Logic analyzer for signal debugging in Embedded C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the logic analyzer input pin.

Embedded C

void init_logic_analyzer() {
    DDRD &= ~[1]; // Set PD2 as input
}

Drag options to blanks, or click blank then click option'

A(1 << PD4)

B(1 << PD2)

C(1 << PD3)

D(1 << PD5)

Attempts:

3 left

💡 Hint

Common Mistakes

Setting the wrong bit for the input pin.

Using |= instead of &= ~ to clear the bit.

We clear the bit for PD2 in DDRD to set it as input.

2fill in blank

medium

Complete the code to read the logic analyzer input pin state.

Embedded C

uint8_t read_signal() {
    return (PIND & [1]) ? 1 : 0;
}

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A(1 << PD2)

B(1 << PD3)

C(1 << PD4)

D(1 << PD5)

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong pin mask.

Not using bitwise AND operator.

We mask PIND with (1 << PD2) to read the state of PD2 pin.

3fill in blank

hard

Fix the error in the code to store signal samples in the buffer.

Embedded C

void sample_signal(uint8_t *buffer, uint16_t length) {
    for (uint16_t i = 0; i < length; i++) {
        buffer[i] = [1];
    }
}

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Aread_signal()

Bread_signal

C*read_signal()

D&read_signal()

Attempts:

3 left

💡 Hint

Common Mistakes

Using function name without parentheses.

Dereferencing the function pointer incorrectly.

We must call the function read_signal() to get the current signal value.

4fill in blank

hard

Fill both blanks to configure the timer for sampling at 1 kHz frequency.

Embedded C

void setup_timer() {
    TCCR1B = (1 << [1]) | (1 << [2]); // Prescaler 64
    OCR1A = 249;
    TIMSK1 = (1 << OCIE1A);
}

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ACS11

BCS10

CCS12

DWGM12

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong CS bits for prescaler.

Confusing WGM bits with CS bits.

Setting CS11 and CS10 bits in TCCR1B sets the prescaler to 64 for the timer.

5fill in blank

hard

Fill all three blanks to implement the interrupt service routine that stores samples.

Embedded C

ISR(TIMER1_COMPA_vect) {
    static uint16_t index = 0;
    if (index < [1]) {
        sample_buffer[[2]] = [3];
        index++;
    }
}

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ABUFFER_SIZE

Bindex

Cread_signal()

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names.

Not calling read_signal() function.

The ISR stores samples in sample_buffer at position index until BUFFER_SIZE is reached, reading the signal each time.

Practice

1. What is the main purpose of a logic analyzer in embedded C programming?

easy

A. To increase the clock speed of the microcontroller

B. To capture and display digital signal changes for debugging

C. To compile the embedded C code faster

D. To store large amounts of data permanently

Solution

1. Step 1: Understand the role of a logic analyzer

   A logic analyzer is a tool used to observe digital signals and their timing to find bugs in hardware or software.

2. Step 2: Match the purpose with the options

   Only To capture and display digital signal changes for debugging describes capturing and displaying digital signals for debugging, which matches the logic analyzer's purpose.

3. Final Answer:

   To capture and display digital signal changes for debugging -> Option B

4. Quick Check:

   Logic analyzer = signal capture and debugging [OK]

Hint: Logic analyzers show signals, not speed or storage [OK]

Common Mistakes:

• Confusing logic analyzer with compiler tools
• Thinking it increases microcontroller speed
• Assuming it stores data permanently

2. Which of the following code snippets correctly reads a digital input pin for logic analysis in embedded C?

easy

A. int signal = digitalRead(PIN);

B. int signal = PIN.read();

C. int signal = readDigital(PIN);

D. int signal = digital_input(PIN);

Solution

1. Step 1: Identify standard embedded C syntax for reading pins

   In embedded C, reading a digital pin often uses a function like digitalRead(pin) returning the pin state.

