From c999052eaad8b52dd50cf40bfad0b6ba093a3bd7 Mon Sep 17 00:00:00 2001
From: Maciej Witkowiak <mwitkowiak@gmail.com>
Date: Thu, 24 Oct 2024 23:59:29 +0200
Subject: [PATCH] don't use u8g2 if the display is not connected (i2c address
 0x3c)

---
 SEEED/C64_keyboard/C64_keyboard.ino | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/SEEED/C64_keyboard/C64_keyboard.ino b/SEEED/C64_keyboard/C64_keyboard.ino
index 493241f..3942431 100644
--- a/SEEED/C64_keyboard/C64_keyboard.ino
+++ b/SEEED/C64_keyboard/C64_keyboard.ino
@@ -58,6 +58,8 @@ constexpr const unsigned long inactivePeriodMillis = 5000; // keep the message o
 // 128x32
 // https://github.com/olikraus/u8g2
 
+bool displayPresent = false;
+
 #include <U8g2lib.h>
 
 U8G2_SSD1306_128X32_UNIVISION_1_HW_I2C u8g2(U8G2_R0);
@@ -135,6 +137,7 @@ void keyReleased() {
 //////////////////////////////////////////////////////////////
 
 void displayKeyMap() {
+  if (!displayPresent) { return; }
   u8g2.firstPage();
   do {
    u8g2.setFlipMode(true);
@@ -151,6 +154,7 @@ void displayKeyMap() {
 
 
 void displayKey() {
+  if (!displayPresent) { return; }
   u8g2.firstPage();
   do {
    u8g2.setFlipMode(true);
@@ -167,6 +171,7 @@ void displayKey() {
 
 
 void displayState(const char* s) {
+  if (!displayPresent) { return; }
   u8g2.firstPage();
   do {
    u8g2.setFlipMode(true);
@@ -181,8 +186,16 @@ void displayState(const char* s) {
 void setup() {
   ckey = new C128keyboard();
 
-  u8g2.begin();
   Wire.begin();
+
+  // detect if display is connected
+  Wire.beginTransmission(0x3C);
+  displayPresent = (0 == Wire.endTransmission());
+
+  if (displayPresent) {
+    u8g2.begin();
+  }
+
   usb.Init();
 
   displayState("Hello world!");
@@ -194,7 +207,7 @@ uint32_t lastUSBstate = 0;
 
 void loop() {
   currentMillis = millis();
-  if (currentMillis - lastPressedMillis > inactivePeriodMillis) {
+  if (displayPresent && (currentMillis - lastPressedMillis > inactivePeriodMillis)) {
     // clear screen if there was no activity for inactivePeriodMillis
     u8g2.firstPage();
     do { } while ( u8g2.nextPage() );