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nes-cpu.el
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nes-cpu.el
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;; -*- lexical-binding: t -*-
(eval-when-compile (require 'cl))
(require 'nes-dma)
(require 'nes-instruction)
(require 'nes-interrupt)
(require 'nes-keypad)
(require 'nes-ppu)
(require 'nes-util)
;; https://wiki.nesdev.com/w/index.php/CPU_registers
(defstruct (nes/cpu-register
(:conc-name nes/cpu-register->))
(acc 0)
(idx-x 0)
(idx-y 0)
(pc 0)
(sp #x01fd)
;; status register
(sr-carry nil)
(sr-zero nil)
(sr-interrupt t)
(sr-decimal nil)
(sr-break t)
(sr-reserved t)
(sr-overflow nil)
(sr-negative nil))
(defstruct (nes/cpu-bus
(:conc-name nes/cpu-bus->))
(ram nil)
(prg-rom (lambda (ignored)))
)
(defstruct (nes/cpu
(:conc-name nes/cpu->))
(cycles 0)
(ppu nil)
(dma nil)
(keypad nil)
(bus (make-nes/cpu-bus))
(register (make-nes/cpu-register))
(interrupt nil)
)
(defun nes/cpu--bus-read (c addr)
(let ((b (nes/cpu->bus c))
(ppu (nes/cpu->ppu c)))
(cond
((< addr #x0800) (aref (nes/cpu-bus->ram b) addr))
((< addr #x2000) (nes/cpu--bus-read c (- addr #x0800)))
((< addr #x4000) (nes/ppu-read ppu (+ (mod addr #x0008) #x2000)))
((eq addr #x4016) (nes/keypad-read (nes/cpu->keypad c)))
;; ((eq addr #x4017) (nes/keypad-read (nes/cpu->keypad c))) ;; 2P
((>= addr #x8000) (funcall (nes/cpu-bus->prg-rom b) addr))
(t 0)
)))
(defun nes/cpu--bus-write (c addr data)
(let ((b (nes/cpu->bus c))
(ppu (nes/cpu->ppu c)))
(cond
((< addr #x2000) (aset (nes/cpu-bus->ram b) (% addr #x0800) data))
((< addr #x4000) (nes/ppu-write ppu (+ (% addr #x0008) #x2000) data))
;; ((< addr #x4014) ( ... )) ;; APU
((eq addr #x4014) (nes/dma-request-transfer (nes/cpu->dma c) data))
((eq addr #x4016) (nes/keypad-write (nes/cpu->keypad c) data))
;; ((eq addr #x4017) (nes/keypad-write (nes/cpu->keypad c) data)) ;; 2P
)))
(defun nes/cpu-read (c addr &optional size)
(setq size (or size :byte))
(setq addr (logand addr #xffff))
(if (eq size :word)
(logior
(logand (nes/cpu--bus-read c addr) #xFF)
(logand (lsh (nes/cpu--bus-read c (1+ addr)) 8) #xFF00)
)
(logand (nes/cpu--bus-read c addr) #xFF)))
(defun nes/cpu-write (c addr data)
(nes/cpu--bus-write c addr data))
(defun nes/cpu-push (c data)
(let* ((register (nes/cpu->register c))
(addr (nes/cpu-register->sp register)))
(nes/cpu-write c (logior #x100 (logand addr #x0ff)) data)
(setf (nes/cpu-register->sp register) (1- addr))))
(defun nes/cpu-pull (c)
(let* ((register (nes/cpu->register c))
(addr (1+ (nes/cpu-register->sp register))))
(setf (nes/cpu-register->sp register) addr)
(nes/cpu-read c (logior #x100 (logand addr #x0ff)))))
(defun nes/cpu-push-status-register (c)
(let ((r (nes/cpu->register c)))
(nes/cpu-push c
