# To do

## Research

- [ ] Learn how the C64's PC gets initialized (what is the initial value? how is it set?)
- [ ] Review CHIP-8
    - read about the spec / ISA
    - read these, and add them to the bibliography:
        - Steve Losh: https://stevelosh.com/blog/2016/12/chip8-input/
        - https://tonisagrista.com/blog/2021/chip8-spec/

## Documentation

- [ ] Improve docs for flags register

## Design

- [ ] Add a flag for bank-switching to the ~zero-page
- [ ] Move the initial IP value, to eliminate the gap between it and the keypad pointer
    - see paper notes
- [ ] Consider adding a VIP-style keypad-based machine code monitor
- [ ] reconsider ISA order in light of supercat comment here
    - [Why didn't the 6503 have increment/decrement opcodes for A?](https://retrocomputing.stackexchange.com/questions/13023/why-didnt-the-6502-have-increment-decrement-opcodes-for-a)

### Assembler

### For consideration

- [ ] Subroutine stack
- [ ] [Extended system (secret bonus operations)](2023-08-07--dev-notes.md)

## Programming

- [ ] Write some more complex test programs
    - [ ] Display (hex) numbers
    - [ ] Greater than
    - [ ] Minimal LOGO-ish interpreter for turtle graphics

## Run-scripts

- [ ] Replace with running `./cpu.js` and `./assembler.js` diretly

## Simulator

### Assembler

- [ ] Return pure machine code when printing to stdout (and not in debug mode)
- [ ] Pass asm line thru to cpu to print when debugging
    - asm: create a second array that stores every line with code (nor blank or comment only lines) + its line number
    - cpu: accept an optional debugging array, print line # and statement
- [ ] Validate labels

### CPU

- [ ] Add a mode that prints the display as text, but still animates

- [ ] Make single-stepping work with simulated keypad

- [ ] Allow running pre-compiled machine code

    I'm thinking of an interface like this...

        $ ./cpu.js -mc code.bin  
        $ ./cpu.js code.asm
        $ ./cpu.js --debug code.asm

    Full list of flags I want:

        -d --debug
        -s --singlestep
        -p --prettydisplay
        -mc --machinecode


### Possible under-the-hood improvements

- [ ] Do a proper binary version... (or lose the typed arrays?)
- [ ] Extract debugging to its own module
- [ ] DRY out addition and subtraction