Past Paper (2018)

Question One

Q1A

Question

What is a Program Counter? Explain how a program counter is used in a microcontroller.

A program counter is a location in the hardware which stores the index of the current instruction. Branching in code is performed by changing the value of the program counter.

Q1B

Question

What is the main difference between a microcontroller unit (MCU) and a microprocessor unit (MPU)? List three disadvantages of an MPU.

Answer

An MCU is a combination of a processing unit and hardware inferfaces such as digital IO ports, ADCs, and peripheral interfaces. An MPU (while much more powerful), typically only contains the processor.

Q1C

Question

Find the odd and even components of the given signal $f(s)$.

$$x(t)=1+tcos(5)+5(t{)}^3$$

Not relevant.

Question Two

INSET DIAGRAM HERE! Figure 1.

Q2A

Question

Why does AVR adopt a Harvard architecture? Justify your answer using figure 1.

The Harvard architecture separates the program memory from the data memory, as opposed to the von Neumann architecture which combines both. AVR micro controllers use the Harvard architecture because they have very small amounts of program and data memory, and keeping them seperate allows for the MCU to use different bus widths for instructions vs data. (i.e. 8 bit instructions, 16 bit data.).

Q2B

Question

The central processing unit (CPU) consists of arithmetic logic unit (ALU), General Purpose Registers, Status Registers, Program Counter, Instruction Register, Instruction Decoder. What is the purpose of using Status Registers? Explain how Status Registers are used in AVR.

Status registers allow for a simple, high performance method of checking the status of different peripheral devices. Because checking or changing the status registers can be performed as bit-operations, doing so is extremely performant.

Q2C

Question

What are the basic operations of ALU in AVR?

• Addition
• Subtraction
• Multiplication
• Division
• Logical operations (AND, OR, XOR, NOT)

Q2D

Question

What is the main advantage of General Purpose Registers over Random Access Memory (RAM). Justify your answer.

General Purpose Registers are non-memory-mapped registers that can be used to store, access, and manipulate data in the MCU extremely quickly (typically operations can be completed within a single instruction cycle).

Question Three

A quadcopter, also known as a quadrotor helicopter, is a helicopter that is lifted and propelled by four rotors. As compared to conventional helicopters, quadcopters have smaller blades, thus less kinetic energy, reducing their ability to cause damage. Suppose you are working as an Embedded System Engineer in SkyFly, a company that designs and manufacturers unmanned aerial vehicles (UAVs), including quadcopters. Your current project is to design a simple quadcopter, as illustrated in Figure 2, with the following requirements: (1) The quadcopter is driven by four brushless DC motors, capable of a collective thrust of 400g using a 11V Lithium-Polymer (LiPo) battery. (2) Each motor is driven by a brushless electronic speed controller (ESC), with the control signal from the avionics printed circuit board (PCB). (3) The Avionics PCB generates the control signal based on a combination of sensor feedback collected from inertial measurement unit (IMU) and the received signal from a remote controller. (4) The quadcopter communicates with the remote controller through a Bluetooth module. (5) A voltage regulator board is used to convert the 11 V power supply to 5 V and a 3.3 V for auxiliary purpose. (6) The components are mounted on a frame made of carbon-fiber composite material with a foam core for its durability, low weight and bending stiffness.

INSET DIAGRAM HERE FIGURE 2

Q3A

Question

Suppose you have chosen the following components from Element 14: (1) the InvenSense MPU-6050 sensor for IMU; (2) DualSky XC406ULT for ESCs; (3) Panasonic Bluetooth module PAN1321. The datasheets for the above devices are provided in the appendices (Appendix A-C). Using the datasheets, together with the specifications for the quadcopter, draw a hardware block diagram including all major components, and where applicable, the connection type between the MCU and the peripheral (e.g. logic level / analogue voltage / SPI / UART / I2C).

Q3B

Question

What are the factors that you need to consider when selecting a microcontroller for this quadcopter design? Justify your answer.

Q3C

Question

For the software development of the quadcopter, which software architecture is more suitable? Justify your answer.