2. Step 2: Compare options to common embedded C functions

   Only int signal = digitalRead(PIN); uses the correct function digitalRead with the pin as argument.

3. Final Answer:

   int signal = digitalRead(PIN); -> Option A

4. Quick Check:

   digitalRead(pin) is standard pin read [OK]

Hint: Look for standard function digitalRead(pin) syntax [OK]

Common Mistakes:

• Using object-oriented syntax not valid in C
• Inventing non-standard function names
• Missing parentheses in function calls

3. Given the code below, what will be the content of the buffer after execution?

int buffer[4];
for(int i = 0; i < 4; i++) {
    buffer[i] = (i % 2) ? 1 : 0;
}

medium

A. [0, 1, 0, 1]

B. [1, 0, 1, 0]

C. [0, 0, 0, 0]

D. [1, 1, 1, 1]

Solution

1. Step 1: Analyze the loop and condition

   The loop runs i from 0 to 3. For each i, buffer[i] is set to 1 if i is odd (i % 2 == 1), else 0.

2. Step 2: Calculate values for each i

   i=0: 0%2=0 -> buffer[0]=0
   i=1: 1%2=1 -> buffer[1]=1
   i=2: 2%2=0 -> buffer[2]=0
   i=3: 3%2=1 -> buffer[3]=1

3. Final Answer:

   [0, 1, 0, 1] -> Option A

4. Quick Check:

   Odd i -> 1, Even i -> 0 [OK]

Hint: Remember i%2 is 0 for even, 1 for odd [OK]

Common Mistakes:

• Mixing up odd and even conditions
• Misreading the loop range
• Assuming all values are 1 or 0

4. Identify the error in the following embedded C code snippet intended to sample a digital signal into a buffer:

int buffer[5];
for(int i = 0; i <= 5; i++) {
    buffer[i] = digitalRead(PIN);
}

medium

A. digitalRead function is not declared

B. The loop variable i should start at 1

C. Buffer size should be 6 instead of 5

D. The loop condition causes buffer overflow

Solution

1. Step 1: Check loop bounds against buffer size

   The buffer has 5 elements indexed 0 to 4. The loop runs i from 0 to 5 inclusive, which means i=5 is out of bounds.

2. Step 2: Identify the consequence of out-of-bounds access

   Accessing buffer[5] causes buffer overflow, which can crash or corrupt memory.

3. Final Answer:

   The loop condition causes buffer overflow -> Option D

4. Quick Check:

   Loop i <= 5 with size 5 causes overflow [OK]

Hint: Loop index must be less than buffer size [OK]

Common Mistakes:

• Using <= instead of < in loop condition
• Ignoring array index limits
• Assuming digitalRead is missing declaration

5. You want to capture a digital signal's state every 10 microseconds for 100 samples using embedded C. Which approach correctly implements this logic analyzer sampling?

hard

A. Use a recursive function calling digitalRead(PIN) without delay

B. Use a while loop without delay and store digitalRead(PIN) continuously

C. Use a for loop with delayMicroseconds(10) and store digitalRead(PIN) in an array

D. Use a for loop with delay(10) and store analogRead(PIN) in an array

Solution

1. Step 1: Understand timing and sampling requirements

   Sampling every 10 microseconds means a precise short delay between reads. delayMicroseconds(10) provides microsecond delay.

2. Step 2: Match code approach to requirements

   Use a for loop with delayMicroseconds(10) and store digitalRead(PIN) in an array uses a for loop for 100 samples, calls delayMicroseconds(10), and stores digitalRead(PIN) which is correct for digital signal sampling.

3. Final Answer:

   Use a for loop with delayMicroseconds(10) and store digitalRead(PIN) in an array -> Option C

4. Quick Check:

   Precise delay + digitalRead + loop = correct sampling [OK]

Hint: Use delayMicroseconds for microsecond timing [OK]

Common Mistakes:

• Using delay() which is milliseconds, not microseconds
• Reading analog instead of digital signals
• Missing delay causing too fast sampling