chip-8/src/vcpu.h

#pragma once

#define VCPU_FREQ 600
#define DTST_FREQ 60
#define SCREEN_FREQ 60
#define REG_FLAG 0xF

/**
 * @brief Store the entire VCPU state
 * 
 */
typedef struct VCPU_State {
  /// @brief Program Counter (16 bits but only 12 bits used (4096 memory addresses))
  unsigned short PC;

  /// @brief Index register (16 bits but only 12 bits used (4096 memory addresses))
  unsigned short I;

  /// @brief Stack register (16 bits)
  unsigned short S;
  unsigned short stack[100]; // Emulated stack

  /// @brief General purpose registers (8 bits each)
  unsigned char V[16]; // Note last one often used as a flag register

  /// @brief Delay timer (8 bits)
  unsigned char DT;

  /// @brief Sound timer (8 bits)
  unsigned char ST;

  /// @brief Intruction (opcode + decoded fields)
  unsigned short opcode;
  unsigned char X;
  unsigned char Y;
  unsigned char N;
  unsigned char NN;
  unsigned short NNN;

  /// @brief Keypressed
  int keypressed; // Not 0 if a key was pressed
  unsigned char key;
  
  /// @brief Count VCPU ticks
  int dt_ticks;
  int st_ticks;
  int screen_ticks;
} VCPU_State;

/**
 * @brief Must be called first!
 * 
 */
void VCPUInit();

/**
 * @brief Fetch instruction from memory
 * 
 */
void VCPUFetch();

/**
 * @brief Decode instruction from the last fetch
 * 
 */
void VCPUDecode();

/**
 * @brief Execute decode instruction
 * 
 */
void VCPUExecute();

/**
 * @brief Fetch, decode and execute an instruction
 * 
 */
void VCPUTick();

/**
 * @brief Simple (a bit) binary to BCD convertion
 * 
 * @param x 
 * @param u 
 * @param t 
 * @param h 
 */
void VCPUDoubleDabble(unsigned char x, unsigned char *u, unsigned char *t, unsigned char *h);

/**
 * @brief Dump VCPU state
 * 
 */
void VCPUDump();