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Top 6 mega-drive Open-Source Projects
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MegaDrivePlusPlus
Universal Region mod, 50/60 Hz switch and In-Game-Reset (IGR) for Sega Mega Drive (AKA Genesis)
I'm working on a game for Amiga (another 68k-based platform) and settled on ZX0 to decompress assets on the fly: https://github.com/einar-saukas/ZX0
I was originally using LZ4, but I switched to ZX0 after learning that it can do in-place decompression, which means I don't have to allocate separate memory for the compressed data. I'm very happy with the compression ratio, and decompression of large assets (~48kb) only takes a few frames on a 7MHz 68000.
Also of note is LZ4W, included in Sega Genesis Dev Kit (and discussed in the comments section of OP's article), a variant of LZ4 that only uses word-aligned operations. That makes it much faster on the 68000, which can struggle to efficiently handle 8-bit data. More info here: https://github.com/Stephane-D/SGDK/blob/master/bin/lz4w.txt
The reality is that the vast majority of these FPGA-based clones don't actually perfectly emulate the logic. They're using the same reverse engineering techniques the traditional emulator developers used and sometimes even the same community documentation. The results are often quite good, but they're making a new implementation that matches the observed behavior of the original system to the best of their abilities.
Now there are some exceptions. Nuked MD FPGA[0] is a recent example of an FPGA recreation that is a fairly direct translation of the original logic using silicon die analysis. In this case, the logic is basically identical, but as you guessed the physical layout is different. Generally speaking, you write FPGA "gateware" in a language like Verilog or VHDL. These don't intrinsically have any information about the physical layout of the logic which is handled by the toolchain instead. As wmf says, this is generally not a problem most of the time. For synchronous logic, either the total propagation delay is small enough for a single cycle or it isn't. The toolchain will estimate this delay and report whether you met timing or not for the configured clockspeed.
Not everything you can do in silicon translates well to FPGAs (both clock edges is also generally not well supported for instance), but for the most part these things are easy enough to work around.
[0] https://github.com/nukeykt/Nuked-MD-FPGA
The cartridge and ROM was done by Catskull Electronics. https://catskullelectronics.com/
NOTE:
The open source projects on this list are ordered by number of github stars.
The number of mentions indicates repo mentiontions in the last 12 Months or
since we started tracking (Dec 2020).
mega-drive related posts
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Honebrew on cartridge
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Cave Story keeps doing this weird thing with save states…
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Indie Genesis Games
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Got Cave Story (NXEngine) working!
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Cave Story - Mega Drive/Genesis v0.8.0
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My son playing the Cave Story MegaDrive/Genesis conversation on the Mega Analogue. Fantastic port!
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[GOG] (Game) Cave Story®'s Secret Santa
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A note from our sponsor - InfluxDB
www.influxdata.com | 17 May 2024
Index
What are some of the best open-source mega-drive projects? This list will help you:
| Project | Stars | |
|---|---|---|
| 1 | SGDK | 1,659 |
| 2 | cave-story-md | 547 |
| 3 | rom-properties | 440 |
| 4 | Nuked-MD-FPGA | 284 |
| 5 | MegaDrivePlusPlus | 114 |
| 6 | ym2020 | 4 |
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