Explore page based MMU

[fengb]

We are currently representing memory as fully linear, which makes it fast for reading. However, setRom is a non-negligible amount of logic.

What if we had distinct pages of memory instead?

mem: [8]*[1000]u8,

In this scheme, setRom can be a simple pointer swap and we can still get away with fast lookup. The biggest challenge would be exposing this to the memory debugger.

[fengb]

Coarse memory map (block size = 0x1000):

Start	Name
0x0000	ROM Bank 0
0x1000	ROM Bank 0
0x2000	ROM Bank 0
0x3000	ROM Bank 0
0x4000	ROM Bank [N]
0x5000	ROM Bank [N]
0x6000	ROM Bank [N]
0x7000	ROM Bank [N]
0x8000	VRAM
0x9000	VRAM
0xA000	External RAM Bank [N]
0xB000	External RAM Bank [N]
0xC000	Work RAM
0xD000	Work RAM (Bank [N] CGB)
0xE000	Echo RAM / OAM
0xF000	IO

Disadvantages:

• OAM is awkwardly stuck next to echo RAM
  1. Manual mirror means we can't take advantage of banking
  2. Automatic mirror means we have a bizarre escape for OAM
• Bootloader hangs out separately

[fengb]

Block size = 256:

• + OAM can be split from Echo
• + Bootloader can be separate
• - A lot more updates per bank switch (32 - 64 updates)

Another consideration — storing block number instead of pointers:

• + smaller memory usage
• + easier serialization
• ? how to differentiate between cart and dynamic:
  1. Separate enum(u8) { bootloader, cart, dynamic }
  2. Implicit by largest bit (0 = cart, 1 = dynamic). This takes no additional storage space, but bootloader becomes a manual problem again.