(logior (lsh (if (nes/cpu-register->sr-negative r) 1 0) 7)
(lsh (if (nes/cpu-register->sr-overflow r) 1 0) 6)
(lsh (if (nes/cpu-register->sr-reserved r) 1 0) 5)
(lsh (if (nes/cpu-register->sr-break r) 1 0) 4)
(lsh (if (nes/cpu-register->sr-decimal r) 1 0) 3)
(lsh (if (nes/cpu-register->sr-interrupt r) 1 0) 2)
(lsh (if (nes/cpu-register->sr-zero r) 1 0) 1)
(lsh (if (nes/cpu-register->sr-carry r) 1 0) 0)))))
(defun nes/cpu-pull-status-register (c)
(let ((data (nes/cpu-pull c))
(r (nes/cpu->register c)))
(setf (nes/cpu-register->sr-negative r) (nes--logbitp 7 data))
(setf (nes/cpu-register->sr-overflow r) (nes--logbitp 6 data))
(setf (nes/cpu-register->sr-reserved r) (nes--logbitp 5 data))
(setf (nes/cpu-register->sr-break r) (nes--logbitp 4 data))
(setf (nes/cpu-register->sr-decimal r) (nes--logbitp 3 data))
(setf (nes/cpu-register->sr-interrupt r) (nes--logbitp 2 data))
(setf (nes/cpu-register->sr-zero r) (nes--logbitp 1 data))
(setf (nes/cpu-register->sr-carry r) (nes--logbitp 0 data))))
(defun nes/cpu-reset (c)
(let ((r (nes/cpu->register c)))
(setf (nes/cpu-register->sp r) #xfd)
(setf (nes/cpu-register->pc r) (nes/cpu-read c #xfffc :word))
(setf (nes/cpu-register->sr-carry r) nil)
(setf (nes/cpu-register->sr-zero r) nil)
(setf (nes/cpu-register->sr-interrupt r) t)
(setf (nes/cpu-register->sr-decimal r) nil)
(setf (nes/cpu-register->sr-break r) t)
(setf (nes/cpu-register->sr-reserved r) t)
(setf (nes/cpu-register->sr-overflow r) nil)
(setf (nes/cpu-register->sr-negative r) nil)
))
(defun nes/cpu-nmi (c)
(let ((register (nes/cpu->register c)))
(nes/interrupt-deassert-nmi (nes/cpu->interrupt c))
(setf (nes/cpu-register->sr-break register) nil)
(nes/cpu-push c (logand #xFF (lsh (nes/cpu-register->pc register) -8)))
(nes/cpu-push c (logand #xFF (nes/cpu-register->pc register)))
(nes/cpu-push-status-register c)
(setf (nes/cpu-register->sr-interrupt register) t)
(setf (nes/cpu-register->pc register) (nes/cpu-read c #xFFFA :word))))
(defun nes/cpu-irq (c)
(let ((register (nes/cpu->register c)))
(nes/cpu-push c (logand #xff (lsh (nes/cpu-register->pc register) -8)))
(nes/cpu-push c (logand #xff (nes/cpu-register->pc register)))
(nes/cpu-push-status-register c)
(setf (nes/cpu-register->sr-interrupt register) t)
(setf (nes/cpu-register->pc register) (nes/cpu-read c #xfffe :word))))
(defun nes/cpu--get-instruction-operand-and-cycle (c mode)
(let ((register (nes/cpu->register c)))
(case mode
(:accumulator
'(nil . 0))
(:implied
'(nil . 0))
(:immediate
(cons (nes/cpu--fetch c) 0))
(:relative
(let* ((base-addr (nes/cpu--fetch c))
(addr (if (< base-addr #x80)
(+ base-addr (nes/cpu-register->pc register))
(- (+ base-addr (nes/cpu-register->pc register)) 256)))
