Add description for out of bounds MBC ram access #594
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This is based on: - Source code of the SameBoy emulator - Dissassembling Pokemon Pinball which depends on this behavior - Mbc1 schematics - https://www.devrs.com/gb/files/mbc1.gif
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Use "modulo max_ram_size" instead of "and (max_ram_size - 1)"? |
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Perhaps "depends" is not the best way to phrase it, what I actually saw is that Pokemon Pinball sets the ram bank to a non zero value and since it does not have banked ram, all accesses are clipped (according to the formula). |
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What point? I want to try with a 32 KiB cart. |
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It depends on the way you are handling this case, originally I just ignored those out of bounds writes, (and returned 0 on reads) with this way it froze after trying to reload a save from sram (boot up -> save -> restart -> load save -> freeze). |
| On most of the MBC's in case an out of bounds address is accessed (selecting unmapped RAM bank), | ||
| only the mapped bits from the address will be used. |
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Wait--is this talking about address, or bank? I know they are combined to ultimately make a single address passed to the chip; but the entire document is written from the perspective of the GB CPU, since that's the most consistent and generally-useful one, and from that perspective, the bank and address are separate.
This is based on:
Since there are many types of MBC's I added that this is for most of the MBC's