chip8-test-rom VS Octo

i ran the test rom https://github.com/corax89/chip8-test-rom/ and it said all opcodes are good except for 8XY1 - 8XY5.

So I've been on the fringes of understanding and writing an emulator for a while and decided to take the plunge with a CHIP8 emulator since it's well understood and a good starting point. I'm writing in C# and I've implemented most things to get it working however when I run This test ROM my output seems to stop at AX. I've tried debugging but I can't really see anything wrong with the code so I'm wondering if anyone has seen this issue before and might know what would cause this in general terms.

I was able to get the IBM Logo working(although the position of the logo is not consistent) but when I try to run this test rom, I get a flickering sprite and a bunch of 0x0000 Opcodes.

Hi, I am a total newbie in emulator development. I implemented a Chip8 emulator in JavaScript, finished it, with unit tests. However, when I load a test rom from https://github.com/corax89/chip8-test-rom the display looks jumbled instead of what supposed to be (in that README on that repo).

It may help to know that that first one isn't testing what it says it's testing: https://github.com/corax89/chip8-test-rom/pull/9

For anyone looking to write a CHIP-8 emulator, Matt Mikolay's writeup is less ambiguous:

https://github.com/mattmikolay/chip-8/wiki/CHIP%E2%80%908-Te...

If you want to target the original Cosmac VIP behavior, corax89's test ROM is good:

https://github.com/corax89/chip8-test-rom

I probably did them in numerical order, although it might be useful to pick a test ROM (second option) and implement instructions in the order they're used in that ROM.

I have been going through, implementing instruction by instruction and I've been having difficulty with instruction 00EE. When testing it with this test rom and I've been getting an output of this:

It's really hard to track down the issue with just this video. Have you tried the test ROM? https://github.com/corax89/chip8-test-rom

Also, this ROM is very useful to ensure you handle opcodes correctly

1. Octo, a CHIP-8 assembler: https://github.com/JohnEarnest/Octo

P.S. Octojam 10 runs until 12:00 AM PST on November 1st! See the following if you're interested! https://itch.io/jam/octojam-10

In addition to what other posters suggested, it could be a good idea to try assembly languages as a way to manually work with locations in memory. Something like Octo could be fun if you want to try memory manipulation without worrying about real-world complexities like syscalls and memory alignment. If you want something extra challenging, you could always try x86 / amd64 assembly. Some C compilers even support inline assembly if you want to mix C and assembly.

Yes, Octo is the most used tool to create CHIP-8 programs today. John has a little introduction text for writing in its dialect here: https://github.com/JohnEarnest/Octo/blob/gh-pages/docs/BeginnersGuide.md

I also want to thank you all for all the advice you gave to me and others about CHIP8. It was very helpful to read some posts here ! I also used John Earnest's OCTO a lot for debugging.

The octo FAQ touches on this "pre-xoring" technique, and theres a worked example of doing this data preparation in macros. I've also written varioustools that can handle the xoring for you.

In my own system, Octo[0], I encode programs and their metadata in a similar steganographic fashion in GIF files. As others have noted here, both GIF and PNG offer extension mechanisms and ways to embed "comments", but popular image-sharing sites universally re-encode images and discard this data. The advantage of GIF over PNG (for my purposes) is that I store an arbitrary payload in a fixed-looking image by creating additional frames of animation.

In the past, I've also used a different technique- if you simply concatenate a PNG onto a JAR (which is really just a ZIP archive) you end up with a file that acts like a PNG unless you change the extension to JAR, in which case it acts like a Java executable. This works because the PNG header is at the beginning of the file, while the ZIP header is at the end. Nowadays, though, desktop Java is pretty much dead, so it's a less exciting party trick.

[0] https://github.com/JohnEarnest/Octo