Space Invaders

[n00b1]

I'm also making space invaders emulator and still have some problems which prevents playing the game.

At the moment everything looks like it should until to the part where invaders should come to the screen and then the screen wipes black and resets the program. Same thing happens if I insert coins and press start.

I think the shift register works like it should but I don't know why does this happen.

Other thing is that I got bored playing with the space invaders and tried out the balloon bomber and lunar rescue roms also as they should work with the same hardware I think. But I don't get it how can they work if the rom size is bigger than space invaders 8KB < 12KB. Then they try to set the stack pointer to 0x2400 like space invaders. Isn't that rom area? Anyway as result I get messed graphics in the title screen because it is writing over the program area

[ASH-II]

Hello everybody (New here hope you can help )

I am trying to write Space Invaders on a new OS called SpecBas (it uses the ZX Spectrum Basic++ and outputs to Windows,Linux) it's in Alpha stage and I'm helping test it. (It's a bit like AMOS for the AMIGA but for PC's)

Anyway....

so I have managed to enter all the op codes and I am now up to the part where it draws the aliens in attract mode and from what I can understand (and I use that term in the loosest sense) I now need to emulate IN and OUT for the 'bit shifting' ???

and this is where I am stuck.

so in simple (idiot if you like) terms, what is 'bit shifting'?


how does the IN and OUT affect it (so which ones should I be emulating)

and where are the results stored? are the in the rom/ram or are they stored elsewhere (so I need to set up a new variable?)


Thanks for any help you can give me.

P.S. OR AM I TOTALLY WRONG HERE AND WHAT SHOULD I DO TO GET THE ALIENS DRAWING ?

[pradipna]

"what is 'bit shifting'?"

I don't know the 'In' and 'Out' you're talking about (hadn't attempted to make a space invaders emulator ) but bit shifting is really simple. Read the Bit Shift section of this: http://en.wikipedia.org/wiki/Bitwise_operation
In C++ you can use << and >> operators to shift bits.

And really nice screen shots, good luck!

[ASH-II]

Thanks for the link.

yes I understand that bit it's similar to rrc,rlc, etc I am confused which ports I need to emulate (this is the IN and OUT) just enough to get it running.

As you can see it won't show the Aliens , so is there an interrupt that I'm missing like the screen beam at $20c0

[ASH-II]

Update (if anyone is reading this)

so I got the aliens working and fixed loads of bugs (stupid , stupid opcode mistakes....by me)

the aliens not showing was the SBI opcode

and I now have sound

Just one more bug to fix.....when I shoot the saucer the score shows as 'CLE' instead of '150' also the saucer score is not added to the total score....sigh.

[leonardo2204]

Hey guys, I've been looking at my opcodes for a week now but so far I couldn't accomplish anything on my game, it is always freezing on the ReadByte function telling me it has overflown. I'm developing my emulator in C#. I've seen a lot of sources, like the It's a trap, the one from emulator101.com and js8080, I've compared them with my opcodes but no lucky. Could you take a look and point out the error I'm making ? I'm not asking anyone to DO the emulator for me, but simply help and point the errors out !

My CPU class: pastebin.com/FzSXW2Cg

Thank you very much !

[TRS]

Looking at the code provided I have to do some assumptions. I image manager is an array representing the memory which can be max 64K. Using an int as address pointer can cause overflows as an int in C# is 32 bits whereas the addressbus of the 8080 is only 16 bits. Try to change the PC.Value to ushort (that's a 16 bit unsigned int).

Also when returning a value from an array it is good practise to check if the value provided fits in the bounds of the array before returning the value from the array.

Good luck programming!

[leonardo2204]

TRS, thanks for the quick reply ! I'm aware of all this assumptions you made, but I don't think that my problem is related to architecture problems, but with the opcode table. For what I've seen, SI uses only 50 opcodes, but I've implemented almost all of the 8080 op's, 'cause I want to develop a GB emulator in the future (I know its Z80 ). Anyway, thanks for pointing that out but do you have any ideas ?

Thanks dude !

[TRS]

Try running in debug mode. When the overflow occurs, check all relevant variables values and see if they are still within bounds. Then try to find out why the variable went out of bounds.