separate display to its own file

CMakeLists.txt

@@ -38,6 +38,7 @@ pico_sdk_init()
 if (TARGET tinyusb_device)
             add_executable(hello_usb
                 hello_usb.cpp
+                display.cpp
                 )
 
     add_subdirectory(pico-ssd1306)

display.cpp

@@ -0,0 +1,86 @@
+#include <ctype.h>
+#include <cstring>
+
+#include "hardware/i2c.h"
+#include "pico-ssd1306/ssd1306.h"
+#include "pico-ssd1306/textRenderer/TextRenderer.h"
+#include "hardware/gpio.h"
+
+#include "display.h"
+#include <new>
+
+
+using namespace pico_ssd1306;
+
+// Implement the methods declared in `display.h`.
+
+// Use in-place storage for the SSD1306 object to avoid heap allocation on
+// constrained embedded systems. The storage is sized using the complete
+// `SSD1306` type (this file includes the concrete header), and the object
+// is constructed with placement-new during `init()` and explicitly destroyed
+// in the destructor.
+namespace {
+    alignas(SSD1306) unsigned char display_storage[sizeof(SSD1306)];
+    bool display_constructed = false;
+}
+DisplayManager::DisplayManager()
+    : display_(nullptr)
+{
+    last_echo_[0] = '\0';
+}
+
+DisplayManager::~DisplayManager() {
+    if (display_constructed && display_) {
+        // Call destructor explicitly since we used placement-new.
+        display_->~SSD1306();
+        display_constructed = false;
+    }
+    display_ = nullptr;
+}
+
+// (No singleton accessor — the DisplayManager is constructed explicitly by callers.)
+
+void DisplayManager::init(uint8_t i2c_addr) {
+    if (display_) return; // already initialized
+
+    // Initialize I2C for the SSD1306 display (common pins: SDA=GPIO4, SCL=GPIO5)
+    i2c_init(i2c0, 400 * 1000);
+    gpio_set_function(4, GPIO_FUNC_I2C);
+    gpio_set_function(5, GPIO_FUNC_I2C);
+    gpio_pull_up(4);
+    gpio_pull_up(5);
+
+    // Construct the display object in pre-allocated storage to avoid heap use.
+    display_ = reinterpret_cast<SSD1306 *>(display_storage);
+    new (display_) SSD1306(i2c0, i2c_addr, Size::W128xH64);
+    display_constructed = true;
+    display_->setOrientation(false);
+    display_->clear();
+    display_->sendBuffer();
+
+    last_echo_[0] = '\0';
+    refresh("> ", nullptr);
+}
+
+void DisplayManager::refresh(const char *current_input, const char *last_echo) {
+    if (!display_) return;
+    display_->clear();
+
+    size_t input_len = current_input ? strlen(current_input) : 0;
+    const unsigned char *input_font = (input_len > LAST_ECHO_VISIBLE_CHARS) ? font_5x8 : font_12x16;
+
+    pico_ssd1306::drawText(display_, input_font, current_input ? current_input : "", 0, 0);
+
+    const char *echo_to_draw = last_echo ? last_echo : (last_echo_[0] ? last_echo_ : "");
+    pico_ssd1306::drawText(display_, font_12x16, echo_to_draw, 0, 20);
+
+    display_->sendBuffer();
+}
+
+void DisplayManager::set_last_echo(const char *text) {
+    if (!text) return;
+    strncpy(last_echo_, text, sizeof(last_echo_) - 1);
+    last_echo_[sizeof(last_echo_) - 1] = '\0';
+}
+
+// No C-compatible wrappers: prefer `DisplayManager::instance()` API directly.

