[POC] Expand MMC3s Addressbus to allow 1MB PRG on real HW

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lidnariq
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Joined: Sun Apr 13, 2008 11:12 am

Re: [POC] Expand MMC3s Addressbus to allow 1MB PRG on real H

Post by lidnariq »

So, the original reason for limiting mapper 4 to strictly 512KiB and smaller PRG was that the hardware for that oversize variant did not exist. Enforcing a hard cap on the size was a way to prevent ROM hackers (because, let's be honest, that was the use case) from depending on hardware that didn't exist.

With both this GreenPAK solution and the discrete logic solution, it's clear that that reason isn't trivially true.

Nonetheless, adding this extra hardware is still mechanically hard and still requires donors. Furthermore, new larger-than-512KiB PROMs only come in surface mount packages, and 5V larger-than-512KiB PROMs are conspicuously more expensive. (~3$/ROM instead of ~$1.6)

Much as when I helped persuade you to invent mapper 28 instead of defining an oversize MMC1 extension, I'd again prefer the creation of a new mapper that better represents the interests of developers looking for MMC3-class hardware than just using an oversize MMC3. IMO, something shaped like Namco's 340 plus MMC3 IRQs would be a better candidate.
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