EE 472 Embedded Systems. Name solutions. Instructions:

Transcription

1 Name solutions Instructions: Write your name and student id on every page. You may not consult any other materials or anyone in the class. If you are unsure of what a question is asking, write your assumptions next to the question, and they will be taken into consideration in grading. You have the entire class period to finish the exam. Please show your work where applicable. Please write neatly! If I can t read your answer, I won t be able to give you credit. Good luck! Points: Worth 100 total points Grade: out of 100 Page 1 of 9

2 1. Evaluate the following expressions below (give answers in binary): (10 points) #define A #define B #define C #define D #define E unsigned char a,b,c,d; a =!A B ~C ; b = (B & C) << 3 ; c = (A && C) C ; d = (B << 1) A ; e = (B & C A) >> 3 ; a = b = c = d = e = Page 2 of 9

3 2. What is the output of the following code? (15 points) int main( void ){ int a=10,b=9,c=8; int d[5] = {1,5,3,8,0}; int *p1, *p2, *p3; int x,y; p2=&b; p3=&d[2]; p1=p3; *p3 = --(*(++p1)); x = *(p1+1) + *p2 + c; y = d[4] + *p3; printf("%d %d %d %d %d\n", x, y, *p1, *p2, *p3); return 0; } Page 3 of 9

4 3. Write out the code for the following. (10 points) Write a function called swap_structs, which takes in two drone structs by reference and swaps the entire contents of the two except for the char* data. //assume this struct typedef struct drone{ } drone; char* name; int calibration_data[50]; int* memory_map[10]; int (*test_seq)(int, int)); void swap_structs(drone* a, drone* b){ int* temp_cal; int** temp_mem; int (*temp_func)(int, int)); temp_cal = a->calibration_data; temp_mem = a->memory_map; temp_func = a->test_seq; a->calibration_data = b->calibration_data; a->memory_map = b->memory_map; a->test_seq = b->test_seq; b->calibration_data = temp_cal; b->memory_map = temp_mem; b->test_seq = temp_func; // 3pts for setting up temp variables correctly // 3pts for correctly dereferencing the drone structs // 4pts for correctly swapping the contents // just swapping the drone pointers does not work (-8) // deep copy is OK (-1) } Page 4 of 9

5 4. Short Answer. Write your brief response to each question in the space provided. (20 total points) a. What is a context switch and when does it occur? (5 points) Occurs when a task is preempted or during an interrupt (2pts). The current state of the task needs to be saved (i.e. variables, program counter, stack, etc) before switching to the new task (3pts). b. What is an ISR? What C concept is typically used to refer to an ISR? (5 points) The interrupt service routine is the operation or function that is executed when an interrupt occurs (2pts). It is usually a quick function that is referenced by a function pointer (3pts) in an interrupt vector table. Page 5 of 9

6 c. Why is UML important and describe one type of UML diagram? (5 points) Provides engineers and developers a common language to specify designs (i.e., standard way of describing a design). (3pts) Types of diagrams: use case, sequence, class, activity, etc. (2pts) d. In class, we discussed various attributes found in a Task Control Block (TCB) for a task. Name three pieces of information that you might find in a TCB. (5 points) Pointer to the task, status or state, data for the task, program counter, etc. Page 6 of 9

7 5. Scheduling Problems. Write your response to the question in the space provided. (45 total points) PART 1 (Next 2 pages) Consider the following three tasks with a non-preemptive, round robin scheduler. In this scheduler, if a task issues the command OS_delay(int d), the scheduler will immediately run and will not restart that task until at least d time ticks have passed. Task A: C = 233 µs, P=3.0ms., D=P. Task B: C = 233 µs, P=2.0ms., D=P. Task C: The structure of Task C is for(i=0;i<3;i++) { compute for 233 µs OS_delay(1); Make I/O Request that takes 666 µs; } Halt(); Make the following assumptions: The scheduler may not run a task if the task has completed its computation but has not yet reached its period (i.e., synchronous) Assume the scheduler does not run between a delay and I/O if the I/O immediately follows a delay. If no task can run, the scheduler waits until a task can run. Periods and delay values are only measured by OS time ticks. (integer multiples of 1ms.) The scheduler takes 100 µs of CPU time. Assume the scheduler starts for the first time at t = 0. Page 7 of 9

8 a. Fill out the scheduling diagram for these three tasks through at least t=8 ms. (25 points) b. Are the deadlines for Task A and B met? (5 points) yes Page 8 of 9

9 PART 2 Consider the following three tasks with a preemptive priority-based scheduler. Task A: P = 2 ms, C = 1 ms, repeats 3 times then Halts. Task B: C = 233 micro sec, then delays for 2 ms, and then the entire task repeats Task C: Runs forever a. What priority values would you assigned to tasks A, B, and C (with 1 being the highest and 3 being the lowest)? (5 points) A 2 1 B 1 or 2 C 3 3 b. Why? (5 points) Task C must be the lowest priority or nothing else will run. c. After running your scheduler, you find that task B is running too often. What could you do to reduce its frequency? (5 points) Add a delay or increase the period of the task. DO NOT change the priority. Page 9 of 9

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