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;;;; Processor
;;; Processor function
;;;
;;; Each time the *CPU* is called, it executes one operation, meaning it reads the
;;; next value in *M*, when an opcode, it either executes it, or if the opcode
;;; needs a value, gets ready to read it from the next address and do something
;;;
;;; The implementation uses closures for the internal registers.
(defparameter *CPU* (let ((PC 0) (AC 0) (X 0) (Y 0) (SR 0) (SP 0)) #'(lambda ()
(let ((mval (nth PC *M*)))
(if (eql mval +OP_BRK+)
()
(if (eql mval +OP_ORAxi+)
()))))))
;;; External memory, where the zero page, stack and general purpose memory resides
;;; Another file has to implement it.
(defvar *M*)
;;; Processor opcodes
;;; Ends with a small letter, depending on address mode:
;;; ac | accumulator
;;; a | absolute
;;; ax | absolute, X-indexed
;;; ay | absolute, Y-indexed
;;; d | immediate
;;; | implied
;;; i | indirect
;;; xi | X-indexed, indirect
;;; iy | indirect, Y-indexed
;;; r | relative
;;; z | zeropage
;;; zx | zeropage, X-indexed
;;; zy | zeropage, Y-indexed
(defconstant +OP_BRK+ #x00)
(defconstant +OP_ORAxi+ #x01)
(defconstant +OP_ORAz+ #x05)
(defconstant +OP_ASLz+ #x06)
(defconstant +OP_PHP+ #x08)
(defconstant +OP_ORAd+ #x09)
(defconstant +OP_ASLac+ #x0A)
(defconstant +OP_ORAa+ #x0D)
(defconstant +OP_ASLa+ #x0E)
(defconstant +OP_BPLr+ #x10)
(defconstant +OP_ORAiy+ #x11)
(defconstant +OP_ORAzx+ #x15)
(defconstant +OP_ASLzx+ #x16)
(defconstant +OP_CLC+ #x18)
(defconstant +OP_ORAay+ #x19)
(defconstant +OP_ORAax+ #x1D)
(defconstant +OP_ASLax+ #x1E)
(defconstant +OP_JSRa+ #x20)
(defconstant +OP_ANDxi+ #x21)
(defconstant +OP_BITz+ #x24)
(defconstant +OP_ANDz+ #x25)
(defconstant +OP_ROLz+ #x26)
(defconstant +OP_PLP+ #x28)
(defconstant +OP_ANDd+ #x29)
(defconstant +OP_ROLac+ #x2A)
(defconstant +OP_BITa+ #x2C)
(defconstant +OP_ANDa+ #x2D)
(defconstant +OP_ROLa+ #x2E)
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