NES Emulator in Common Lisp (2016)

I think if you've never written any sort of lower level code before it's somewhat more daunting. I did spend a little time trying to get this emulator to run but ran into too many issues and gave up -- it's either a problem with some optimizations no longer being valid and raising type errors by default now (e.g. specifying a type as string does not, like other languages, implicitly mean it's either string or null¹) or something about the sdl2 bindings has changed (it's not the most stable of library binds unfortunately and has some misleading docs/examples out there, and the with- macros are not good and best avoided).

The assembler project I linked on the other hand works, though as you say having multiple asdf files is annoying, and the dollhouse.lisp demo makes an unfortunate choice of setting its *path* to #.*compile-file-pathname* Here's what I did to run it without changing that line (which would be better), translate to your flavor of editor+slime for convenience:

    $ git clone https://github.com/ahefner/asm6502
    $ cd asm6502/
    $ sbcl
    * (asdf-here)
    ; my own function I have in ~/.sbclrc, it is just:
    ;(defun asdf-here ()
    ;  (push (uiop:getcwd) asdf:*central-registry*))
    * (asdf:load-system "ichr")
    T
    * (defpackage :dollhouse-demo)
    #<PACKAGE "DOLLHOUSE-DEMO">
    * (defvar dollhouse-demo::*path* "hacks/")
    DOLLHOUSE-DEMO::*PATH*
    * (load "hacks/dollhouse.lisp")
    ; ...output
    ;
    ;(:NUM-UNIQUE 458) 
    ;Empty space begins at F600
    ;Created "/tmp/dollhouse.nes"
    T
    * ^D
    $ fceux /tmp/dollhouse.nes 

¹Example of SBCL raising a type error:

    (let ((x 3))
      (declare (type integer x))
      x)
    ; -> 3
    
    (let ((x nil))
      (declare (type integer x))
      x)
    ; in: LET ((X NIL))
    ;     (LET ((X NIL))
    ;       (DECLARE (TYPE INTEGER X))
    ;       X)
    ; 
    ; caught WARNING:
    ;   Constant NIL conflicts with its asserted type INTEGER.
    ;   See also:
    ;     The SBCL Manual, Node "Handling of Types"
    ; 
    ; compilation unit finished
    ;   caught 1 WARNING condition
    
    debugger invoked on a SIMPLE-TYPE-ERROR in thread
    #<THREAD tid=9761 "main thread" RUNNING {1001750003}>:
      Value of NIL in
      (LET ((X NIL))
      (DECLARE (TYPE INTEGER X))
      X)
    
      is
        NIL,
      not a
        INTEGER.

That's funny considering one of the comments in the README:

> TODO: Write more idiomatic Lisp

Perhaps it's readable because it's not idiomatic :D

Further testing and basically two kind of err code for the 6 rom I tested, example here:

;(nes:setup-and-emulate "1943.nes") #| The value NIL is not of type 6502-CPU::INSTRUCTION when binding 6502-CPU::INST |#

;(nes:setup-and-emulate "DKJU.nes") #| invalid number of arguments: 6 |#

I test both Rom using fcuex64.exe and both worked. Hence, I guess it is not usable. Sadly as the source code is very readable, unlike well python one.

The 6502 bit is fun, but the NES PPU not so much! I never got past that part, maybe one day ...

Just for fun and learning, after writing a CHIP-8 emulator, what would be a good first emulator for a real device to tackle?

NES or Gameboy are my two main ideas, but I'm curious if there are other suggestions.

Sadly it does not work

NES is a little unusual in this respect because the vast majority of cartridges have "mapper" hardware that must be emulated, and there has been a more-or-less continuous trickle of unlicensed cartridges over the years, some of which have unique mappers. If memory serves you can get to something like 95% compatibility with the few dozen most common mappers, but then there's a pile of oddball mappers that are each used by 1 or 2 games (many of which are just pirate hacks of a licensed game).

Yeah a stale repo isn't bad as long as there aren't outstanding issues to be worked. It is still a bad sign in evolving tooling environments like java c++ or rust, but lisp is pretty stable at this point too...

Thanks! I did that and all is good now