based off of a discussion in discord earlier about pokémon rby/gsc glitches: jokes for 4 people
![edited comic:
(3DS virtual console GBC showing Pokemon Gold): "What's your opinion on [invalid opcodes]?"
(Virtual Console logo): "As far as I'm concerned, all [opcodes] are 'valid' [opcodes]."](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:gwfx4qjjq2yhjzrgr5xqcnyz/bafkreiboeq3h2jes5twrjvjkvhdpojwij7q5zuw7dnbj65pmdipa7ko76u)
August 13, 2025 at 10:18 PM
based off of a discussion in discord earlier about pokémon rby/gsc glitches: jokes for 4 people
I discovered that adding new opcodes is sometimes easier if I introduce them through handwritten MiniKt assembly functions, so I can reuse the normal function resolution. The compiler inlines them anyway.
#kotlin
#kotlin
November 30, 2025 at 7:41 PM
I discovered that adding new opcodes is sometimes easier if I introduce them through handwritten MiniKt assembly functions, so I can reuse the normal function resolution. The compiler inlines them anyway.
#kotlin
#kotlin
Disassembling Opcodes with a Font
Disassembling Opcodes with a Font
Hackaday Article
hackaday.com
March 15, 2026 at 5:04 PM
Disassembling Opcodes with a Font
[turtles all the way down voice] just bypass the code and write the optimal opcodes directly
January 22, 2026 at 12:39 AM
[turtles all the way down voice] just bypass the code and write the optimal opcodes directly
SimCity SA-1 now runs 5.93x faster than the original version.
Still not enough for me. I'm rewriting the simulation now with SA-1 native opcodes to get the 10x speed up I promised.
Also Japanese support is work in progress.
Still not enough for me. I'm rewriting the simulation now with SA-1 native opcodes to get the 10x speed up I promised.
Also Japanese support is work in progress.
September 24, 2026 at 7:13 PM
SimCity SA-1 now runs 5.93x faster than the original version.
Still not enough for me. I'm rewriting the simulation now with SA-1 native opcodes to get the 10x speed up I promised.
Also Japanese support is work in progress.
Still not enough for me. I'm rewriting the simulation now with SA-1 native opcodes to get the 10x speed up I promised.
Also Japanese support is work in progress.
The 6502 Opcode Periodic Table
February 23, 2026 at 5:27 PM
The 6502 Opcode Periodic Table
Here are some words what I wrote.
I Accidentally Wrote an Emulator (Part 2) - L Break Into Program, 0:1
In the previous post I mentioned how opcodes are decoded into groups using bitwise operators. Now we’re going to expand upon that to look at how to fetch, decode and execute Z80 opcodes. If you look a...
www.breakintoprogram.co.uk
July 23, 2026 at 11:53 AM
Here are some words what I wrote.
i suspect that words (when used in this way) are more like opcodes than "words," representing various directions on the manifold rather than discrete concepts. i am skeptical of the idea that they are meaningless.
October 18, 2025 at 11:29 PM
i suspect that words (when used in this way) are more like opcodes than "words," representing various directions on the manifold rather than discrete concepts. i am skeptical of the idea that they are meaningless.
My Z80 Opcode Calculator app on Google Play was updated yesterday. Undocumented opcodes are now included. Test away!
#z80 #msx #zxspectrum #amstrad
#z80 #msx #zxspectrum #amstrad
Z80 Opcode Calculator - Apps on Google Play
Get your opcodes and mnemonics on the fly.
play.google.com
February 27, 2026 at 10:21 AM
My Z80 Opcode Calculator app on Google Play was updated yesterday. Undocumented opcodes are now included. Test away!
#z80 #msx #zxspectrum #amstrad
#z80 #msx #zxspectrum #amstrad
_stares_ i do not like that this instruction set has both "reset device" and "device reset" opcodes and they have non-trivially different semantics
February 23, 2026 at 1:25 AM
_stares_ i do not like that this instruction set has both "reset device" and "device reset" opcodes and they have non-trivially different semantics
An update to the opcodes app is now available.
* Z80N opcodes and info
* Missing transputer instructions
Remember to tip your developer!
apps.apple.com/us/app/opcod...
* Z80N opcodes and info
* Missing transputer instructions
Remember to tip your developer!
apps.apple.com/us/app/opcod...
July 28, 2026 at 5:31 PM
An update to the opcodes app is now available.
* Z80N opcodes and info
* Missing transputer instructions
Remember to tip your developer!
apps.apple.com/us/app/opcod...
* Z80N opcodes and info
* Missing transputer instructions
Remember to tip your developer!
apps.apple.com/us/app/opcod...
Love that the legacy of Commodore was illegal opcodes, the unending saga of Amiga IO lawsuits, and a superfund site
May 31, 2025 at 6:12 AM
Love that the legacy of Commodore was illegal opcodes, the unending saga of Amiga IO lawsuits, and a superfund site
This is quite addictive. I’ve already got it running a subset of Z80. It helps that I’ve already written a disassembler, so have worked out how to decode opcodes.
I realised this afternoon that the Z80 disassembler I wrote in C a couple of years ago would be a really good foundation for a Z80 emulator. Yes I know there are a load of them online, but where’s the fun in using someone else’s?
May 15, 2026 at 11:08 AM
This is quite addictive. I’ve already got it running a subset of Z80. It helps that I’ve already written a disassembler, so have worked out how to decode opcodes.
I’d forgotten to add the SP0-256 speech chip to the retro Opcodes app.
But why stop at just adding the chip information?
But why stop at just adding the chip information?
