kalymos.PsNee/PSNee/BIOS_patching.h

#pragma once



#ifdef BIOS_PATCH

  volatile uint8_t pulseCounter = 0;
  volatile uint8_t patchStep = 0;


  #ifdef INTERRUPT_RISING

    ISR(PIN_AX_INTERRUPT_VECTOR) {

     /* 
      * PHASE 3: Pulse Counting (Inside ISR)
      * The hardware Interrupt Service Routine (ISR) now takes over.
      * It counts the exact number of incoming pulses on PIN_AX until it 
      * matches the PULSE_COUNT value.
      */


      //if (--pulseCounter == 0) {           
      pulseCounter++;                         
      if (pulseCounter == PULSE_COUNT){           // If pulseCounter reaches the value defined by PULSE_COUNT
       /* 
        * PHASE 4: Precision Bit Alignment
        * Once the PULSE_COUNT is reached, a micro-delay (BIT_OFFSET) is applied.
        * This shifts the timing from the clock edge to the exact bit position 
        * within the data stream that needs modification.
        */
        _delay_us(BIT_OFFSET);                            
       /* 
        * PHASE 5: Data Bus Overdrive (The Patch)
        * Briefly forcing PIN_DX to OUTPUT to pull the line and "nullify" the target bit.
        * This effectively overwrites the BIOS data on-the-fly 
        * before reverting the pin to INPUT to release the bus.
        */
        PIN_DX_OUTPUT;
        _delay_us (OVERRIDE);                       
        PIN_DX_INPUT;                      
        PIN_AX_INTERRUPT_DISABLE;          
        pulseCounter = 0;                    
        patchStep = 1;                       // patchStep is set to 1, indicating that the first patch is completed.
      }
    }

    void Bios_Patching(){

     /* 
      * PHASE 1: Signal Stabilization & Alignment
      * Detects the startup state (Cold Boot vs. Reset). 
      * If the line is already HIGH (Cold Boot), we wait for a full LOW-to-HIGH transition 
      * to ensure we are aligned with the start of a clean clock cycle.
      */

      if (PIN_AX_READ != 0) {                // Case: Power-on / Line high (---__-_-_)

        while (PIN_AX_READ != 0);           // Wait for falling edge
        while (PIN_AX_READ == 0);           // Wait for next rising edge to sync
      }
      else {                                // Case: Reset / Line low (_____-_-_)
        while (PIN_AX_READ == 0);           // Wait for the very first rising edge
      }
     /* 
      * PHASE 2: Reaching the Target Memory Window
      * We introduce a strategic delay (BOOT_OFFSET) to skip initial noise.
      * This points the execution to a known idle gap in the 
      * address range calls before the critical data appears.
      * DELAY: |---//-----|
      * AX:    -_-_//-_-_________-_-_-_ 
      */
      _delay_ms(BOOT_OFFSET);         
       // Armed for hardware detection
       //pulseCounter = PULSE_COUNT; 
      PIN_AX_INTERRUPT_RISING;
      PIN_AX_INTERRUPT_ENABLE;              
      while (patchStep != 1);                   // Wait for the first stage of the patch to complete:
PIN_LED_OFF;
    }
  #endif

  #ifdef INTERRUPT_FALLING

    ISR(PIN_AX_INTERRUPT_VECTOR) {

      pulseCounter++;                         
      if (pulseCounter == PULSE_COUNT){          
        _delay_us (BIT_OFFSET);                          
        PIN_DX_OUTPUT;                   
        _delay_us (OVERRIDE);                       
        PIN_DX_INPUT;                      

        PIN_AX_INTERRUPT_DISABLE;          

        pulseCounter = 0;                    
        patchStep = 1;                       
      }
    }

    void Bios_Patching(){

      if (PIN_AX_READ != 0) {
        while (PIN_AX_READ != 0);           
        while (PIN_AX_READ == 0);           
      }
      else {
        while (PIN_AX_READ == 0);          
      }

      _delay_ms(BOOT_OFFSET);        

      PIN_AX_INTERRUPT_FALLING;     
      PIN_AX_INTERRUPT_ENABLE;    

      while (patchStep != 1);                   
    }
  #endif

  #ifdef INTERRUPT_RISING_HIGH_PATCH
    ISR(PIN_AX_INTERRUPT_VECTOR) {
      pulseCounter++;                         
      if (pulseCounter == PULSE_COUNT){          
        _delay_us (BIT_OFFSET);                                         
        PIN_DX_SET;                     
        PIN_DX_OUTPUT;                   
        _delay_us (OVERRIDE);                       
        PIN_DX_CLEAR;                     
        PIN_DX_INPUT;                      
        PIN_AX_INTERRUPT_DISABLE;          
        pulseCounter = 0;                    
        patchStep = 1;                      
      }
    }

    ISR(PIN_AY_INTERRUPT_VECTOR){

      pulseCounter++;                         
      
      if (pulseCounter == PULSE_COUNT_2) {
        _delay_us (BIT_OFFSET_2);                           
        PIN_DX_OUTPUT;                  
        _delay_us (OVERRIDE_2);                      
        PIN_DX_INPUT;                        
        PIN_AY_INTERRUPT_DISABLE;           
        patchStep = 2;                      
      }
    }

    void Bios_Patching(){
      if (PIN_AX_READ != 0) {
        while (PIN_AX_READ != 0);           
        while (PIN_AX_READ == 0);          
      }
      else {
        while (PIN_AX_READ == 0);          
      }

      _delay_ms(BOOT_OFFSET);

      PIN_AX_INTERRUPT_RISING;                     

      PIN_AX_INTERRUPT_ENABLE;              

      while (patchStep != 1);                  

      while (PIN_AY_READ != 0);             

      _delay_ms(FOLLOWUP_OFFSET);  

      PIN_AY_INTERRUPT_RISING;                    
      PIN_AY_INTERRUPT_ENABLE;            
      while (patchStep != 2);                 
    }

  #endif

#endif

/*
 * ======================================================================================
 * FUNCTION    : Bios_Patching()
 * TARGET      : Data Bus (DX) synchronized via Address Bus (AX / AY)
 * 
 * OPERATIONAL LOGIC:
 *    This function intercepts a specific memory transaction by counting clock cycles 
 *    on Address lines (AX/AY) to inject modified data onto the Data line (DX) 
 *    in real-time (On-the-fly patching).
 *
 * KEY PHASES:
 *    1. SYNC (AX): Aligns the CPU with the first valid address cycle after boot/reset 
 *       to establish a deterministic T0 reference point.
 *    2. GATING (BOOT_OFFSET): Skips initial BIOS noise/calls to reach the target 
 *       memory window.
 *    3. ADDRESS COUNTING (ISR AX): Hardware-based pulse counting using ultra-fast 
 *       decrement-to-zero logic to identify the exact target bit location.
 *    4. DATA OVERDRIVE (DX): Momentarily forces DX pin to OUTPUT mode to overwrite 
 *       the original BIOS bit with a custom logic state.
 *    5. SEQUENCING (Optional AY): Transitions to a secondary address line (AY) for 
 *       multi-stage patching or follow-up verification.
 * ======================================================================================
 */

#ifdef BIOS_PATCH_3

// Shared variables between ISR and main loop
volatile uint8_t pulse_counter = 0;
volatile uint8_t patch_done = 0;


// --- MAIN INTERRUPT SERVICE ROUTINE (ADDRESS AX) ---
ISR(PIN_AX_INTERRUPT_VECTOR) {
    if (--pulse_counter == 0) {           
        // --- PHASE 4: Precision Bit Alignment ---
        __builtin_avr_delay_cycles(BIT_OFFSET_CYCLES);

