Chip 8

[overclocked]

Hi,

This is my first post here. It looks like some good chip-8 dudes have posted here so I'm going give my question a chance. I'm a C# programmer as a profession, but fiddles with hardware as a hobby. My last summer vacation project was a hardware chip-8 implemented in a single FPGA. I think it is one of the first of its kind so that's nice. It connects to a VGA-monitor for graphics and a Atari/Amiga-joystick for control.

Things are starting to work out quite nice but I have a timing problem that seems very hard to fix. The games I have tried out this far is:

BLITZ
BLINKY
SPACE INVADERS
MISSILE
TETRIS
HIDDEN

After reading up on timing I first locked the main frequency to approx. 400Hz (400 chip-8 instructions/second) and made the timer decrease every 1/60s. This works for some games but not all. Now I've embedded info for every game to get its own Hz(100-1000Hz) and also a divider to always lock the TimerRegister to approx. 60Hz regardless of main frequency. It still does not work well with for example HIDDEN.

Have somebody seen the same problem with software emulators? Is there somebody who made a table of settings that work well for all/some chip-8 games? Also when trying out different emulators with the game HIDDEN I've seen different behaviors with keyboard control. Should the cursor move one square at a time or move several squares at a time without requiring neutral keyboard value(no key pressed) in between.

Magnus

[Tobiy]

Most Chip-8 games work well with about 14 instructions/timerupdate (840 instructions/second).
The waitkey-instruction reset the key state before waiting so the cursor should move one square at a time.

Tobiy

[overclocked]

Thanks for the tip Tobiy, that was one of the "bugs" still left in the chip-8 core! Because of the way the hardware is connected, I now wait for NO keypress and then wait for the specific keypress on the FX0A-instruction. Seem to work great. Regarding the timing I try 840 inst/sec and it looks and works quite OK with all games I tried this far with the above keyboardfix.

Next up is sound output. Sound register and opcode-implementation already done but actual sound signal left to fix.

Then I will try to add SuperChip opcodes and graphics!

Some other glitches present is that BLITZ have two problems.

1) The original BLITZ always draw the skyscrapers one pixel too long which end up showing at the top of the screen making the plane run directly into these pixels and get "Game Over" right away. I've read some other emulators writers having problems with this one and as I understand it is a bug the the original code, but thanks to the original implementation not having "Sprite y-wrapping" the extra pixels never showed. I now use a fixed version of the ROM instead. Any thoughts about this?

2) Due to the fact that I'm using a static LFSR-register to implement the random instruction CXNN the skyline in BLITZ always start the same way. In my start sequence this means a skyscraper is drawn in the very left pixelrow (x=0). Is this normal? When the plane wraps around the X, the game automatically lower the plane 1 row in Y. This also mean that when trying to bomb the left-most skyscraper the plane now kills itself because the plane is lowered at the same time. How is this supposed to work? Anyone know anything, that would be great!

Thanks!

[overclocked]

Yo, I don't know how many users that actually reads this long thread but I'll keep adding questions..

Does anybody know about a really good and exact Chip-8 emulator implementation? As a step in building the first CHIP-chip-8 (that is the first implementation using logic gates), I though I would try out writing something in assembler myself. To be able to do this I needed a tool chain for Chip-8 assembler. I've chosen the original Chipper assembler and a great Chip-8 emulator written in JAVA and called JChip8BR.

The chosen chip-8 program is a Monitor/HexMemEditor. Its already working as a HexViewer and just some details left before it can be used to Edit HexValues in memory. BUT, the only emulator I've got that actually can run it is my fixed JChip8BR. Anyone got another GOOD one I could try?

