Fix buttons by replacing SoftwareSerial with Timer 1 ISR serial TX for screen and removing MUX code

Arduino/LIN_to_IR/LIN_to_IR.cpp

@@ -10,15 +10,42 @@
 #define FAULT_PIN      PIN_PB1 // Digital pin 1
 #define CS_PIN         PIN_PB3 // Digital pin 11
 
-#define RTI_RX_PIN     PIN_PA4 // Digital pin 6 (Unused/LED COM)
 #define RTI_TX_PIN     PIN_PA5 // Digital pin 5
-#define MUX_LOGIC_SEL_PIN PIN_PA6 // Digital pin 4
 
 #define SYN_FIELD 0x55
 #define SWM_ID 0x20
 
 SoftwareSerial LINBusSerial(RX_PIN, TX_PIN);
-SoftwareSerial rtiSerial(RTI_RX_PIN, RTI_TX_PIN);
+
+#if defined(TIM1_COMPA_vect) && !defined(TIMER1_COMPA_vect)
+  #define TIMER1_COMPA_vect TIM1_COMPA_vect
+#endif
+
+volatile uint16_t rti_tx_buffer = 0xFFFF;
+volatile uint8_t rti_tx_bit_count = 0;
+
+ISR(TIMER1_COMPA_vect) {
+  if (rti_tx_bit_count > 0) {
+    uint8_t bit = rti_tx_buffer & 1;
+    if (bit) {
+      digitalWrite(RTI_TX_PIN, HIGH);
+    } else {
+      digitalWrite(RTI_TX_PIN, LOW);
+    }
+    rti_tx_buffer >>= 1;
+    rti_tx_bit_count--;
+  }
+}
+
+void rti_write_byte(uint8_t data) {
+  while (rti_tx_bit_count > 0) {
+    // Wait for the previous byte to finish transmitting
+  }
+  noInterrupts();
+  rti_tx_buffer = 0x200 | (data << 1);
+  rti_tx_bit_count = 10;
+  interrupts();
+}
 
 // RC-6 timing constants
 // 1 time unit (1t) = 444us
@@ -237,9 +264,9 @@ void setup() {
   pinMode(LED_PIN, OUTPUT);
   digitalWrite(LED_PIN, LOW); // LED OFF
 
-  // Mux logic select pin
+  // Configure RTI TX pin
-  pinMode(MUX_LOGIC_SEL_PIN, OUTPUT);
+  pinMode(RTI_TX_PIN, OUTPUT);
-  digitalWrite(MUX_LOGIC_SEL_PIN, HIGH);
+  digitalWrite(RTI_TX_PIN, HIGH); // Serial idle is HIGH
 
   // Enable MCP2004
   pinMode(CS_PIN, OUTPUT);
@@ -249,7 +276,15 @@ void setup() {
   digitalWrite(FAULT_PIN, HIGH);
 
   LINBusSerial.begin(9600);
-  rtiSerial.begin(2400);
+
+  // Initialize Timer 1 for 2400 Hz CTC interrupts
+  TCCR1A = 0;
+  TCCR1B = 0;
+  TCNT1 = 0;
+  OCR1A = 3332;            // 8,000,000 / (1 * 2400) - 1
+  TCCR1B |= (1 << WGM12);  // CTC mode
+  TCCR1B |= (1 << CS10);   // Prescaler 1
+  TIMSK1 |= (1 << OCIE1A); // Enable interrupt
 
   frame = LinFrame();
   last_frame_time = millis();
@@ -314,7 +349,7 @@ void loop() {
       else byte_to_send = 0x83;
     }
     
-    rtiSerial.write(byte_to_send);
+    rti_write_byte(byte_to_send);
     rti_byte_index = (rti_byte_index + 1) % 3;
   }
 }