display.h

@@ -0,0 +1,73 @@
+
+/* display.h
+ * Generated from display.cpp — public declarations for the OLED helper
+ */
+
+#ifndef DISPLAY_H
+#define DISPLAY_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+
+// Display API is provided via the C++ `DisplayManager` singleton below.
+
+#ifdef __cplusplus
+// Expose the C++ DisplayManager so callers can use the class API directly.
+//
+// Note: The implementation constructs the `SSD1306` display object in-place
+// using static storage (no heap allocation). Construct a `DisplayManager` in
+// `main()` and pass it by reference to functions that need to update the
+// display. This avoids global singletons and makes ownership explicit.
+//
+// Example:
+//   int main() {
+//     stdio_init_all();
+//     DisplayManager display;
+//     // pass the display I2C address (common values: 0x3C or 0x3D)
+//     display.init(0x3C);
+//     while (true) {
+//       wait_for_usb_connection();
+//       run_echo_session(display);
+//     }
+//   }
+//
+//   void run_echo_session(DisplayManager &display) {
+//     display.refresh("> ", nullptr);
+//     // ...
+//   }
+//
+// Forward-declare the SSD1306 type to avoid pulling the full display header into
+// every translation unit that includes `display.h`.
+namespace pico_ssd1306 { class SSD1306; }
+
+class DisplayManager {
+public:
+	// Initialize the hardware and display.
+	DisplayManager();
+	~DisplayManager();
+	// Initialize the hardware and display. Pass the SSD1306 I2C address (default 0x3C).
+	void init(uint8_t i2c_addr = 0x3C);
+
+	// Refresh the display content. Either pointer may be nullptr.
+	void refresh(const char *current_input, const char *last_echo);
+
+	// Update stored last-echo text used when `last_echo` is not provided to `refresh()`.
+	void set_last_echo(const char *text);
+
+	// Non-copyable
+	DisplayManager(const DisplayManager &) = delete;
+	DisplayManager &operator=(const DisplayManager &) = delete;
+
+	// Implementation details kept small in the header: pointer to the concrete SSD1306
+	// type (defined in `pico-ssd1306/ssd1306.h`).
+	pico_ssd1306::SSD1306 *display_;
+	char last_echo_[64];
+	static const size_t LAST_ECHO_VISIBLE_CHARS = 10;
+};
+#endif
+
+
+
+#endif // DISPLAY_H
+

hello_usb.cpp

@@ -7,55 +7,12 @@
 #include "pico/time.h" // Needed for time_us_64()
 #include <stdio.h>
 #include <ctype.h>
+#include <cstring>
 
-#include "hardware/i2c.h"
+#include "display.h"
-#include "hardware/gpio.h"
-#include "pico-ssd1306/ssd1306.h"
-#include "pico-ssd1306/textRenderer/TextRenderer.h"
-
-using namespace pico_ssd1306;
-
-// Global display pointer so helper functions can update the OLED
-static SSD1306 *g_display = nullptr;
 
 // Holds last echoed line for display
 static char g_last_echo[128] = "";
-// Scrolling state for last echo (marquee)
-static size_t g_last_echo_scroll_index = 0;
-static uint64_t g_last_echo_last_scroll_ms = 0;
-static const uint64_t SCROLL_INTERVAL_MS = 300; // milliseconds between scroll steps
-static const size_t LAST_ECHO_VISIBLE_CHARS = 10; // visible chars for 12x16 font on 128px width
-
-// Refresh OLED with current input (line 0) and last echoed text (line 2)
-static void refresh_display(const char *current_input, const char *last_echo) {
-    if (!g_display) return;
-    g_display->clear();
-
-    // If current input is longer than 10 chars, use smaller font to fit more text
-    size_t input_len = current_input ? strlen(current_input) : 0;
-    const unsigned char *input_font = (input_len > 10) ? font_5x8 : font_12x16;
-
-    // Draw current input using chosen font
-    pico_ssd1306::drawText(g_display, input_font, current_input, 0, 0);
-
-    // Draw last echoed text using the larger font for readability
-    // If the last echo is longer than visible chars, create a scrolling window
-    size_t last_len = last_echo ? strlen(last_echo) : 0;
-    if (last_len > LAST_ECHO_VISIBLE_CHARS) {
-        char window[LAST_ECHO_VISIBLE_CHARS + 1];
-        // copy up to visible chars starting at scroll index, wrapping as needed
-        for (size_t i = 0; i < LAST_ECHO_VISIBLE_CHARS; ++i) {
-            size_t src = (g_last_echo_scroll_index + i) % last_len;
-            window[i] = last_echo[src];
-        }
-        window[LAST_ECHO_VISIBLE_CHARS] = '\0';
-        pico_ssd1306::drawText(g_display, font_12x16, window, 0, 20);
-    } else {
-        pico_ssd1306::drawText(g_display, font_12x16, last_echo, 0, 20);
-    }
-
-    g_display->sendBuffer();
-}
 
 // Define the maximum size for the input string buffer
 #define MAX_INPUT_LEN 64
@@ -65,7 +22,7 @@ static void refresh_display(const char *current_input, const char *last_echo) {
 #define ASCII_BACKSPACE 8
 
