initial program counter increment

6502.cpp

@@ -5,6 +5,8 @@
 int Famicom::emulate6502op()
 {
     // increment program counter for instruction read
+    // may need to post increment, but we'll start with this
+    // http://6502.org/tutorials/6502opcodes.html#PC
     cpu->pc++;
     uint8_t opcode = memory->readmem(cpu->pc);
 

addressingmodes.cpp

@@ -16,9 +16,15 @@
  */
 
  // immediate addressing is passing the value specified in code
+uint8_t immediate(cpustate * cpu, Memory * mem)
+ {
+     cpu->pc++;
+     return mem->readmem(cpu->pc);
+ }
 
 uint8_t indexedindirect(cpustate * cpu, Memory * mem)
 {
+    // todo: what to increment pc by?
     // (Indirect,X) aka (zero page,X)
     uint8_t zpageaddr = mem->readmem(cpu->pc+1);
     uint16_t addr = zpageaddr + cpu->x;
@@ -35,22 +41,26 @@ uint8_t zeropage(cpustate * cpu, Memory * mem)
 
 uint8_t absolute(cpustate * cpu, Memory * mem)
 {
+    cpu->pc+=2;
     // is revlendianbytes() necessary?
     return mem->readmem(revlendianbytes(mem->readmem(cpu->pc + 1), mem->readmem(cpu->pc + 2)));
 }
 
 uint8_t zeropagex(cpustate * cpu, Memory * mem)
 {
+    cpu->pc++;
     return mem->readmem(cpu->pc+1)+cpu->x;
 }
 
 uint8_t zeropagey(cpustate * cpu, Memory * mem)
 {
+    cpu->pc++;
     return mem->readmem(cpu->pc+1)+cpu->y;
 }
 
 uint8_t indirectindexed(cpustate * cpu, Memory * mem)
 {
+    // todo: what to increment pc by?
     // (Indirect),Y aka (zero page),Y
     uint8_t zpageaddr = mem->readmem(cpu->pc+1);
     uint16_t addr = (revlendianbytes(mem->readmem(zpageaddr), mem->readmem(zpageaddr+1))) + cpu->y;
@@ -59,13 +69,15 @@ uint8_t indirectindexed(cpustate * cpu, Memory * mem)
 
 uint8_t absolutey(cpustate * cpu, Memory * mem)
 {
+    cpu->pc+=2;
     uint16_t addr = revlendianbytes(mem->readmem(cpu->pc+1), mem->readmem(cpu->pc+2));
     addr += cpu->y;
     return addr;
 }
 
 uint8_t absolutex(cpustate * cpu, Memory * mem)
 {
+    cpu->pc+=2;
     uint16_t addr = revlendianbytes(mem->readmem(cpu->pc+1), mem->readmem(cpu->pc+2));
     addr += cpu->x;
     return addr;

decoder.cpp

@@ -24,7 +24,7 @@ InstructionDecoder::InstructionDecoder(cpustate * c, Memory * m)
  */
 int InstructionDecoder::decode_and_execute(uint8_t opcode)
 {
-    printf("In decode and execute\n");
+    printf("In decode and execute: op: %x, pc: %x\n", opcode, cpu->pc);
     uint8_t cc = opcode & 0b00000011;           // control code
     uint8_t bbb = opcode & 0b00011100;          // addressing mode
     uint8_t aaa = opcode & 0b11100000;          // operation
@@ -70,6 +70,7 @@ int InstructionDecoder::decode_and_execute(uint8_t opcode)
                     // todo: add addressing functions for immediate and absolute
                     case 0b00000000:
                         // (zero page,X) aka (indirect,X)
+                        data = indexedindirect(cpu, mem);
                         // will these inner breaks break out of the entire nested switch?
                         break;
                     case 0b00001000: // immediate
@@ -131,12 +132,5 @@ int InstructionDecoder::decode_and_execute(uint8_t opcode)
         // case 0b11 only used for illegal opcodes
     }
 
-    // increment the program counter
-    // todo: remove all other program counter increments in code
-    // todo: do not increment counter in case of jump
-    // todo: confirm amount to increment by - http://6502.org/tutorials/6502opcodes.html#PC
-    //
-    //cpu->pc += 2;
-
     return 1;       // replace this with cycles used
 }