August 23, 2026 at 4:05 AM
I’d forgotten to add the SP0-256 speech chip to the retro Opcodes app.
But why stop at just adding the chip information?
But why stop at just adding the chip information?
Played with hand-generating CPU instruction opcodes in properly compiling my toy language. Here's the code for a function that just negates an int 😅
Though I've realized that opcodes are the easy part! I also need conversion to SSA & register allocation & other stuff...
Though I've realized that opcodes are the easy part! I also need conversion to SSA & register allocation & other stuff...
December 18, 2025 at 8:45 PM
Played with hand-generating CPU instruction opcodes in properly compiling my toy language. Here's the code for a function that just negates an int 😅
Though I've realized that opcodes are the easy part! I also need conversion to SSA & register allocation & other stuff...
Though I've realized that opcodes are the easy part! I also need conversion to SSA & register allocation & other stuff...
Building tiny CPUs in the terminal!🤯
🧬 NanoCore — An 8-bit CPU emulator + assembler + TUI debugger
🔥 Fully minimal 256-byte memory with variable-length opcodes
🦀 Written in Rust & built with @ratatui.rs
⭐ GitHub: github.com/AfaanBilal/N...
#rustlang #ratatui #tui #emulator #asm #terminal
🧬 NanoCore — An 8-bit CPU emulator + assembler + TUI debugger
🔥 Fully minimal 256-byte memory with variable-length opcodes
🦀 Written in Rust & built with @ratatui.rs
⭐ GitHub: github.com/AfaanBilal/N...
#rustlang #ratatui #tui #emulator #asm #terminal
December 8, 2025 at 9:11 AM
Building tiny CPUs in the terminal!🤯
🧬 NanoCore — An 8-bit CPU emulator + assembler + TUI debugger
🔥 Fully minimal 256-byte memory with variable-length opcodes
🦀 Written in Rust & built with @ratatui.rs
⭐ GitHub: github.com/AfaanBilal/N...
#rustlang #ratatui #tui #emulator #asm #terminal
🧬 NanoCore — An 8-bit CPU emulator + assembler + TUI debugger
🔥 Fully minimal 256-byte memory with variable-length opcodes
🦀 Written in Rust & built with @ratatui.rs
⭐ GitHub: github.com/AfaanBilal/N...
#rustlang #ratatui #tui #emulator #asm #terminal
it's messed up that i can just intuitively read codewarrior-flavoured mangled c++ symbols now
this is just like how i spent too long looking at gba disassembly and started being able to recognize thumb opcodes from the raw hex
this is just like how i spent too long looking at gba disassembly and started being able to recognize thumb opcodes from the raw hex
May 31, 2026 at 1:02 AM
it's messed up that i can just intuitively read codewarrior-flavoured mangled c++ symbols now
this is just like how i spent too long looking at gba disassembly and started being able to recognize thumb opcodes from the raw hex
this is just like how i spent too long looking at gba disassembly and started being able to recognize thumb opcodes from the raw hex
Opcodes app got an update. The Quiz was debugged, and a new compact opcodes view added. Huh this screenshot does NOT do it justice. It’s free to download so go get it and see what I mean.
apps.apple.com/us/app/opcod...
apps.apple.com/us/app/opcod...
July 22, 2026 at 4:10 PM
Opcodes app got an update. The Quiz was debugged, and a new compact opcodes view added. Huh this screenshot does NOT do it justice. It’s free to download so go get it and see what I mean.
apps.apple.com/us/app/opcod...
apps.apple.com/us/app/opcod...
different social opcodes
December 11, 2024 at 7:01 PM
different social opcodes
The best thing about it are the illegal opcodes that do the same thing as other opcodes but with weird and sometimes useful side effects
(Now Go Bang!) 6502 “Illegal” Opcodes Demystified
A closer look at the “illegal” opcodes and undocumented instructions of the MOS 6502 MPU.
www.masswerk.at
June 10, 2025 at 1:53 PM
The best thing about it are the illegal opcodes that do the same thing as other opcodes but with weird and sometimes useful side effects
The oldster codes the opcodes directly in binary with a series of switches, and manual advances the execution pointer with a foot pedal.
February 4, 2025 at 10:47 AM
The oldster codes the opcodes directly in binary with a series of switches, and manual advances the execution pointer with a foot pedal.
...storing the prediction IN the opcodes themselves!
If you don’t understand why that’s insane, bear with me for a second.
Imagine your binary has an ordinary if statement, that compiles down to a jump if equal instruction (JE).
If you don’t understand why that’s insane, bear with me for a second.
Imagine your binary has an ordinary if statement, that compiles down to a jump if equal instruction (JE).
June 5, 2026 at 7:22 PM
...storing the prediction IN the opcodes themselves!
If you don’t understand why that’s insane, bear with me for a second.
Imagine your binary has an ordinary if statement, that compiles down to a jump if equal instruction (JE).
If you don’t understand why that’s insane, bear with me for a second.
Imagine your binary has an ordinary if statement, that compiles down to a jump if equal instruction (JE).
puritan AI shuts itself down because x86 includes opcodes that aren't in the Bible
March 2, 2026 at 3:09 PM
puritan AI shuts itself down because x86 includes opcodes that aren't in the Bible
Took a byte off the "petscii maze" effect, down to 13 bytes but unfortunately has a fixed pattern and uses two of the undocumented opcodes.
June 13, 2026 at 12:59 PM
Took a byte off the "petscii maze" effect, down to 13 bytes but unfortunately has a fixed pattern and uses two of the undocumented opcodes.