micro:bit Architecture

Question 1

What 4 components create an executable file?

Answer 1

The preprocessor, compiler, assembler and linker

Question 2

What does the compiler do?

Answer 2

It transforms C commands into assembly code

Question 3

What does the assembler do?

Answer 3

Translates assembly code to machine code

Question 4

What is the collective name for the preprocessor, compiler, and assembler?

Answer 4

The compiler

Question 5

What does the linker do?

Answer 5

Combine several object files together that are dependent on one another due to calling function from other files, libraries, header files etc.

Question 6

What are the sections of an object file?

Answer 6

Text section = machine code
Data section = global constants
Relocation information = information about what to modify when linking

Question 7

What happens when the address of a function in unknown?

Answer 7

A placeholder is inserted until the location is known

Question 8

When are placeholders resolved?

Answer 8

During generation of an executable file

Question 9

What does the linker do?

Answer 9

It resolves unknown addresses by using the relocation information stored in the main program and the symbol table which is stored in the not main program

Question 10

Describe the linking process

Answer 10

1. Object files include references to each other’s code and/or data
2. The linker uses relocation records to fill in all addresses
3. The linker combines information from the symbol table and relocation records
4. Assembling to machine code remove all labels form the code

Question 11

Describe static linking of libraries

Answer 11

The library and program are linking by the linker at runtime meaning that the binding between the program and the library is fixed, this also means that if the library is changed you will need to re-link it. Takes up more disk space

Question 12

Describe dynamic linking of libraries

Answer 12

The program and library it references are not combined in the linker. The linker simply places information into the executable and tells the loader the location of shared objects where required code can be found and the references are found during runtime. Two programs can share libraries in memory and you don’t need to re-assemble the whole program

Question 13

Define microcontroller

Answer 13

A compact integrated circuit equipped with one or more central processing units and memory

Question 14

Define embedded system

Answer 14

An electronic product that compromises a microcontroller or multiple microcontrollers executing software instructions stored on a memory module to perform an essential function

Question 15

Micro USB

Answer 15

Streams data to a from the micro:bit and provides power

Question 16

JST connector

Answer 16

Provides power when connected to a 3V battery (2 x 1.5V batteries)

Question 17

ARM Cortex-M4F Processor

Answer 17

Interface that handles USB connection, used for flashing code and data to/from connected devices

Question 18

ARM Cortex-M4 32-bit processor

Answer 18

Contains memory, radio capabilities, and has an integrated temperature sensor

Question 19

BLE antenna

Answer 19

Used for Bluetooth and radio

Question 20

Difference between Bluetooth and Radio capabilities in a micro:bit

Answer 20

Bluetooth allows the micro:bit to talk with central devices only whereas radio allows micro:bit devices to talk to each other so the peripheral can talk to devices other than central devices

Question 21

Motion sensor

Answer 21

Accelerometer and magnetometer, contains the footprint for two sensors (LSM & FXOS) but only one is placed

Question 22

Edge connector

Answer 22

20 pins/strips and 5 rings for connection with external components using crocodile clips or banana plugs

Question 23

Regulator

Answer 23

Steps down to 3.3V

Question 24

Xtal (Crystal)

Answer 24

Electronic crystal oscillator that provides the clock signal

Question 25

SWD bus

Answer 25

Serial wire debug for programming the target MCU

Question 26

UART bus

Answer 26

Universal asynchronous receiver-transmitter for exchanging data with the device connected to the USB

Question 27

I^2C

Answer 27

Integer-integrated circuit bus that allows the main component (target MCU) to communicate with secondary components

Question 28

Define DAPLink

Answer 28

An open-source interface firmware that creates a bridge between the PC and SWD

Question 29

Why does the micro:bit not require a device driver?

Answer 29

It presents itself to the device as a USB disk

Question 30

What happens when you drop code onto the micro:bit when the DAPLink is an interface mode?

Answer 30

The code is written into the target MCU flash memory

Question 31

What is DAPLink bootloader mode?

Answer 31

Used to update the version of the DAPLink and the code is written to the interface MCU flash and updates the version of the DAPLink

Question 32

Describe the divide and conquer method for debugging

Answer 32

Removing and adding code to monitor when your program works and when it breaks to indicate where the bug is

Question 33

Describe logging method of debugging

Answer 33

Inserting printf to determine the state of your program in different locations to find the bug

Question 34

What are the disadvantages of logging as a debugging method?

Answer 34

1. Not efficient 2. Requires a lot of memory 3. Can cause a heisenbug

Question 35

What is a heinsenbug?

Answer 35

A bug that occurs when you remove a printf statement and and error occurs

Question 36

Why does a heisenbug happen?

Answer 36

Removing a printf statement causes memory allocation to change and the stack will be affected triggering bus errors

Question 37

Define big endian

Answer 37

The MSB is stored first

Question 38

Define little endian

Answer 38

The LSB is stored first

Question 39

What class do you use to perform debugging by logging for a micro:bit?

Answer 39

The serial class

Question 40

What does the flag -g do?

Answer 40

Tells the compiler to generate and embed debug symbols which include names of functions, file names, and line numbers of errors

Question 41

What does the Stack pointer point to?

Answer 41

The lowest address of the stack for the current frame which will be the top of the stack

Question 42

What does the base/frame pointer point to?

Answer 42

A reference address of the previous frame

Question 43

What does the instruction pointer point to?

Answer 43

The address that the function will return to

Question 44

What does stack memory contain?

Answer 44

Stack frames that include data needed by function calls including argument and local variables

Question 45

What does heap memory contain?

Answer 45

Data used for variables within the program that have a dynamic size

Question 46

What is the Block Starting Symbol (BSS) section of memory used for?

Answer 46

Global variables that are initialised to 0 or do not have explicit initialisation

Question 47

What is the DATA section of memory used for?

Answer 47

Global variables that have been intitialised

Question 48

What does the TEXT section of memory contain?

Answer 48

The binary executable instructions of a program

Question 49

What are the pointers contained within a stack frame?

Answer 49

Stack pointer, frame/based pointer, saved instruction pointer

Question 50

What does the OS Kernel memory contain?

Answer 50

Memory reserved by the OS to monitor and control mapping between virtual and physical addresses

Question 51

What is the translation lookaside buffer?

Answer 51

A specialised cache that contains recent virtual-to-physical address translations so that the CPU can quickly retrieve them without having to refer to the table again

Question 52

What is the difference between RAM and DAM?

Answer 52

Accessing memory addresses in DAM it takes longer because it linearly searches through each memory address to find one

Question 53

Which component handles virtual-to-physical address translation?

Answer 53

The Memory Management Unit