emu_nes

commit 4525490beb4d4aa3c4359060db177c06ff09b3a1
parent 718f89c9c56ea059f114edbdda098408ec3a6e8f
Author: vin <git@vineetk.net>
Date:   Sun, 30 Jun 2024 15:14:38 -0400

fix indirect JMP bug where the high byte does not increment out of page

https://old.reddit.com/r/EmuDev/comments/15plfes/having_an_issue_with_nestest_on_my_6502_emulator/jvyck7k/

With this, it seems that all official opcodes run as nestest expects.
Now, it's the unofficial opcodes that need to be implemented.

Diffstat:
M
cpu.c
 | 
7
++++---

1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/cpu.c b/cpu.c
@@ -196,7 +196,7 @@ opcode_mem(enum addressing_mode mode)
 		val = arg + regs.y;
 		break;
 	case AM_IND:
-		val = peek16(arg);
+		val = peek(arg) | (peek(((arg + 1) & 0xFF) | (arg & 0xFF00)) << 8);
 		break;
 	case AM_IND_X:
 		val = peek((arg + regs.x) % 256) + peek((arg + regs.x + 1) % 256) * 256;
@@ -1308,9 +1308,10 @@ interpret(void)
 		case 0x6c:
 			mode = AM_IND;
 			mem = peek16(regs.pc);
-			deref = peek(mem);
+			deref = peek16(mem);
 			arg = opcode_mem(mode);
-			jmp(deref);
+			deref = arg;
+			jmp(arg);
 			cycles += 6;
 			printf("JMP");
 			break;