- Rewrote the instruction decoder as an enum
- Used imperative_rs to auto-generate the bit twiddling logic
- Implemented Display on that enum, for disassembly
- Rewrote CPU::tick
- Now >10x faster
- Disassembly mode is still 5x slower though
- Implemented time-based benchmarking
- (use option -S to set the number of instructions per epoch)
Chip-8 has no ROM, nor memory management.
- It's much easier to just use contiguous memory.
- Then we can return references to slices of that memory
- ~3x speed increase
Screen exists now, uses 24-bit framebuffer
- We have a 1-bit framebuffer
- I chose colors that look good to me
Controller exists as well, has 16 buttons
- Mapped "0 123 456 789 ab cdef" to (QWERTY) "X 123 QWE ASD zC 4RFV"
- Other chip-8 interpreters may use a different layout
- This is good enough for now.
- F1-F9 map to control functions
- F1, F2: Dump CPU registers/screen contents
- F3, F4: Toggle disassembly/pause
- F5: Single-step the CPU, pausing after
- F6, F7: Set/Unset breakpoint
- F8, F9: Soft/Hard Reset CPU
Created outline of emulator:
The emulator has a Bus, which attaches a CPU to some Memory (Mapped Devices)
The design isn't particularly efficient, but the interpreter only needs to
run at ~500Hz or so. It's Rust. It can do that.
Instructions yet to be implemented:
Cxbb: "Store a random number, masked by bitmask bb, into vX"
Dxyn: "Draw an 8 by n sprite to the screen at coordinates (x, y)"
Fx0A: "Wait for a key, then set vX to the value of the pressed key"
Fx33: "BCD convert X, storing the results in &I[0..3]"
Thoughts going forward:
- It's probably a good idea to parse instructions out into an enum.
I had this in an earlier design, but it didn't really look that good.
However, I haven't read many other emulators before, so I don't know the
style people generally go for.
- I haven't used a native graphics library before, and my cg class was done
entirely in a web browser. That kinda sucks, honestly. Sure the skill
might transfer well, but, >JS