 // Helper function to handle the echoing and resetting of the buffer
-void echo_and_reset(char* buffer, int* index_ptr) {
+void echo_and_reset(char* buffer, int* index_ptr, DisplayManager &display) {
     if (*index_ptr > 0) {
         buffer[*index_ptr] = '\0';
         // Print to USB serial (ALL CAPS)
@@ -82,15 +39,13 @@ void echo_and_reset(char* buffer, int* index_ptr) {
             g_last_echo[i] = (char)toupper(buffer[i]);
         }
         g_last_echo[i] = '\0';
-        // reset scrolling state whenever last echo changes
-        g_last_echo_scroll_index = 0;
-        g_last_echo_last_scroll_ms = time_us_64() / 1000;
     }
 
     *index_ptr = 0;
     printf("> ");
     // Update OLED to show cleared input and last echo
-    refresh_display("", g_last_echo);
+    display.set_last_echo(g_last_echo);
+    display.refresh("", g_last_echo);
 }
 
 void wait_for_usb_connection() {
@@ -101,7 +56,7 @@ void wait_for_usb_connection() {
     printf("\nConnection Established! Starting Echo Session...\n");
 }
 
-void run_echo_session() {
+void run_echo_session(DisplayManager &display) {
     char input_buffer[MAX_INPUT_LEN];
     int buffer_index = 0;
     uint64_t last_char_time = time_us_64();
@@ -122,10 +77,10 @@ void run_echo_session() {
                     printf("\b \b");
                     // update display to reflect removed char
                     input_buffer[buffer_index] = '\0';
-                    refresh_display(input_buffer, g_last_echo);
+                    display.refresh(input_buffer, g_last_echo);
                 }
             } else if (input_char == '\r' || input_char == '\n') {
-                echo_and_reset(input_buffer, &buffer_index);
+                echo_and_reset(input_buffer, &buffer_index, display);
                 // after echo_and_reset the display is refreshed inside it
             } else if (buffer_index < (MAX_INPUT_LEN - 1) && isprint(input_char)) {
                 printf("%c", input_char);
@@ -133,28 +88,19 @@ void run_echo_session() {
                 buffer_index++;
                 // update OLED with current input
                 input_buffer[buffer_index] = '\0';
-                refresh_display(input_buffer, g_last_echo);
+                display.refresh(input_buffer, g_last_echo);
             }
         }
 
         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);
+            echo_and_reset(input_buffer, &buffer_index, display);
             last_char_time = time_us_64();
         }
 
         // Advance marquee for last echoed text if needed
         size_t last_len = strlen(g_last_echo);
         uint64_t now_ms = time_us_64() / 1000;
-        if (last_len > LAST_ECHO_VISIBLE_CHARS) {
-            if (now_ms - g_last_echo_last_scroll_ms >= SCROLL_INTERVAL_MS) {
-                g_last_echo_scroll_index = (g_last_echo_scroll_index + 1) % last_len;
-                g_last_echo_last_scroll_ms = now_ms;
-                // refresh display to show new window
-                refresh_display(input_buffer, g_last_echo);
-            }
-        }
-
         sleep_us(100);
     }
 
@@ -163,30 +109,12 @@ void run_echo_session() {
 
 int main() {
     stdio_init_all();
-
+    DisplayManager display;
-    // Initialize I2C for the SSD1306 display (common pins: SDA=GPIO4, SCL=GPIO5)
+    display.init();
-    i2c_init(i2c0, 400 * 1000);
-    gpio_set_function(4, GPIO_FUNC_I2C);
-    gpio_set_function(5, GPIO_FUNC_I2C);
-    gpio_pull_up(4);
-    gpio_pull_up(5);
-
-    // Create display object (address 0x3C is common). Adjust size/address if needed.
-    SSD1306 display(i2c0, 0x3C, Size::W128xH64);
-    // rotate display 180 degrees (flip). setOrientation(1) flips screen orientation
-    display.setOrientation(false);
-    display.clear();
-    display.sendBuffer();
-
-    // set global pointer and show initial prompt using larger font
-    g_display = &display;
-    g_last_echo[0] = '\0';
-    refresh_display("> ", g_last_echo);
-
 
     while (true) {
         wait_for_usb_connection();
-        run_echo_session();
+        run_echo_session(display);
     }
 
     return 0;