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#include "vcpu.h"
#include "mem.h"
#include "screen.h"
// Program Counter (16 bits but only 12 bits used (4096 memory addresses))
unsigned short PC;
// Index register (16 bits but only 12 bits used (4096 memory addresses))
unsigned short I;
// Stack register (16 bits)
unsigned short S;
// General purpose registers (8 bits each)
// Note last one often used as a flag register
unsigned char V[16];
// Delay timer (8 bits)
unsigned char DT;
// Sound timer (8 bits)
unsigned char ST;
// Current VCPU state
VCPU_State State;
void VCPUInit(){
PC=ADDR_ROM;
}
void VCPUFetch(){
MemRead((char *)&(State.opcode),2,PC);
PC+=2;
}
void VCPUDecode(){
State.X=(State.opcode<<4) & 0xF0;
State.Y=(State.opcode<<8) & 0xF0;
State.N=(State.opcode<<12) & 0xF0;
State.NN=(State.opcode<<8) & 0xFF;
State.NNN=(State.opcode<<4) & 0xFFF0;
}
void VCPUExecute(){
switch(State.opcode & 0xF){
case 0x0:
ScreenClear();
break
;;
case 0x1:
PC=State.NNN;
break
;;
case 0x6:
V[State.X]=State.NN;
break
;;
case 0x7:
V[State.X]+=State.NN;
break
;;
case 0xA:
I=State.NNN;
break
;;
}
}
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