Q3D

Question

Suppose the customer requires recording the real-time flight trajectory of the quadcopter. How will you revise your design?

Depending on the accuracy required, the design may not require revision. Given the onboard IMU, the trajectory can be estimated using dead-reckoning. My concern would be recording the data, but if the bluetooth connection is fast enough we may simply transmit measurements from the IMU and reconstruct the path on the control device.

Question Four

Q4A

Question

What is Just-In-Time compilation? What is its main advantage?

Just-In-Time compilation is a technique where code is compiled at run-time by a JIT compiler. This allows the compiler to optimize the code for the specific hardware it is running on.

Q4B

Question

What is a namespace? How are namespaces used in .NET?

Namespaces are used to organize code into logical groups and avoid naming conflicts.

Q4C

Question

Explain the main difference between managed and unmanaged code?

Managed code is code that is executed by the .NET runtime, while unmanaged code is code that is executed by the operating system.

Question Five

Object Oriented Programming (OOP) creates objects / classes to modularize the code.

Q5A

Question

Explain the main difference between a class and an object.

An object is a specific instantiation of a class.

Q5B

Question

What are the two purposes of encapsulation in OOP?

Encapsulation is when access to the methods or properties of a class is restricted.

This improves security and allows controlled access to those methods and properties.

Q5C

Question

What is constructor overloading in OOP?

Constructor overloading allows a class to have multiple constructors with different parameter lists.

Q5D

Question

What is a derived class?

A derived class is a class that inherits the properties and methods of its parent class.

Q5E

Question

Explain how protected access is used in OOP.

The protected keyword in C# indicates that a method or property may be accessed only by a class or its derived classes.

Question Six

Code analysis is an important skill for software engineers. Answer the following questions in the context of OOP.

Q6A

Question

What is the purpose of having two keywords virtual and override in the following piece of C# code?

namespace system {
    class Object {
        public virtual string ToString() {
            // Default code.
        }
    }
 
    class Circle : System.Object {
        public override string ToString() {
            // Your code here
        }
    }
}

The virtual keyword indicates that a method may be overridden, and the override keyword indicates that a method is intended to override another.

Q6B

Question

When do we use sealed classes?

Sealed classes are used when we want to prevent a class from being inherited.

Q6C

Question

How is memory management achieved in .NET? Explain the two major steps to reclaim memory.

C# is a garbage-collected language, meaning that memory is automatically reclaimed when it is no longer needed.

The two steps are:

1. The .NET framework detects that there are no more active references to an object.
2. The garbage collector reclaims the memory used by the object.

Q6D

Question

Write a C# class definition with appropriate comments for managing banking accounts through a C# application. The class with the name BankAccount should include the following:

1. One private data member owner with type string.
2. One private data member balance with type decimal.
3. One private data member interestRate with type double.
4. One default constructor that accepts a string, a decimal, and double, and uses these to create a new bank account.
5. One overloaded constructor that accepts a string and a double to open a bank account with a balance of 0.0.
6. A public virtual method Balance that reads the balance value of the bank account.
7. A public virtual method Withdraw that accepts the decimal withdraw amount, and deducts the withdraw amount from the balance amount.
8. A public virtual method Deposit that accepts the decimal deposit amount, and adds the deposit amount to the balance amount.
9. A public virtual method AddInterests adds the corresponding interests to the balance amount (e.g. at the end of the year.)

namespace Q6 {
    class BankAccount {
        private string owner;
        private decimal balance;
        private double interestRate;
 
        public BankAccount(string owner, decimal balance, double interestRate) {
            this.owner = owner;
            this.balance = balance;
            this.interestRate = interestRate;
        }
 
        public BankAccount(string owner, double interestRate) {
            this.owner = owner;
            this.balance = 0.0m;
            this.interestRate = interestRate;
        }
 
        public decimal Balance {
            get { return balance; }
        }
 
        public void Withdraw(decimal amount) {
            balance -= amount;
        }
 
        public void Deposit(decimal amount) {
            balance += amount;
        }
 
        public void AddInterests() {
            balance += (decimal)interestRate * balance;
        }
    }
    
}