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#lang br
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;http://www.multigesture.net/articles/how-to-write-an-emulator-chip-8-interpreter/
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; http://devernay.free.fr/hacks/chip8/C8TECH10.HTM
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; http://mattmik.com/files/chip8/mastering/chip8.html
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(define (split-bytes val)
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(cond
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[(zero? val) (list 0)]
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[else
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(define-values (bytes residual)
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(for/fold ([bytes empty][residual val])
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([i (in-naturals)]
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#:break (zero? residual))
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(define m (modulo residual 16))
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(values (cons m bytes) (arithmetic-shift residual -4))))
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bytes]))
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(module+ test
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(require rackunit)
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(check-equal? (split-bytes #x2B45) (list #x2 #xB #x4 #x5))
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(check-equal? (split-bytes #xCD) (list #xC #xD))
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(check-equal? (split-bytes #xA) (list #xA))
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(check-equal? (split-bytes #x0) (list #x0)))
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(define (join-bytes bytes)
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(for/sum ([b (in-list (reverse bytes))]
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[i (in-naturals)])
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(* b (expt 16 i))))
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(module+ test
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(check-equal? #x2B45 (join-bytes (list #x2 #xB #x4 #x5)))
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(check-equal? #xCD (join-bytes (list #xC #xD)))
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(check-equal? #xA (join-bytes (list #xA)))
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(check-equal? #x0 (join-bytes (list #x0))))
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(define-macro (define-memory-vector ID [FIELD LENGTH SIZE] ...)
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(with-pattern
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([(PREFIXED-ID ...) (prefix-id #'ID "-" #'(FIELD ...))]
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[(PREFIXED-ID-REF ...) (suffix-id #'(PREFIXED-ID ...) "-ref")]
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[(PREFIXED-ID-SET! ...) (suffix-id #'(PREFIXED-ID ...) "-set!")]
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[(FIELD-OFFSET ...) (reverse (cdr
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(for/fold ([accum-stxs (list #'0)])
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([len-size-stx (in-list (syntax->list #'((LENGTH SIZE) ...)))])
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(cons (with-pattern
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([accum (car accum-stxs)]
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[(len size) len-size-stx])
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#'(+ (* len size) accum)) accum-stxs))))])
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#'(begin
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(define ID (make-vector (+ (* LENGTH SIZE) ...)))
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(define (PREFIXED-ID-REF idx)
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(unless (< idx LENGTH)
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(raise-argument-error 'PREFIXED-ID-REF (format "index less than field length ~a" LENGTH) idx))
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(join-bytes
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(for/list ([i (in-range SIZE)])
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(vector-ref ID (+ FIELD-OFFSET i idx)))))
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...
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(define (PREFIXED-ID-SET! idx val)
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(unless (< idx LENGTH)
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(raise-argument-error 'PREFIXED-ID-SET! (format "index less than field length ~a" LENGTH) idx))
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(unless (< val (expt 16 SIZE))
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(raise-argument-error 'PREFIXED-ID-SET! (format "value less than field size ~a" (expt 16 SIZE)) val))
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(for ([i (in-range SIZE)]
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[b (in-list (split-bytes val))])
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(vector-set! ID (+ FIELD-OFFSET i idx) b))) ...)))
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(define-memory-vector chip8
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[opcode 1 2] ; two bytes
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[memory 4096 1] ; one byte per
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[V 16 1] ; one byte per
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[I 2 1] ; index register, 0x000 to 0xFFF (1.5 bytes)
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[pc 2 1] ; program counter, 0x000 to 0xFFF (1.5 bytes)
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[gfx (* 64 32) 1] ; pixels
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[delay_timer 1 1]
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[sound_timer 1 1]
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[stack 16 2] ; 2 bytes each
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[sp 1 2] ; stack pointer
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[key 16 1]) ; keys
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;; Set up render system and register input callbacks
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;(setup-graphics chip8)
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;(setup-input chip8)
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;; Initialize the Chip8 system and load the game into the memory
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#;(define (initialize c)
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;; Initialize registers and memory once
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)
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;(initialize chip8)
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;(load-game chip8 "pong")
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#;(define (emulate-cycle c)
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; // Fetch Opcode
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; // Decode Opcode
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; // Execute Opcode
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;
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; // Update timers
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)
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;; Emulation loop
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#;(let loop ()
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;; Emulate one cycle
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(emulate-cycle chip8)
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;; If the draw flag is set, update the screen
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(when (draw-flag? chip8)
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(draw-graphics chip8))
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;; Store key press state (Press and Release)
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(set-keys chip8)
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(loop)) |