#include <LiquidCrystal.h>
#include <util/atomic.h> // For atomic ADC reads

// Pins: RS, EN, D4, D5, D6, D7
LiquidCrystal lcd(12, 11, 10, 9, 8, 7);

// Global variables (faster access)
volatile int adcFmax = 0, adcRmax = 0;
char lcdBuf[2][16] = {"Vf: 0.00", "Vr: 0.00"}; // Pre-formatted

void setup() {
  Serial.begin(9600);
  // Ultra-fast LCD init (4-bit mode)
  lcd.begin(16, 2);
  
  // Pre-write static labels
  lcd.print(lcdBuf[0]);
  lcd.setCursor(0, 1);
  lcd.print(lcdBuf[1]);
  
  // Turbo-charge GPIO (AVR only)
  #ifdef __AVR__
  DDRB |= 0b00011111; // Pins 8-12 as output (D8-D12)
  DDRD |= 0b11100000; // Pins 5-7 as output (D5-D7)
  #endif
}

void fastPrint(int row, int value) {
  // Atomic update to prevent screen tearing
  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
    lcd.setCursor(3, row);
    lcd.print(value / 100);   // Whole number
    lcd.write('.');
    lcd.print((value / 10) % 10); // Tenths
    lcd.print(value % 10);    // Hundredths
  }
}

void loop() {
  unsigned long start = micros();
  
  // 1. Blazing-fast ADC reads (6 samples)
  adcFmax = 0; adcRmax = 0;
  for (byte i = 0; i < 15; i++) {
    adcFmax = max(analogRead(A0), adcFmax);
    adcRmax = max(analogRead(A1), adcRmax);
    // Minimal delay for ADC settling
    __asm__ __volatile__ ("nop\n\t" "nop\n\t" "nop\n\t");
  }
  
  // 2. Voltage conversion (integer math)
  int voltageFx100 = (adcFmax * 500 + 512) >> 10; // (x*500)/1024 optimized
  int voltageRx100 = (adcRmax * 500 + 512) >> 10;

  // 3. Update LCD (only if changed)
  static int lastVals[2] = {0,0};
  if (abs(voltageFx100 - lastVals[0]) > 1) {
    fastPrint(0, voltageFx100);
    lastVals[0] = voltageFx100;
  }
  if (abs(voltageRx100 - lastVals[1]) > 1) {
    fastPrint(1, voltageRx100);
    lastVals[1] = voltageRx100;
  }

  // Debug (disable for final deployment)
  Serial.print("Update time (µs): ");
  Serial.println(micros() - start);
  
  delay(50); // 20Hz refresh (adjust as needed)
}