Printf debugging over UART in Embedded C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to send a character over UART using printf.

Embedded C

#include <stdio.h>

int main() {
    char c = 'A';
    printf([1]);
    return 0;
}

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

A"%c", c

B"%d", c

C"%s", c

D"%f", c

Attempts:

3 left

💡 Hint

Common Mistakes

Using %d prints the ASCII code, not the character.

Using %s expects a string, not a character.

Use "%c" to print a single character with printf.

2fill in blank

medium

Complete the code to initialize UART for printf debugging.

Embedded C

void UART_Init() {
    // Set baud rate
    UBRR0 = [1];
    // Enable transmitter
    UCSR0B = (1 << TXEN0);
    // Set frame format: 8 data bits, 1 stop bit
    UCSR0C = (1 << UCSZ01) | (1 << UCSZ00);
}

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

A8

B9600

C16

D103

Attempts:

3 left

💡 Hint

Common Mistakes

Setting UBRR0 directly to baud rate value causes wrong speed.

Confusing baud rate with register value.

UBRR0 value 103 sets baud rate to 9600 for 16MHz clock.

3fill in blank

hard

Fix the error in the UART transmit function to send a character correctly.

Embedded C

void UART_Transmit(char data) {
    while (!(UCSR0A & (1 << [1]))) {
        ; // wait for empty transmit buffer
    }
    UDR0 = data;
}

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

AUDRE0

BTXC0

CRXC0

DRXEN0

Attempts:

3 left

💡 Hint

Common Mistakes

Waiting for RXC0 waits for receive complete, not transmit buffer.

Using TXC0 waits for transmit complete, not buffer empty.

UDRE0 bit indicates the transmit buffer is empty and ready for new data.

4fill in blank

hard

Fill both blanks to print a number in decimal and padded uppercase hex using printf for debugging.

Embedded C

int val = 255;
 printf("val = %d (0x%02[1])\n", val, [2]);

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AX

Bval

Cx

D255

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'x' prints lowercase hex letters.

Passing literal value '255' instead of variable 'val'.

Use 'X' for uppercase padded hex (%02X), and 'val' as the argument.

5fill in blank

hard

Fill all three blanks to create a FILE stream that redirects printf to UART.

Embedded C

[1] uartout = FDEV_SETUP_STREAM(UART_Transmit, NULL, [2]);

int main() {
    [3] = &uartout;
    printf("Debug: UART printf ready!\n");
    return 0;
}

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

Astatic FILE

B_FDEV_SETUP_WRITE

Cstdout

Dstdin

Attempts:

3 left

💡 Hint

Common Mistakes

Using stdin instead of stdout redirects input, not output.

Missing 'static' or wrong type for the stream declaration.

'static FILE' declares the output stream, '_FDEV_SETUP_WRITE' for write-only, 'stdout = &uartout' redirects printf.