Save States

[rynorris]

Stuff to store

• All CPU registers
• Full contents of PRG RAM
• Full contents of CHR RAM (if present)
• Full contents of SRAM
• All internal state of PPU
• All internal state of APU (could maybe skip this, I have a feeling the APU will probably recover itself)
• State of mapper (will be different per-mapper)

Format

Thinking about going with JSON, with base64 encoded blobs for the memory dumps. Or perhaps a binary format like msgpack?

[rynorris]

By basing the implementation on Serde we should be able to switch out serialization formats at will.

Implementation plan:

• Pull out all the state that needs serializing in each component into it's own struct, which is then embedded in the main object. (e.g. cpu.state, apu.state, etc)
• Annotate all of the state objects with serde's Serializable, Deserializable traits. Since these will be simple objects, we should be able to derive these traits automatically.
• Add methods to each object which serialize/deserialize themselves and recursively their children too.

[rynorris]

Possibly don't even need to store PPU state for a v0. We don't reset it on reset for example and it always recovers itself. The downside being that if you load a save state with the emulator paused, it's not going to render anything until you unpause.

[rynorris]

Changing my mind on the implementation plan. I think I would prefer to keep the serializable state objects totally separate in a separate package, and then just have methods to convert each thing into serializable form. This will make the save state API easier to track and thus easier to avoid breaking changes to the format.