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add opcode_mem() function to return memory address and not pre-peek

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Of course all of these opcodes need to be tested later...
This commit is contained in:
Vineet K 2024-06-09 22:15:21 +05:30
parent c417bf2276
commit 68ecbce235
1 changed files with 55 additions and 15 deletions
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70
cpu.c
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@ -67,7 +67,7 @@ peek16(uint16_t addr)
static void
memwrite(uint16_t addr, uint8_t byte)
{
memory[addr] = b;
memory[addr] = byte;
}
static void
@ -125,6 +125,50 @@ opcode_arg(enum addressing_mode mode)
return val;
}
static uint16_t
opcode_mem(enum addressing_mode mode)
{
uint8_t arg;
uint16_t val;
if (mode != AM_ABS && mode != AM_ABS_X && mode != AM_ABS_Y)
arg = peek(regs.pc++);
else
arg = peek16(regs.pc), regs.pc += 2;
switch (mode) {
case AM_ZP:
val = arg % 256;
break;
case AM_ZP_X:
val = (arg + regs.x) % 256;
break;
case AM_ZP_Y:
val = (arg + regs.y) % 256;
break;
case AM_ABS:
val = arg;
break;
case AM_ABS_X:
val = arg + regs.x;
break;
case AM_ABS_Y:
val = arg + regs.y;
break;
case AM_IND_X:
val = peek((arg + regs.x) % 256) + peek((arg + regs.x + 1) % 256) * 256;
break;
case AM_IND_Y:
val = peek(arg) + peek((arg + 1) % 256) * 256 + regs.y;
break;
default:
fprintf(stderr, "INVALID ADDRESSING MODE\n");
abort();
}
return val;
}
static void
adc(uint8_t arg)
{
@ -313,9 +357,9 @@ cpy(uint8_t arg)
}
static void
dec(uint8_t arg)
dec(uint16_t mem)
{
/* TODO: complete this */
memwrite(mem, peek(mem) - 1);
}
static void
@ -839,19 +883,19 @@ interpret(void)
cycles += 2;
break;
case 0x18:
clc(opcode_arg(AM_ACC));
clc();
cycles += 2;
break;
case 0xd8:
cld(opcode_arg(AM_ACC));
cld();
cycles += 2;
break;
case 0x58:
cli(opcode_arg(AM_ACC));
cli();
cycles += 2;
break;
case 0xb8:
clv(opcode_arg(AM_ACC));
clv();
cycles += 2;
break;
case 0xc9:
@ -914,24 +958,20 @@ interpret(void)
cpy(opcode_arg(AM_ABS));
cycles += 4;
break;
case 0x3a:
dec(opcode_arg(AM_ACC));
cycles += 2;
break;
case 0xc6:
dec(opcode_arg(AM_ZP));
dec(opcode_mem(AM_ZP));
cycles += 5;
break;
case 0xd6:
dec(opcode_arg(AM_ZP_X));
dec(opcode_mem(AM_ZP_X));
cycles += 6;
break;
case 0xce:
dec(opcode_arg(AM_ABS));
dec(opcode_mem(AM_ABS));
cycles += 6;
break;
case 0xde:
dec(opcode_arg(AM_ABS_X));
dec(opcode_mem(AM_ABS_X));
cycles += 7;
break;
case 0xca: