balance The problem is that two withdrawals in parallel will interleave in arbitrary ways and before one withdrawal updates the balance, the second may read the previous balance which can cause incorrect verification for the second withdrawal. The second withdrawal will later update the balance which will not. reflect the first withdrawal, leaving an incorrect balance at the end. How would you fix the above steps to avoid the problem? Write the new steps below. lock account read balance verify balance greater than withdrawal amount else fail dispense withdrawal amount subtract withdrawal amount from balance update balance unlock account Page 8 of?? Problem #7