initial example

hello_usb.c

@@ -0,0 +1,135 @@
+/**
+ * Simple USB Serial Echo Program with Timeout, Reconnect, and Backspace Logic.
+ * This program now correctly handles the backspace character by deleting it 
+ * from the buffer and sending the necessary control codes to the terminal 
+ * for visual deletion.
+ */
+
+#include "pico/stdlib.h"
+#include "pico/time.h" // Needed for time_us_64()
+#include <stdio.h>
+#include <ctype.h>
+
+// Define the maximum size for the input string buffer
+#define MAX_INPUT_LEN 64
+// Define the timeout period: 1 second in microseconds
+#define TIMEOUT_US 5000000
+// ASCII code for Backspace (often sent as 0x08)
+#define ASCII_BACKSPACE 8
+
+// Helper function to handle the echoing and resetting of the buffer
+void echo_and_reset(char* buffer, int* index_ptr) {
+    if (*index_ptr > 0) {
+        // Null-terminate the string
+        buffer[*index_ptr] = '\0';
+        
+        // Echo the string back, converting to uppercase
+        printf("\nEchoed (ALL CAPS): ");
+        for (int i = 0; buffer[i] != '\0'; i++) {
+            printf("%c", toupper(buffer[i]));
+        }
+        printf("\n");
+    }
+    
+    // Reset buffer for next line and print a new prompt
+    *index_ptr = 0;
+    printf("> ");
+}
+
+// Function to handle the initial waiting and reconnect waiting
+void wait_for_usb_connection() {
+    printf("Waiting for USB host to connect...\n");
+    // Wait until the USB host (e.g., terminal program) opens the serial port
+    while (!stdio_usb_connected()) {
+        sleep_ms(100);
+    }
+    // Connection established!
+    printf("\nConnection Established! Starting Echo Session...\n");
+}
+
+void run_echo_session() {
+    char input_buffer[MAX_INPUT_LEN];
+    int buffer_index = 0;
+    // Track the time (in microseconds) when the last character was received
+    uint64_t last_char_time = time_us_64();
+    
+    printf("--- Pico USB String Echo Program Started ---\n");
+    printf("Type a sentence (up to %d chars). It will echo on Enter/Timeout.\n", MAX_INPUT_LEN - 2);
+    printf("--------------------------------------------\n");
+    printf("> "); // Prompt for input
+
+    // Inner loop runs ONLY while the USB connection is active
+    while (stdio_usb_connected()) {
+        
+        // Check for incoming character without blocking
+        int c = getchar_timeout_us(0); 
+
+        if (c != PICO_ERROR_TIMEOUT) {
+            
+            // Character received, update the timer
+            last_char_time = time_us_64();
+            char input_char = (char)c;
+
+            // 1. --- BACKSPACE HANDLING ---
+            if (input_char == ASCII_BACKSPACE || input_char == 127) { // 127 is sometimes sent by terminals (DEL key)
+                if (buffer_index > 0) {
+                    // Decrease buffer index (remove the character)
+                    buffer_index--; 
+                    // Send backspace, space, and backspace to erase the character on the terminal:
+                    // \b: move cursor back
+                    // ' ': overwrite with a space
+                    // \b: move cursor back again, ready for the next character
+                    printf("\b \b"); 
+                }
+            // 2. --- End of Input (Newline/CR) ---
+            } else if (input_char == '\r' || input_char == '\n') {
+                echo_and_reset(input_buffer, &buffer_index);
+            
+            // 3. --- Collect regular characters ---
+            } else if (buffer_index < (MAX_INPUT_LEN - 1) && isprint(input_char)) {
+                
+                // Echo character locally so the user sees what they type
+                printf("%c", input_char);
+                
+                // Store character in the buffer
+                input_buffer[buffer_index] = input_char;
+                buffer_index++;
+            }
+            // Ignore non-printable characters and overflowed buffer input
+        }
+        
+        // 4. Timeout Check 
+        if (buffer_index > 0 && (time_us_64() - last_char_time) > TIMEOUT_US) {
+            printf("\n--- Timeout Reached (5.0s silence) ---\n");
+            echo_and_reset(input_buffer, &buffer_index);
+            last_char_time = time_us_64(); // Reset time to prevent immediate re-trigger
+        }
+        
+        // Add a small delay to prevent the loop from consuming too much CPU time
+        sleep_us(100); 
+    }
+
+    // Connection lost or closed by host
+    printf("\nHost disconnected. Ending Echo Session.\n");
+}
+
+
+int main() {
+    // Initialize Standard I/O (stdio) to use the USB backend
+    stdio_init_all();
+    
+    // Outer loop: Allows the program to run continuously and restart the
+    // session after a disconnection.
+    while (true) {
+        
+        // 1. Wait for a connection
+        wait_for_usb_connection();
+
+        // 2. Run the program logic while connected
+        run_echo_session();
+        
+        // Loop repeats, going back to wait_for_usb_connection()
+    }
+
+    // Note: main should not return
+}