tyra VS ps2sdk

There is also a (relatively) easier method: tyra. Tyra is an engine: it does the hard work talking to the hardware for you. You can follow the various tutorials (if I remember well, they are in C++ language, that is quite similar to C, but I suggesto to read something about it anyway) and maybe in a few hours you will have something running on the Playstation2.

Need an graphics engine? There's tyra

Second: You need an SDK, you can use ps2sdk.

I think the ps2 sdk should have the documentation that you need. As for other discussions, a lot of good information has become hard to find due to the shutdown of a couple forums. Assemblergames and PSX-scene probably had a bunch of useful info. You can still find the stuff, but it has become much harder as the archives don't keep the old site format. There's also the backup of the ps2 linux site that has lots of good info. Then there are the several gaming and modding forums that should still have info. You should be able to find most of this with your search engine of choice.

It’s a thing I’ve looked into! There is an SDK out there. I haven’t used it, but I think it would be interesting to mess around with.

In case you're not familiar, many consoles released in the past 2 decades (especially Nintendo ones) can be modded quite easily to run homebrew (and as a side effect, usually also game backups). Here's a guide for the 3DS, just as an example. These consoles have official SDKs, but homebrew devs usually avoid those for legal reasons - instead, unofficial ones like devKitPro, PS2SDK, PSL1GHT etc. are used.

As to your question... yeah, it's hard. I was recently poking around in the code for the homebrew PS2 SDK. It took probably a few weeks of evenings and weekends to understand the specific area that I was interested in. Some of that was due to PS2-specific details (some code runs on the main processor, some code runs on a subprocessor, and a task might be split between the two). Part of it was due to the code not really having a lot of comments.