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Hatorijr · February 27th, 2009

well i chose space invaders as my next emulation project and i have a lot of the information i need to get started but after i created my decompiler to check what opcodes are being used in the space invaders rom, i immediately came across an issue.

besides the mirror of the first 4000 bytes of memory, which even than goes up to what, 8000? the jump that i see immediately at the start makes no sense as it jumps clearly very far outside the memory range of the emulator and could not possibly work, so i was wondering if anyone could point me to a possible reason why it'd do this or maybe tell me what i may have done wrong? i know i decoded the op code right.

also here is the first little bit of my decompiled space invaders rom.

Code:

0000 : 00       NOP
0001 : 00       NOP
0002 : 00       NOP
0003 : C3 D4 C3 JMP C3D4
0006 : 00       NOP
0007 : 00       NOP
0008 : F5       PUSH PSW
0009 : C5       PUSH BC
000A : D5       PUSH DE
000B : E5       PUSH HL

i know i read in the rom the right way so not sure why it would get the first part of the decoding right and the rest of it would just not turn out right. also i have a lot of other jumps that also reference memory locations in the range of CXXX as well.

thanks in advance for any help.

EDIT: fixed this bug already but decided to update the post.

Space Invaders - EmuTalk.net this is where i found the documents i am using for my emulator and it has some other nice information for anyone interested.

i would just include the documents but the file size is to big to attach.

Last edited by Hatorijr; March 3rd, 2009 at 21:18..

February 27th, 2009	#1 (permalink)
Hatorijr Emu Author Join Date: Dec 2004 Location: North Carolina Posts: 374	my next emulation project well i chose space invaders as my next emulation project and i have a lot of the information i need to get started but after i created my decompiler to check what opcodes are being used in the space invaders rom, i immediately came across an issue. besides the mirror of the first 4000 bytes of memory, which even than goes up to what, 8000? the jump that i see immediately at the start makes no sense as it jumps clearly very far outside the memory range of the emulator and could not possibly work, so i was wondering if anyone could point me to a possible reason why it'd do this or maybe tell me what i may have done wrong? i know i decoded the op code right. also here is the first little bit of my decompiled space invaders rom. Code: 0000 : 00 NOP 0001 : 00 NOP 0002 : 00 NOP 0003 : C3 D4 C3 JMP C3D4 0006 : 00 NOP 0007 : 00 NOP 0008 : F5 PUSH PSW 0009 : C5 PUSH BC 000A : D5 PUSH DE 000B : E5 PUSH HL i know i read in the rom the right way so not sure why it would get the first part of the decoding right and the rest of it would just not turn out right. also i have a lot of other jumps that also reference memory locations in the range of CXXX as well. thanks in advance for any help. EDIT: fixed this bug already but decided to update the post. Space Invaders - EmuTalk.net this is where i found the documents i am using for my emulator and it has some other nice information for anyone interested. i would just include the documents but the file size is to big to attach. Last edited by Hatorijr; March 3rd, 2009 at 21:18..