Building a proper 6502 vm

APPLEII/addressing.ino

@@ -0,0 +1,54 @@
+// In fastcpu ino
+extern unsigned short PC;
+extern unsigned char X, Y;
+
+// Addressing Modes
+unsigned short inline a_abs() {
+  PC += 2;
+  return read16(PC-2);
+}
+
+unsigned short inline a_absx() {
+  PC += 2;
+  return (read16(PC-2) + (unsigned short)X);
+}
+
+unsigned short inline a_absy() {
+  PC += 2;
+  return (read16(PC-2) + (unsigned short)Y);
+}
+
+unsigned short inline a_imm() {
+  return PC++; 
+}
+
+//ignore page wrap bug
+unsigned short inline a_ind() {
+  PC += 2;
+  return read16(read16(PC-2));
+}
+
+unsigned short inline a_indx() {
+  return read16(((unsigned short)read8(PC++) + (unsigned short)X)&0xFF);
+}
+
+unsigned short inline a_indy() {
+  return read16(((unsigned short)read8(PC++) + (unsigned short)Y)&0xFF);
+}
+
+unsigned short inline a_rel() {
+  unsigned short addr = (unsigned short)read8(PC++);
+  return addr | ((addr&0x80)?0xFF00:0x0000);
+}
+
+unsigned short inline a_zpg() {
+  return (unsigned short)read8(PC++);
+}
+
+unsigned short inline a_zpgx() {
+  return  ((unsigned short)read8(PC++) + (unsigned short)X)&0xFF;
+}
+
+unsigned short inline a_zpgy() {
+  return  ((unsigned short)read8(PC++) + (unsigned short)Y)&0xFF;
+}

APPLEII/cpu.ino

@@ -1,6 +1,6 @@
 // μ6502 - Barebones 6502 Emulator By Damian Peckett
 // dpeckett.com, <damian.peckett@gmail.com>
-
+/*
 // Address Modes
 #define AD_IMP	0x01
 #define AD_A 	0x02
@@ -60,6 +60,10 @@ const unsigned char flags[] PROGMEM = {
   AD_REL, FL_ALL|AD_INDY, UNDF, UNDF, UNDF, FL_ALL|AD_ZPGX, FL_ZN|AD_ZPGX, UNDF, AD_IMP, FL_ALL|AD_ABSY, UNDF, UNDF, UNDF, FL_ALL|AD_ABSX, FL_ZN|AD_ABSX, UNDF
 };
 
+const void *opcode[] PROGMEM = {
+  
+}
+
 // CPU registers
 unsigned short PC;
 unsigned char STP = 0xFD, A = 0x00, X = 0x00, Y = 0x00, SR = SR_FIXED_BITS;
@@ -89,25 +93,6 @@ void setflags() {
   if(opflags&0x40) SR |= ((result^((unsigned short)A))&(result^value16)&0x0080)>>1; 
 }
 
-// Stack functions
-void push16(unsigned short pushval) {
-  write8(STP_BASE + (STP--), (pushval>>8)&0xFF);
-  write8(STP_BASE + (STP--), pushval&0xFF);
-}
-
-void push8(unsigned char pushval) {
-  write8(STP_BASE + (STP--), pushval);
-}
-
-unsigned short pull16() {
-  value16 = read8(STP_BASE + (++STP)) | ((unsigned short)read8(STP_BASE + (++STP))<< 8);
-  return value16;
-}
-
-unsigned char pull8() {
-  return read8(STP_BASE + (++STP));
-}
-
 void run() {
   // Load the reset vector
   PC = read16(0xFFFC);
@@ -171,6 +156,8 @@ void run() {
         break;
       }
 
+
+
       //opcodes
       switch(opcode) {
         //ADC
@@ -525,4 +512,4 @@ void run() {
         break;
       }
     }
-}
+}*/