Tronix, I tried your genius sctest program on the JChip8BR and found 3 bugs in the opcodes. After fixing those, the program shows "OK", so I think its probably quite OK now. Is the author listening? Great work you've done. I've fixed up some good updates for the emulator that I'm willing to Commit to GoogleHosting if I were to get membership in the project.
Some updates:
1) Done refactoring to seperate disassembly/execution of chip8-instructions. Switched the const int's in Instruction.java for a new enum eInstruction. This enum holds both the opcode-hexcode, the string and the bitmask used to identify it. It also holds the specific opcode-value. The num also includes a static method to convert from int to eInstruction.
2) New generic/configurable methods to format chip8-addresses/values.
3) Switched fonts from monospaced to fixed size which is much better when formatting source code output. Much better and more output in Memory window.
4) Added a Restart/Reset button/method which does a cold boot (loads the last used file from disk again, resets all registers)
5) Added command-line support for a single parameter consisting of a full path to a chip8-binary file. The emulator now initializes (but does not execute) directly when started.
6) Fixed some misspellings in the source code.
7) Added simple handling of Breakpoints, just double-click in the disassembly window to Toggle breakpoint.
8) Now possible to change register values any time, for example when doing debugging/stepping, even the PC (program counter) can be changed.

[xdaniel_FWB]

Dusting off my account here (last post over 4 years ago, heh), here's the next person to have written a Chip-8 interpreter:




- Written in C, using SDL, SDL_ttf and SDL_gfx
- Appears to be compatible with every regular Chip-8 game I've thrown at it

Download (Win32 binary): http://code.google.com/p/ozmav/downl...zunyan8_v1.rar

Usage is simple; if the interpreter is started without any command line arguments, you get a file selection dialog (see screenshot 1) which allows you to open a Chip-8 program. In-game, you can press F11 to have a look at the remaining controls, while pressing F12 shows the about box and ESC exits the program. Here's hoping I didn't forget anything...

I will probably be trying to build the program on Linux, as well as post the source code later

[MicBeaudoin]

Hello,

here is a little update of my old emu(Chiplol), it is now an upgraded version with a pseudo-3d rendering(change with Ctrl+2). I did it with two other people for a school project.

We compiled it for PSP and managed to... play online between a PSP and a PC! So useless lol(but funny)! It worked with the help of a java server, which I don't have anymore unfortunately.

It passes all tests in of SCTEST.
It's programmed in C++(the emu core is totally portable) with Qt for gui, that's why the download is a little bit big(big dlls)
Btw, it's all in french, sorry for this, I didn't translate it yet.
Here is a screenshot:
http://bayimg.com/FaPgMAACg

And the download(windows, about 3MB):http://rghost.net/2740686

[Remote]

Anyone made one of these in Python 3.x?

[ihearpixels]

Nope.

Or Ruby
Or even NASM/MASM based x86 ASM for the insane.......(wait, that gave me a idea....)

[david winter]

Hi there,

I thought I would never come back to my old 1990s MS-DOS Chip-8 emulator but my curiosity went too far. Luckily I picked an old CDROM with my sources. Got a headake to have MS-DOS booting from a floppy as I can't boot on a USB key. But I rapidly got sick of the old MS-DOS command line prompt and quickly wamped the whole thing from the hard drive.

Which brings me two questions for the heck of it...

1) What's the most accurate Windows-based emulator so far ? I'd like to play a few games for the old fun (both CHIP-8 and Schip).
2) If I had to port my sources to Windows for the challenge, what language would you recommend ?

Finally, are the original Cosmac-VIP games online ? I still have the old hex dumps on my CD and could post them here.
So far as I know, only one or two programs used a call to some 1802 machine code.

Any thoughts ? Thanks!

[smcd]

Hi there,

I thought I would never come back to my old 1990s MS-DOS Chip-8 emulator but my curiosity went too far. Luckily I picked an old CDROM with my sources. Got a headake to have MS-DOS booting from a floppy as I can't boot on a USB key. But I rapidly got sick of the old MS-DOS command line prompt and quickly wamped the whole thing from the hard drive.

...

Any thoughts ? Thanks!

thought i'd derail the thread a bit and respond to the emboldened text- if it's because your bios doesn't support usb booting... never fear! i had an old laptop and put Plop boot manager on it and it works fine, albeit with a couple more steps than official bios support http://www.plop.at/en/bootmanager.html