(cycle (if (not (eq (logand addr #xFF00) (logand (nes/cpu-register->pc register) #xFF00))) 1 0)))
(cons addr cycle)))
(:zero-page
(cons (nes/cpu--fetch c) 0))
(:zero-page-x
(cons (logand (+ (nes/cpu--fetch c)
(nes/cpu-register->idx-x register))
#xFF)
0))
(:zero-page-y
(cons (logand (+ (nes/cpu--fetch c)
(nes/cpu-register->idx-y register))
#xFF)
0))
(:absolute
(cons (nes/cpu--fetch c :word) 0))
(:absolute-x
(let* ((addr (nes/cpu--fetch c :word))
(idx-x (nes/cpu-register->idx-x register))
(cycle (if (eq (logand addr #xFF00) (logand (+ addr idx-x) #xFF00))
0 1)))
(cons (logand (+ addr idx-x) #xFFFF) cycle)))
(:absolute-y
(let* ((addr (nes/cpu--fetch c :word))
(idx-y (nes/cpu-register->idx-y register))
(cycle (if (eq (logand addr #xFF00) (logand (+ addr idx-y) #xFF00))
0 1)))
(cons (logand (+ addr idx-y) #xFFFF) cycle)))
(:pre-indexed-indirect
(let* ((base-addr (logand (+ (nes/cpu--fetch c) (nes/cpu-register->idx-x register))
#xFF))
(addr (logand (+ (nes/cpu-read c base-addr)
(lsh (nes/cpu-read c (logand (1+ base-addr) #xFF)) 8))
#xFFFF))
(cycle (if (/= (logand addr #xFF00) (logand base-addr #xFF00)) 1 0)))
(cons addr cycle)))
(:post-indexed-indirect
(let* ((data-addr (nes/cpu--fetch c))
(base-addr (+ (nes/cpu-read c data-addr)
(lsh (nes/cpu-read c (logand (1+ data-addr) #xFF)) 8)))
(addr (logand (+ base-addr (nes/cpu-register->idx-y register)) #xFFFF))
(cycle (if (/= (logand addr #xFF00) (logand base-addr #xFF00)) 1 0)))
(cons addr cycle)))
(:indirect-absolute
(let ((data-addr (nes/cpu--fetch c :word)))
(cons (logand (+ (nes/cpu-read c data-addr)
(lsh (nes/cpu-read c (logior (logand data-addr #xFF00)
(logand (1+ (logand data-addr #xFF)) #xFF)))
8))
#xFFFF)
0))))))
(defun nes/cpu--fetch (c &optional size)
(let ((size (or size :byte))
(addr (nes/cpu-register->pc (nes/cpu->register c))))
(incf (nes/cpu-register->pc (nes/cpu->register c)) (if (eq size :word) 2 1))
(nes/cpu-read c addr size)))
(defun nes/cpu-set-working-ram (cpu ram)
(setf (nes/cpu-bus->ram (nes/cpu->bus cpu)) ram))
(defun nes/cpu-set-program-rom (cpu rom-func)
(setf (nes/cpu-bus->prg-rom (nes/cpu->bus cpu)) rom-func))
(defun nes/cpu-step (c)
(when (nes/interrupt->nmi (nes/cpu->interrupt c))
(nes/cpu-nmi c))
(nes/interrupt-clear (nes/cpu->interrupt c))
(let* ((opcode (nes/cpu--fetch c))
(inst (aref nes/instruction:MAP opcode))
(operand-and-cycle (nes/cpu--get-instruction-operand-and-cycle c (nes/instruction->mode inst)))
(operand (car operand-and-cycle))
(inst-cycle (aref nes/instruction:CYCLES opcode))
(add-cycle (cdr operand-and-cycle)))
(setf (nes/cpu->cycles c) 0)
(funcall (nes/instruction->func inst) c operand (nes/instruction->mode inst))
(+ (nes/cpu->cycles c) inst-cycle add-cycle)
))
(defun nes/cpu-init (c)
(nes/cpu-reset c))
(provide 'nes-cpu)