Search found 9 matches

by Concurser
Thu Sep 24, 2020 2:32 pm
Forum: NESemdev
Topic: Help on indirect indexed implementation
Replies: 1
Views: 2534

Help on indirect indexed implementation

Hi, I am continuing my java emu but I have been struggling with the indirect indexed (Y) implementation. It is a conceptual emu, I am not trying to do much more than emulating some NROM games and not being cycle accurate. The code below works on nestest with the following words (MSB) on memory: [3][...
by Concurser
Thu Aug 20, 2020 11:54 am
Forum: NESemdev
Topic: Issue on Indirect,X addressing mode on nestest
Replies: 5
Views: 3083

Re: Issue on Indirect,X addressing mode on nestest

Thanks a lot, just discored that I had an unimplemented opcode: STA (ind,X) (81). Created a small trap to abort my emu execution when this happens. Implied and Immediate opcodes are done here. I entered the phase on Nestest where there is a lot of RAM writes and usually it is hard to verify issues o...
by Concurser
Thu Aug 20, 2020 9:08 am
Forum: NESemdev
Topic: Issue on Indirect,X addressing mode on nestest
Replies: 5
Views: 3083

Re: Issue on Indirect,X addressing mode on nestest

Thanks, a few opcodes later I sorted out another trick on 0-page page wrap when dealing with the LDA ($FF,X) situation. Now I found something interesting that is a possible LDA absolute bug that I can´t figure out the root issue. Please check below, Accumulator is loaded with contents from absolute ...
by Concurser
Wed Aug 19, 2020 2:02 pm
Forum: NESemdev
Topic: Issue on Indirect,X addressing mode on nestest
Replies: 5
Views: 3083

Issue on Indirect,X addressing mode on nestest

Hello folks, could someone give a look? I guess the ram values may be wrong or my (indirect,x) calculation on CFDB A1 80 - LDA ($80, X) is wrong. I am using nestest rom with a simplified dump log (no PPU etc.) address space contents before instruction: mem[0] = 0x04 mem[1] = 0xff ... mem[511] = 0xA5...
by Concurser
Tue Mar 24, 2020 6:42 am
Forum: NESemdev
Topic: PPU filler/init
Replies: 2
Views: 2292

PPU filler/init

Hi, the code below is the very beggining of Donkey Kong (World). My code is not exiting the BEQ-LDA loop even after the estimated 27399 cycles on Mesen debugger. SEI CLD LDA #$10 STA PpuControl_2000 = $90 (was $10 before 27395) LDX #$FF TXS $C7A8 LDA PpuStatus_2002 = $10 (in the 27391th cycle runnin...
by Concurser
Sun Mar 22, 2020 10:38 pm
Forum: NESemdev
Topic: On reset Stack Pointer status
Replies: 2
Views: 2499

Re: On reset Stack Pointer status

Thanks!
by Concurser
Sat Mar 21, 2020 1:03 am
Forum: NESemdev
Topic: On reset Stack Pointer status
Replies: 2
Views: 2499

On reset Stack Pointer status

Using the debugger provided in Mesen, and trying to compare with my early-coded 6502 simulator, I noticed that even with no initial opcode executed, the first instruction (SEI - Set Interrupt Disable) already shows some preset values: 1) Cycle: 8 - ok I found this number in some docs. 2) Flags: 100 ...
by Concurser
Sat Mar 07, 2020 7:55 am
Forum: NESemdev
Topic: Where does the code starts on PRGROM?
Replies: 5
Views: 3986

Re: Where does the code starts on PRGROM?

So I can understand that even for disasm purposes and not yet coding an emu loop I need to simulate the 6502+NES memory address mapping because some of the PRG ROM data is not actual code but rather information that is relevant for the 6502 boot up, right? I will go after learning these vectors and ...
by Concurser
Fri Mar 06, 2020 1:38 pm
Forum: NESemdev
Topic: Where does the code starts on PRGROM?
Replies: 5
Views: 3986

Where does the code starts on PRGROM?

Hi, I am on my fist steps on a toy emulator. Old dream, using my spare time. Very strict targets: only mapper 0 support, no scrolling, no APU...It is a proof of concept and a personal accompishment. The game chosen was Donkey Kong (World) (Rev A), MD-5 is 40319CAD12C80FC095901EB0182DF838. I know tha...