Embedded-Hacking/WEEKS/WEEK04/QUIZ04.md

# Week 4 Quiz: Variables, Memory Sections, and GPIO

## Instructions
Choose the best answer for each question. There is only one correct answer per question.

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## Questions

### Question 1
Which memory section contains initialized global variables (e.g., `int counter = 42;`)?

A) `.bss`  
B) `.text`  
C) `.data`  
D) `.rodata`  

> 📖 **Reference:** Week 4, Part 2 – "The Three Main Sections"

**Correct Answer: C**

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### Question 2
What is the data type `uint8_t`, and what is its valid value range?

A) Signed 8-bit integer; -128 to 127  
B) Unsigned 8-bit integer; 0 to 255  
C) Unsigned 16-bit integer; 0 to 65,535  
D) Signed 16-bit integer; -32,768 to 32,767  

> 📖 **Reference:** Week 4, Part 1 – "Understanding Data Types" (data types table)

**Correct Answer: B**

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### Question 3
In the intro-to-variables program, the original code sets `age = 42` then immediately sets `age = 43`. In the compiled binary, what value appeared and why?

A) `42`, because the first assignment always takes precedence  
B) Both `42` and `43`, because the compiler keeps all assignments  
C) `43` only, because the compiler optimized out the unused value `42`  
D) `0`, because the variable was placed in the BSS section  

> 📖 **Reference:** Week 4, Part 8, Step 15 – "Understand the Optimization"

**Correct Answer: C**

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### Question 4
When analyzing a raw `.bin` file in Ghidra (without debug symbols), what base address must you set when importing RP2350 firmware?

A) `0x00000000`  
B) `0x20000000`  
C) `0x10000000`  
D) `0x00100000`  

> 📖 **Reference:** Week 4, Part 6, Step 7 – "Configure the Binary Format"

**Correct Answer: C**

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### Question 5
Why do uninitialized global variables (e.g., `uint8_t age;`) always print `0` in the uninitialized-variables example?

A) The C compiler sets all uninitialized variables to 0 before generating machine code  
B) The startup code (reset handler) zeros out the entire BSS section before `main()` runs  
C) The Pico SDK automatically initializes all variables through `stdio_init_all()`  
D) Uninitialized variables are stored in flash memory which always reads as 0  

> 📖 **Reference:** Week 4, Part 2 – "What Happens to Uninitialized Variables?"

**Correct Answer: B**

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### Question 6
What is the purpose of the `uf2conv.py` script used in Week 4?

A) It decompiles a UF2 binary back into C source code  
B) It converts a raw `.bin` file into the UF2 format required to flash the Pico 2  
C) It compresses the firmware binary to fit within flash memory limits  
D) It strips debug symbols from an ELF file to create a raw binary  

> 📖 **Reference:** Week 4, Part 10, Step 19 – "Convert to UF2 Format"

**Correct Answer: B**

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### Question 7
Which Pico SDK function sets a GPIO pin's direction to output?

A) `gpio_init(pin)`  
B) `gpio_put(pin, value)`  
C) `gpio_set_dir(pin, GPIO_OUT)`  
D) `gpio_enable(pin, OUTPUT)`  

> 📖 **Reference:** Week 4, Part 3 – "GPIO Functions in the Pico SDK" (table)

**Correct Answer: C**

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### Question 8
What does `gpio_put(LED_PIN, 1)` do to an LED connected to that GPIO pin?

A) It reads and returns the current voltage level of the pin  
B) It initializes the GPIO pin and registers it for output use  
C) It drives the pin HIGH, turning the LED on  
D) It drives the pin LOW, turning the LED off  

> 📖 **Reference:** Week 4, Part 3 – "GPIO Functions in the Pico SDK" and Part 11, Step 22

**Correct Answer: C**

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### Question 9
What hexadecimal value does `0x2b` represent, and why did it appear in the compiled binary for the intro-to-variables program?

A) `0x2b` = 42; it is the first value assigned to `age`  
B) `0x2b` = 43; it is the optimized constant that replaced the `age` variable  
C) `0x2b` = 44; it is the address of the `age` variable in SRAM  
D) `0x2b` = 27; it is a stack offset calculated by the compiler  

> 📖 **Reference:** Week 4, Part 8, Step 15 – "Understand the Optimization" (0x2b = 43 decimal)

**Correct Answer: B**

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### Question 10
What does the `--family 0xe48bff59` argument specify when running `uf2conv.py`?

A) The base address of the XIP flash region  
B) The CRC checksum of the compiled binary  
C) The RP2350 chip family identifier required by the UF2 format  
D) The baud rate used for serial communication  

> 📖 **Reference:** Week 4, Part 10, Step 19 – "Convert to UF2 Format"

**Correct Answer: C**

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## Answer Key

1. C - Initialized global variables belong to the `.data` section
2. B - `uint8_t` is an unsigned 8-bit integer with range 0 to 255
3. C - The compiler optimized out the unused `42` assignment, keeping only `43` (0x2b)
4. C - RP2350 firmware loads at the XIP base address `0x10000000`
5. B - The reset handler's BSS clear phase zeros all uninitialized global variables before `main()` runs
6. B - `uf2conv.py` converts a raw `.bin` file to the UF2 format the Pico 2 uses for flashing
7. C - `gpio_set_dir(pin, GPIO_OUT)` configures the pin direction as output
8. C - `gpio_put(pin, 1)` drives the pin HIGH, turning the LED connected to that pin on
9. B - `0x2b` = 43; the compiler replaced the `age` variable entirely with this constant
10. C - `0xe48bff59` is the RP2350 family ID embedded in the UF2 file header

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## Scoring Guide

- **10 correct**: Excellent! You have a strong grasp of Week 4 concepts
- **8-9 correct**: Very good! Review the topics you missed
- **6-7 correct**: Good start. Go back and review the key concepts
- **5 or fewer**: Review the Week 4 material again and try the practice exercises

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## Topics Covered

This quiz tests your understanding of:
- Memory sections: `.data`, `.bss`, `.rodata`, and `.text`
- Data types: `uint8_t` size and range
- Compiler optimization of unused variable assignments
- Importing raw `.bin` files into Ghidra with the correct base address
- BSS zero initialization at startup
- UF2 format and the `uf2conv.py` conversion script
- GPIO functions: `gpio_init()`, `gpio_set_dir()`, `gpio_put()`
- GPIO control: `gpio_put()` behavior (HIGH/LOW)
- Hexadecimal to decimal conversion in context
- UF2 family IDs for chip identification