Printf redirect to UART in Embedded C - Mini Project: Build & Apply

Printf Redirect to UART

📖 Scenario: You are working on a small embedded system that uses a UART (Universal Asynchronous Receiver/Transmitter) to send messages to a computer. Normally, printf sends output to a console, but your system does not have one. You want to redirect printf output to the UART so you can see messages on your computer.

🎯 Goal: Build a simple program that redirects printf output to the UART by implementing the _write function. This will let you send text messages from your embedded device to a computer through UART.

📋 What You'll Learn

Create a UART transmit function called UART_Transmit that sends a single character.

Create a _write function that printf uses to send characters.

Redirect printf output to UART by calling UART_Transmit inside _write.

Use printf to send a test message through UART.

💡 Why This Matters

🌍 Real World

Embedded systems often lack screens or consoles. Redirecting <code>printf</code> to UART lets developers see debug messages on a computer.

💼 Career

Embedded software engineers frequently redirect standard output to hardware interfaces like UART for debugging and communication.

1

Create UART Transmit Function

Create a function called UART_Transmit that takes a char parameter named ch and sends it. For this example, just write an empty function body to simulate sending.

Embedded C

// Your code here

Need a hint?

This function will send one character over UART. For now, just create the function with an empty body.

2

Add _write Function to Redirect printf

Add a function called _write with parameters int file, char *ptr, and int len. Inside, use a for loop with variable i from 0 to len to call UART_Transmit(ptr[i]) for each character. Return len at the end.

Embedded C

void UART_Transmit(char ch) {
    // Simulate UART transmit by doing nothing
}

// Your code here

Need a hint?

The _write function is called by printf to send characters. Use a loop to send each character through UART_Transmit.

3

Include and Write main Function

Add #include <stdio.h> at the top. Then write a main function that calls printf("Hello UART!\n") and returns 0.

Embedded C

#include 

void UART_Transmit(char ch) {
    // Simulate UART transmit by doing nothing
}

int _write(int file, char *ptr, int len) {
    for (int i = 0; i < len; i++) {
        UART_Transmit(ptr[i]);
    }
    return len;
}

// Your code here

Need a hint?

The main function runs your program. Use printf to send a test message through UART.

4

Print the Test Message

Run the program and observe the output. The program should print Hello UART! through the UART by calling printf("Hello UART!\n").

Embedded C

#include 

void UART_Transmit(char ch) {
    // Simulate UART transmit by doing nothing
}

int _write(int file, char *ptr, int len) {
    for (int i = 0; i < len; i++) {
        UART_Transmit(ptr[i]);
    }
    return len;
}

int main() {
    printf("Hello UART!\n");
    return 0;
}

// Run the program to see the output

Need a hint?

When you run the program, the message Hello UART! should appear on your UART terminal.