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Limit RDRAM initialization to 4 chips when Expansion Pak is marked as unused - #10

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marian-m12l wants to merge 3 commits into
n64brew:previewfrom
marian-m12l:ipl3_limit_rdram
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marian-m12l wants to merge 3 commits into
n64brew:previewfrom
marian-m12l:ipl3_limit_rdram

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This is a copy of PR DragonMinded/libdragon#1009. See the corresponding conversation to see if this is worth merging or not.


This PR is an attempt at addressing issue DragonMinded/libdragon#425.

It limits RDRAM chips discovery/initialization to 4 chips, essentially simulating running on a console with Jumper Pak only.

It currently relies on the Expansion Pak being marked as "unused" (value 0x01) in the Homebrew ROM header (bits 2-3 at offset 0x3f), but I can see how this may not be wanted (this header is informative, after all). As an alternative, the flag to ignore Expansion Pak could be added by n64tool in another unused header field (e.g. reserved field at offset 0x18), or even in the TOC maybe?

I've tested on real hardware (PAL N64) with a dev IPL3 (prod IPL3 signing underway). On ares it seems to always take the warm boot path?

I have yet to test writing/reading past the 4MiB threshold, but I expect it to fail on hardware, but not on ares (as evidenced by the need to limit the warm boot test loop to 4 chips).

I tried to keep the diff concise yet readable. I'm eager to hear your thoughts on this, especially regarding how to handle the iQue as I'm not familiar with its idiosyncrasies.

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