UNIVERSITY OF EAST ANGLIA School of Computing Sciences May/June UG Examination EMBEDDED SYSTEMS CMPE3D02. Time allowed: 3 hours

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1 UNIVERSITY OF EAST ANGLIA School of Computing Sciences May/June UG Examination EMBEDDED SYSTEMS CMPE3D02 Time allowed: 3 hours Answer FOUR questions. All questions carry equal weight. Notes are not permitted in this examination. Do not turn over until you are told to do so by the Invigilator. CMPE3D02 Copyright of the University of East Anglia Module Contact: Dr. M. Fisher, CMP Version 1

2 -2-1. (a) What is rate monotonic scheduling? What assumptions does rate monotonic analysis make and how are tasks scheduled? [14 marks] (b) Consider the task set shown in Table 1. Task Computation Time Period A 3 7 B 3 12 C 5 20 Table 1. Task Characteristics (milliseconds) (i) Using rate monotonic task assignment assign priorities to tasks A, B and C. Use larger numbers to represent higher priorities. (ii) Use response time analysis to find the worst case response time for each task. (iii) Do all tasks meet their deadlines? [8 marks] [2 marks] 2. Consider the program shown in Figure 1. Figure 1. C Program (a) Explain the purpose of the program. (b) Assume that register R0 contains the address of the sfrom array, and register R1 has the address of the sto array. Produce an ARM Cortex assembly language version of the C source.

3 -3- (c) From the program in part 2b count the number of data processing, load, store and branch instructions executed for the string CMP UEA. [8 marks] (d) Explain how parameters are passed between the C function and the assembly language subroutine. 3. Imagine that you have a push button switch wired up as shown in Figure 2. Figure 2. Push Button Switch (a) Sketch V out assuming the button is pressed (at t=1) and released (at t=2). What problem is manifest in this circuit? (b) Draw a diagram showing how you would modify the circuit to deal with the problem. Explain how the revised circuit works and how the component values are chosen. (c) By writing pseudo-code, describe how you might deal with this problem in software. Translate your pseudo-code into a C function. Assume the switch is connected to the LSB of port 0xE000E A next-generation digital audio player, powered by an ARM processor, includes connectors to allow the player to be docked with a PC for downloading of music, video clips and photographs. Assuming that the se- TURN OVER

-4- rial port is to be used for docking (Figure 3) and the base address is 0x40004400. Figure 3.

4 -4- rial port is to be used for docking (Figure 3) and the base address is 0x Figure 3. UART Registers (a) Define a C code data structure for the interface device such that each register can be accessed using the (Cortex Microcontroller Software Interface Standard compliant) syntax: USART2->SR; USART2->DR; etc. Explain why the type qualifier volatile should be used in the definition. (b) When docked, the embedded processor is notified that data is available by checking the TXNE bit of the Status Register. (i) Assuming that polling is used and each poll takes 25 clock cycles, and polling can only be allocated a maximum of 5% of total clock cycles, what is the maximum baud rate at which data can be transferred? You may assume a 100MHz CPU, 1 start bit, 2 stop bits and even parity. (ii) Give two reasons why interrupts would be a better choice for this task and explain what steps would be needed to set them (assuming a Nested Vectored Interrupt Controller (NVIC) is used).

5 -5- Why are most of the NVIC control and status registers are only accessible in privileged mode? 5. (a) What is an embedded system? Give a definition and list six example systems. (b) Microcontroller architectures are used in many embedded applications. Describe the typical features of a microcontroller and give examples of the peripherals that it might provide. (c) Many embedded systems target real-time applications. What characterises a real-time embedded system? Give three example real-time applications. (d) Real-time operating systems play an important role in the design of real-time systems. (i) What distinguishes a real-time operating system? (ii) Describe the features you might expect to be provided by a realtime operating system kernel and explain why they are useful. (iii) If a procedure or function is described as re-entrant what does this mean? Why are re-entrant functions particularly important when a real-time kernel is used?. END OF PAPER

Module Contact: Dr Geoff McKeown, CMP Copyright of the University of East Anglia Version 1

Module Contact: Dr Geoff McKeown, CMP Copyright of the University of East Anglia Version 1 UNIVERSITY OF EAST ANGLIA School of Computing Sciences Main Series UG Examination 2015-16 DATA STRUCTURES AND ALGORITHMS CMP-5014Y Time allowed: 3 hours Section A (Attempt any 4 questions: 60 marks) Section