        // --- PHASE 5: Data Bus Overdrive (Patch applied on DX) ---
        #ifdef INTERRUPT_RISING_HIGH_PATCH
            PIN_DX_SET;       // Pre-set HIGH if needed for this variant
        #endif

        PIN_DX_OUTPUT;       // Take control of the data bus
        __builtin_avr_delay_cycles(OVERRIDE_CYCLES);

        #ifdef INTERRUPT_RISING_HIGH_PATCH
            PIN_DX_CLEAR;     // Release HIGH state
        #endif

        PIN_DX_INPUT;        // Immediately release the data bus
        PIN_AX_INTERRUPT_DISABLE;
        PIN_LED_OFF;
        patch_done = 1;      // Signal completion of stage 1
    }
}

// --- SECONDARY ISR (ADDRESS AY, HIGH_PATCH variant) ---
#ifdef INTERRUPT_RISING_HIGH_PATCH
ISR(PIN_AY_INTERRUPT_VECTOR) {
    if (--pulse_counter == 0) {
        delay_cycles(BIT_OFFSET_2_CYCLES);
        PIN_DX_OUTPUT;
        delay_cycles(OVERRIDE_2_CYCLES);
        PIN_DX_INPUT;
        PIN_AY_INTERRUPT_DISABLE;
        patch_done = 2;      // Signal completion of stage 2
    }
}
#endif

// --- BIOS Patching Main Function ---
void Bios_Patching(void) {
    // --- PHASE 1: Signal Stabilization & Alignment (AX) ---
    if (PIN_AX_READ != 0) {        // Case: Power-on, line is high
        while (PIN_AX_READ != 0);  // Wait for falling edge
        while (PIN_AX_READ == 0);  // Wait for next rising edge to sync
    } else {                       // Case: Reset, line is low
        while (PIN_AX_READ == 0);  // Wait for first rising edge
    }

    // --- PHASE 2: Reaching the Target Memory Window ---
   // _delay_ms(BOOT_OFFSET_MS);

    // --- PHASE 2: Reaching the Target Memory Window (Silence Detection) ---
    // Replaces the fixed _delay_ms(BOOT_OFFSET_MS)
    uint8_t current_confirms = 0;
    
    while (current_confirms < CONFIRM_COUNTER_TARGET) {
        // SILENCE_THRESHOLD 5000 is approx 2.5ms @ 16MHz
        uint16_t count = SILENCE_THRESHOLD; 
        
        while (count > 0) {
            if (PIN_AX_READ != 0) { 
                // Activity detected: Reset both counters immediately
                count = SILENCE_THRESHOLD;
                current_confirms = 0;
            } else {
                // No activity: Countdown towards zero
                count--;
            }
        }
        // One block of silence successfully validated
        current_confirms++;
    }


  
PIN_LED_ON;
    // --- Prepare pulse counter and patch status flag ---
    pulse_counter = PULSE_COUNT;
    patch_done = 0;

    // --- Dynamic interrupt configuration ---
    #if defined(INTERRUPT_RISING) || defined(INTERRUPT_RISING_HIGH_PATCH)
        PIN_AX_INTERRUPT_RISING;
    #elif defined(INTERRUPT_FALLING)
        PIN_AX_INTERRUPT_FALLING;
    #endif

    PIN_AX_INTERRUPT_ENABLE;
    while (patch_done != 1);      // Wait until stage 1 is completed

    // --- Optional secondary patch phase for HIGH_PATCH ---
    #ifdef INTERRUPT_RISING_HIGH_PATCH
        while (PIN_AY_READ != 0);          // Ensure AY line is low before arming
        _delay_ms(FOLLOWUP_OFFSET_MS);

        pulse_counter = PULSE_COUNT_2;     // Reload counter for AY pulses
        PIN_AY_INTERRUPT_RISING;
        PIN_AY_INTERRUPT_ENABLE;
        while (patch_done != 2);           // Wait until stage 2 is completed
    #endif
}

#endif