ipl3checksum

A Python library to calculate the IPL3 checksum for N64 ROMs.

How to use it?

First you need to install the library, one way of doing it is via pip.

python3 -m pip install -U ipl3checksum

Now you can invoke the library from your script.

romBytes = # A big endian bytes-like object
cickind = ipl3checksum.CICKind.CIC_6102_7101

checksum = ipl3checksum.calculateChecksum(romBytes, cickind)
assert checksum is not None # Not able to compute the checksum, probably because rom was too small

print(f"{checksum[0]:08X}")
print(f"{checksum[1]:08X}")

This library also contains a CIC detector:

cickind = ipl3checksum.detectCIC(romBytes)
print(cickind) # Either a `ipl3checksum.CICKind` or None if was not able to detect the CIC

Where does this come from?

This algorithm comes directly from the IPL3, which each variant is part of the first 0x1000 bytes of the rom of every retail N64 ROM.

There are various implementations floating around on the internet, but for this specific one was reverse-engineered by myself. I made this because I couldn't find a library to calculate this checksum, so I decided to reverse-engineer it myself instead of taking somebody else's work. It also was an interesting learning experience.

Note about licensing

Most of the repository is licensed under the MIT license, but I also made a reference implementation that is part of the public domain (licensed under CC0-1.0), feel free to use it however you prefer (acknowledgment is always appreciated, but not required).

I want to learn more! What is an IPL3? What is CIC?

I'm not really the guy that can answer all your hunger for knowledge, but here are a few links that may be helpful:

• CIC-NUS: https://n64brew.dev/wiki/CIC-NUS
• Initial Program Load 3 (IPL3) https://n64brew.dev/wiki/Initial_Program_Load#IPL3
• List of retail games, containing which CIC they use: https://docs.google.com/spreadsheets/d/1WgZ7DZSzWwYIxwg03yoN9NK_0okuSx9dVL2u5MWPQ60/edit#gid=1247952340
• Research about the CIC 6105: https://github.com/Dragorn421/n64checksum
• Disassembly of all the retail IPL3 binaries: https://github.com/decompals/N64-IPL/blob/main/src/ipl3.s

References

• "IPL3 checksum algorithm" section of the "PIF-NUS" article on n64brew.dev: https://n64brew.dev/wiki/PIF-NUS#IPL3_checksum_algorithm
  • Used for getting the "8-bit IPL3" seed value.
• List of retail games, containing which CIC they use: https://docs.google.com/spreadsheets/d/1WgZ7DZSzWwYIxwg03yoN9NK_0okuSx9dVL2u5MWPQ60/edit#gid=1247952340