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#include "vcpu.h"
#include "mem.h"
#include "screen.h"
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
// Current VCPU state
VCPU_State State;
void VCPUInit(){
State.PC=ADDR_ROM;
State.S=0;
srand(time(NULL));
}
void VCPUFetch(){
unsigned char byte[2];
MemRead(byte,2,State.PC); // Little indian to -1 no +1
State.opcode=byte[0];
State.opcode=State.opcode<<8;
State.opcode=State.opcode | byte[1];
State.PC+=2;
}
void VCPUDecode(){
State.X=(State.opcode>>8) & 0xF;
State.Y=(State.opcode>>4) & 0xF;
State.N=State.opcode & 0xF;
State.NN=State.Y;
State.NN=State.NN<<4;
State.NN=State.NN | State.N;
State.NNN=State.opcode&0x0FFF;
}
void VCPUExecute(){
// VCPUDump();
switch(State.opcode >> 12){
case 0x0: // Clear screen or return from subroutine
if(State.N == 0){ // Clear screen
ScreenClear();
}
else { // Return from subroutine
State.PC=State.stack[State.S];
State.S--;
}
break
;;
case 0x1: // Jump
State.PC=State.NNN;
break
;;
case 0x2: // Call
State.S++;
State.stack[State.S]=State.PC;
State.PC=State.NNN;
break
;;
case 0x3: // SE: VX, byte
if(State.V[State.X]==State.NN)
State.PC+=2;
break;
;;
case 0x4: // SNE: VX, byte
if(State.V[State.X]!=State.NN)
State.PC+=2;
break;
;;
case 0x5: // SE: VX, VY
if(State.V[State.X]==State.V[State.Y])
State.PC+=2;
break;
;;
case 0x6:
State.V[State.X]=State.NN;
break
;;
case 0x7:
State.V[State.X]+=State.NN;
break
;;
case 0x8: // Register operations
switch(State.N){
case 0x1: // VX = VX OR VY
State.V[State.X]=State.V[State.X] | State.V[State.Y];
break;
;;
case 0x2: // VX = VX AND VY
State.V[State.X]=State.V[State.X] & State.V[State.Y];
break;
;;
case 0x3: // VX = VX XOR VY
State.V[State.X]=State.V[State.X] ^ State.V[State.Y];
break;
;;
case 0x4: // VX = VX + VY
if(State.V[State.X] + State.V[State.Y] > 255)
State.V[REG_FLAG]=1;
else
State.V[REG_FLAG]=0;
State.V[State.X]=(State.V[State.X] + State.V[State.Y]) & 0xFF;
break;
;;
case 0x5: // VX = VX - VY
if(State.V[State.X] > State.V[State.Y])
State.V[REG_FLAG]=1;
else
State.V[REG_FLAG]=0;
State.V[State.X]=State.V[State.X] - State.V[State.Y];
break;
;;
case 0x6: // VX = VX SHR 1
if(State.V[State.X] & 0x1 == 1)
State.V[REG_FLAG]=1;
else
State.V[REG_FLAG]=0;
State.V[State.X]=State.V[State.X] >> 1;
break;
;;
case 0x7: // VX = VY - VX
if(State.V[State.X] < State.V[State.Y])
State.V[REG_FLAG]=1;
else
State.V[REG_FLAG]=0;
State.V[State.X]=State.V[State.Y] - State.V[State.X];
break;
;;
case 0xE: // VX = VX SHL 1
if(State.V[State.X] >> 15 == 1)
State.V[REG_FLAG]=1;
else
State.V[REG_FLAG]=0;
State.V[State.X]=State.V[State.X] << 1;
break;
;;
}
break
;;
case 0x9: // SNE: VX, VY
if(State.V[State.X]!=State.V[State.Y])
State.PC+=2;
break;
;;
case 0xA:
State.I=State.NNN;
break
;;
case 0xB:
State.PC=State.V[0]+State.NNN;
break
;;
case 0xC:
unsigned short n = rand() % 255 + 1;
State.V[State.X]=n & State.NN;
break
;;
case 0xD: // Draw a sprite
int X=State.V[State.X]%63;
int Y=State.V[State.Y]%31;
State.V[REG_FLAG]=0; // Set flag to 0
int width,height;
ScreenWH(&width,&height);
for(char row=0;row<State.N;row++){
// Stop if row out of screen
if(Y+row>=height)
break;
char sprite;
MemRead(&sprite,1,State.I+row); // Load sprite
// Draw sprite
for(int shift=0;shift<8;shift++){
// Stop if column is out of screen
if(X+shift >= width)
break;
if(ScreenPixelApply(X+shift,Y+row,(sprite>>(7-shift))&0x1))
State.V[REG_FLAG]=1;
}
}
break;
;;
case 0xE:
// TODO
break;;
case 0xF:
switch(State.NN){
case 0x07: // Get timer
State.V[State.X]=State.DT;
break;
;;
case 0x0A:
// TODO
break;
;;
case 0x15: // Set timer
State.DT=State.V[State.X];
break;
;;
case 0x18: // Set sound timer
State.ST=State.V[State.X];
break;
;;
case 0x1E: // I = I + VX
State.I=State.I+State.V[State.X];
break;
;;
case 0x29:
// TODO
break;
;;
case 0x33:
// TODO
break;
;;
case 0x55:
MemCopy(State.V,0xF,State.I);
break;
;;
case 0x65:
MemRead(State.V,0xF,State.I);
break;
;;
}
break;
;;
}
}
void VCPUDump(){
printf("opcode: 0x%04x\n",State.opcode&0xFFFF);
printf("X: 0x%01x\n",State.X);
printf("Y: 0x%01x\n",State.Y);
printf("N: 0x%01x\n",State.N);
printf("NN: 0x%02x\n",State.NN);
printf("NNN: 0x%03x\n",State.NNN);
}
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