UxROM with 4 MB PRG ROM

UxROM with 4 MB PRG ROM
by zeroone on 2017-04-30 (#194704)

Quote:

Emulator implementations of iNES mapper 2 treat this as a full 8-bit bank select register, without bus conflicts. This allows the mapper to be used for similar boards that are compatible.
To make use of all 8-bits for a 4 MB PRG ROM, an NES 2.0 header must be used (iNES can only effectively go to 2 MB).

Why is iNES limited to 2 MB? If emulators treat the bank select register as a full 8-bit register, how is that affected by the header type?

Re: UxROM with 4 MB PRG ROM
by lidnariq on 2017-04-30 (#194706)

iNES (as opposed to NES2.0) cannot encode a 4 MiB PRG ROM, because 255×16 = 4080 KiB, and UxROM as encapsulated in mapper 2 is only well-defined when a power of two in size.

Re: UxROM with 4 MB PRG ROM
by zeroone on 2017-04-30 (#194708)

lidnariq wrote:

iNES (as opposed to NES2.0) cannot encode a 4 MiB PRG ROM, because 255×16 = 4080 KiB, and UxROM as encapsulated in mapper 2 is only well-defined when a power of two in size.

I forgot about the header size limitation. Thanks.

Re: UxROM with 4 MB PRG ROM
by tepples on 2017-04-30 (#194713)

I'm curious about what would need 32 Mbit on the NES, other than a multicart. That's over five times as big as the largest licensed NES game (Kirby's Adventure, 6 Mbit) and four times as big as the largest licensed Famicom game (Metal Slader Glory, 8 Mbit).

Re: UxROM with 4 MB PRG ROM
by lidnariq on 2017-04-30 (#194714)

The same things that would make a GBC or NGPC game reach 32mbit+.

Re: UxROM with 4 MB PRG ROM
by rainwarrior on 2017-04-30 (#194715)

tepples wrote:

I'm curious about what would need 32 Mbit on the NES, other than a multicart. That's over five times as big as the largest licensed NES game (Kirby's Adventure, 6 Mbit) and four times as big as the largest licensed Famicom game (Metal Slader Glory, 8 Mbit).

This recently made music ROM is 64MB:
http://www.retrousb.com/product_info.php?cPath=36&products_id=143