APPLEII/fastcpu.ino

@@ -0,0 +1,209 @@
+// μ6502 v2.0 - Barebones 6502 Emulator By Damian Peckett
+// dpeckett.com, <damian.peckett@gmail.com>
+
+//Other constants
+#define SR_FIXED_BITS 0x20
+#define SR_CARRY      0x01
+#define SR_ZERO       0x02
+#define SR_INT        0x04
+#define SR_DEC        0x08
+#define SR_BRK        0x10
+#define SR_OVER       0x40
+#define SR_NEG        0x80
+
+//Stack pointer base address
+#define STP_BASE       0x100
+
+// CPU registers
+unsigned short PC;
+unsigned char STP = 0xFD, A = 0x00, X = 0x00, Y = 0x00, SR = SR_FIXED_BITS;
+
+void run() {
+  // Opcode Addresses, Labels As Values
+  static const void* opcodes[] = {
+    &&BRK, &&ORA_INDX, &&UNDF, &&UNDF, &&UNDF, &&ORA_ZPG, &&ASL_ZPG, &&UNDF, &&PHP, &&ORA_IMM, &&ASL_A, &&UNDF, &&UNDF, &&ORA_ABS, &&ASL_ABS, &&UNDF,
+    &&BPL_REL, &&ORA_INDY, &&UNDF, &&UNDF, &&UNDF, &&ORA_ZPGX, &&ASL_ZPGX, &&UNDF, &&CLC, &&ORA_ABSY, &&UNDF, &&UNDF, &&UNDF, &&ORA_ABSX, &&ASL_ABSX, &&UNDF,
+    &&JSR_ABS, &&AND_INDX, &&UNDF, &&UNDF, &&BIT_ZPG, &&AND_ZPG, &&ROL_ZPG, &&UNDF, &&PLP, &&AND_IMM, &&ROL_A, &&UNDF, &&BIT_ABS, &&AND_ABS, &&ROL_ABS, &&UNDF
+  };
+  
+  unsigned char value8, result8;
+  unsigned short value16, result16;
+  unsigned short ptr;
+ 
+  // Load the reset vector
+  PC = read16(0xFFFC);
+  
+  // Begin Execution
+  goto *opcodes[read8(PC++)];
+  
+  // Instruction interpreter
+  BRK:
+    push16(PC+1);
+    push8(SR|SR_BRK);
+    SR |= SR_INT;
+    PC = read16(0xFFFE);
+    goto *opcodes[read8(PC++)];
+  ORA_INDX:
+    A |= read8(a_indx());
+    flagZero(A);
+    flagNegative(A);      
+    goto *opcodes[read8(PC++)];
+  ORA_ZPG:
+    A |= read8(a_zpg());
+    flagZero(A);
+    flagNegative(A);      
+    goto *opcodes[read8(PC++)];
+  ASL_ZPG:
+    ptr = a_zpg();
+    value16 = read8(ptr);
+    result16 = value16<<1;
+    flagZero(result16&0x00FF);
+    flagNegative(result16&0x00FF);
+    flagCarry(result16);
+    write8(ptr, result16&0x00FF);
+    goto *opcodes[read8(PC++)];
+  PHP:
+    push8(SR|SR_BRK);
+    goto *opcodes[read8(PC++)];
+  ORA_IMM:
+    A |= read8(a_imm());
+    flagZero(A);
+    flagNegative(A);      
+    goto *opcodes[read8(PC++)];
+  ASL_A:
+    value16 = A;
+    result16 = value16<<1;
+    flagZero(result16&0x00FF);
+    flagNegative(result16&0x00FF);
+    flagCarry(result16);
+    A = result16&0x00FF;
+    goto *opcodes[read8(PC++)];
+ ORA_ABS:
+    A |= read8(a_abs());
+    flagZero(A);
+    flagNegative(A);      
+    goto *opcodes[read8(PC++)];
+ ASL_ABS:
+    ptr = a_abs();
+    value16 = read8(ptr);
+    result16 = value16<<1;
+    flagZero(result16&0x00FF);
+    flagNegative(result16&0x00FF);
+    flagCarry(result16);
+    write8(ptr, result16&0x00FF);
+    goto *opcodes[read8(PC++)];
+  BPL_REL:
+    if(!(SR&SR_NEG)) PC += a_rel();
+    goto *opcodes[read8(PC++)];
+  ORA_INDY:
+    A |= read8(a_indy());
+    flagZero(A);
+    flagNegative(A);      
+    goto *opcodes[read8(PC++)];
+  ORA_ZPGX:
+    A |= read8(a_zpgx());
+    flagZero(A);
+    flagNegative(A);      
+    goto *opcodes[read8(PC++)];  
+  ASL_ZPGX:
+    ptr = a_zpgx();
+    value16 = read8(ptr);
+    result16 = value16<<1;
+    flagZero(result16&0x00FF);
+    flagNegative(result16&0x00FF);
+    flagCarry(result16);
+    write8(ptr, result16&0x00FF);
+    goto *opcodes[read8(PC++)];
+  CLC:
+    SR &= ~SR_CARRY;
+    goto *opcodes[read8(PC++)];
+  ORA_ABSY:
+    A |= read8(a_absy());
+    flagZero(A);
+    flagNegative(A);      
+    goto *opcodes[read8(PC++)];
+  ORA_ABSX:
+    A |= read8(a_absx());
+    flagZero(A);
+    flagNegative(A);      
+    goto *opcodes[read8(PC++)];
+  ASL_ABSX:
+    ptr = a_absx();
+    value16 = read8(ptr);
+    result16 = value16<<1;
+    flagZero(result16&0x00FF);
+    flagNegative(result16&0x00FF);
+    flagCarry(result16);
+    write8(ptr, result16&0x00FF);
+    goto *opcodes[read8(PC++)];
+  JSR_ABS:
+    push16(PC-1);
+    PC = a_abs();
+    goto *opcodes[read8(PC++)];
+  AND_INDX:
+    A &= read8(a_indx());
+    flagZero(A);
+    flagNegative(A);      
+    goto *opcodes[read8(PC++)];
+  BIT_ZPG:
+    value8 = read8(a_zpg());
+    result8 = A & value8;
+    flagZero(result8);
+    SR = (SR&0x3F) | (value8&0xC0);
+    goto *opcodes[read8(PC++)];
+  AND_ZPG:
+    A &= read8(a_zpg());
+    flagZero(A);
+    flagNegative(A);      
+    goto *opcodes[read8(PC++)];
+  ROL_ZPG:
+    ptr = a_zpg();
+    value16 = read8(ptr);
+    result16 = (value16 << 1) | (SR&SR_CARRY);
+    flagZero(result16&0x00FF);
+    flagNegative(result16&0x00FF);
+    flagCarry(result16);
+    write8(ptr, result16&0x00FF);
+    goto *opcodes[read8(PC++)];
+  PLP:
+    SR = pull8() | SR_FIXED_BITS;
+    goto *opcodes[read8(PC++)];
+  AND_IMM:
+    A &= read8(a_imm());
+    flagZero(A);
+    flagNegative(A);      
+    goto *opcodes[read8(PC++)];
+  ROL_A:
+    value16 = A;
+    result16 = (value16 << 1) | (SR&SR_CARRY);
+    flagZero(result16&0x00FF);
+    flagNegative(result16&0x00FF);
+    flagCarry(result16);
+    A = result16&0x00FF;
+    goto *opcodes[read8(PC++)];
+  BIT_ABS:
+    value8 = read8(a_abs());
+    result8 = A & value8;
+    flagZero(result8);
+    SR = (SR&0x3F) | (value8&0xC0);
+    goto *opcodes[read8(PC++)];
+  AND_ABS:
+    A &= read8(a_abs());
+    flagZero(A);
+    flagNegative(A);      
+    goto *opcodes[read8(PC++)];  
+  ROL_ABS:
+    ptr = a_abs();
+    value16 = read8(ptr);
+    result16 = (value16 << 1) | (SR&SR_CARRY);
+    flagZero(result16&0x00FF);
+    flagNegative(result16&0x00FF);
+    flagCarry(result16);
+    write8(ptr, result16&0x00FF);
+    goto *opcodes[read8(PC++)];
+  
+  // -- Undefined Opcodes
+  UNDF:
+    // Raise an error
+    goto *opcodes[read8(PC++)];
+}

APPLEII/flags.ino

@@ -0,0 +1,16 @@
+void inline flagZero(unsigned char value) {
+  if(!value) SR |= SR_ZERO;
+  else SR &= ~SR_ZERO;
+}
+
+void inline flagNegative(unsigned char value) {
+  if(value&0x80) SR |= SR_NEG;
+  else SR &= ~SR_NEG;
+}
+
+void inline flagCarry(unsigned short value) {
+  if(value&0xFF00) SR |= SR_CARRY;
+  else SR &= ~SR_CARRY;
+}
+
+

APPLEII/memory.ino

@@ -1026,52 +1026,82 @@ const unsigned char rom[] PROGMEM = { //$E000 - FFFF
 };
 
 unsigned char ram[1024];
-// Free memory for storing BASIC programs
-unsigned char basic[512];
 
-unsigned char read8(unsigned short address) {
-  unsigned char page = address>>8;
-  if(page < 0x04) {
+unsigned char inline read8(unsigned short address) {
+  switch(address>>8) {
+  case 0x00: case 0x01: 
+  case 0x02: case 0x03:
     return ram[address];
-  } else if (page >= 0x04 && page < 0x08) {
+  case 0x04: case 0x05:
+  case 0x06: case 0x07:
     return screenRead(address);
-  } else if (page >= 0x08 && page < 0x10) {
-    return basic[address-0x800];
-  } else if (page >= 0xE0) {
+  case 0xC0:
+    return softSwitch(address);
+  case 0xE0: case 0xE1: 
+  case 0xE2: case 0xE3:
+  case 0xE4: case 0xE5:
+  case 0xE6: case 0xE7:
+  case 0xE8: case 0xE9:
+  case 0xEA: case 0xEB:
+  case 0xEC: case 0xED:
+  case 0xEE: case 0xEF:
+  case 0xF0: case 0xF1: 
+  case 0xF2: case 0xF3:
+  case 0xF4: case 0xF5:
+  case 0xF6: case 0xF7:
+  case 0xF8: case 0xF9:
+  case 0xFA: case 0xFB:
+  case 0xFC: case 0xFD:
+  case 0xFE: case 0xFF:
     return pgm_read_byte_near(rom+address-0xE000);
-  } else {
-    // Keyboard Data
-    if(address == 0xC000) return keyboard_read();
-    // Keyboard Strobe
-    if(address == 0xC010) keyboard_strobe();
-    // Speaker toggle
-    if(address == 0xC030) speaker_toggle();
-    return 0;
+  default:
+    return 0xFF;
   }
 }
 
-unsigned short read16(unsigned short address) {
+unsigned short inline read16(unsigned short address) {
   return (unsigned short)read8(address) | (((unsigned short)read8(address+1))<<8);
 }
 
-void write8(unsigned short address, unsigned char value) {
-  unsigned char page = address>>8;
-  if(page < 0x04) {
+void inline write8(unsigned short address, unsigned char value) {
+  switch(address>>8) {
+  case 0x00: case 0x01: 
+  case 0x02: case 0x03:
     ram[address] = value;
-  } else if(page >= 0x04 && page < 0x08) {
+    break;
+  case 0x04: case 0x05:
+  case 0x06: case 0x07:
     screenWrite(address, value);
-  } else if (page >= 0x08 && page < 0x10) {
-    basic[address-0x800] = value;
-  } else {
-    // Keyboard Strobe
-    if(address == 0xC010) keyboard_strobe();
-    // Speaker toggle
-    if(address == 0xC030) speaker_toggle();
+    break;
+  case 0xC0:
+    softSwitch(address);
+    break;
+  default:
+    return;
   }
 }
 
-void write16(unsigned short address, unsigned short value) {
+void inline write16(unsigned short address, unsigned short value) {
    write8(address, value&0x00FF);
    write8(address+1, (value>>8)&0x00FF);
 }
 
+// Stack functions
+void inline push16(unsigned short pushval) {
+  write8(STP_BASE + (STP--), (pushval>>8)&0xFF);
+  write8(STP_BASE + (STP--), pushval&0xFF);
+}
+
+void inline push8(unsigned char pushval) {
+  write8(STP_BASE + (STP--), pushval);
+}
+
+unsigned short inline pull16() {
+  unsigned short value16 = read8(STP_BASE + (++STP)) | ((unsigned short)read8(STP_BASE + (++STP))<< 8);
+  return value16;
+}
+
+unsigned char inline pull8() {
+  return read8(STP_BASE + (++STP));
+}
+

APPLEII/softswitch.ino

@@ -0,0 +1,14 @@
+unsigned char softSwitch(unsigned short address) {
+  switch(address&0x00FF) {
+  case 0x00: // Keyboard Data
+   return keyboard_read();
+  case 0x10: // Keyboard Strobe
+   keyboard_strobe();
+   return 0xFF;
+  case 0x30: // Speaker toggle
+   speaker_toggle();
+   return 0xFF;
+  default:
+   return 0xFF;
+  }
+}