152 lines
3.4 KiB
Go
152 lines
3.4 KiB
Go
package apple2
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import (
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"io"
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)
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// See https://fabiensanglard.net/fd_proxy/prince_of_persia/Inside%20the%20Apple%20IIe.pdf
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// See https://i.stack.imgur.com/yn21s.gif
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type memoryManager struct {
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apple2 *Apple2
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// Map of assigned pages
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activeMemoryRead [256]memoryHandler
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activeMemoryWrite [256]memoryHandler
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// Pages prepared to be paged in and out
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physicalMainRAM *memoryRange // 0x0000 to 0xbfff, Up to 48 Kb
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physicalROM *memoryRange // 0xd000 to 0xffff, 12 Kb
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physicalROMe *memoryRange // 0xc000 to 0xcfff, Zero or 4bk in the Apple2e
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}
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type memoryHandler interface {
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peek(uint16) uint8
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poke(uint16, uint8)
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}
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const (
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ioC8Off uint16 = 0xCFFF
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)
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// Peek returns the data on the given address
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func (mmu *memoryManager) Peek(address uint16) uint8 {
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if address == ioC8Off {
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mmu.resetSlotExpansionRoms()
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}
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hi := uint8(address >> 8)
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mh := mmu.activeMemoryRead[hi]
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if mh == nil {
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return 0xf4 // Or some random number
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}
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return mh.peek(address)
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}
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// Poke sets the data at the given address
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func (mmu *memoryManager) Poke(address uint16, value uint8) {
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if address == ioC8Off {
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mmu.resetSlotExpansionRoms()
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}
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hi := uint8(address >> 8)
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mh := mmu.activeMemoryWrite[hi]
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if mh == nil {
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return
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}
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mh.poke(address, value)
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}
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func (mmu *memoryManager) setPages(begin uint8, end uint8, mh memoryHandler) {
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mmu.setPagesRead(begin, end, mh)
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mmu.setPagesWrite(begin, end, mh)
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}
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func (mmu *memoryManager) setPagesRead(begin uint8, end uint8, mh memoryHandler) {
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i := begin
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for {
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mmu.activeMemoryRead[i] = mh
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if i == end {
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break
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}
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i++
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}
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}
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func (mmu *memoryManager) setPagesWrite(begin uint8, end uint8, mh memoryHandler) {
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i := begin
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for {
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mmu.activeMemoryWrite[i] = mh
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if i == end {
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break
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}
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i++
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}
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}
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// When 0xcfff is accessed the card expansion rom is unassigned
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func (mmu *memoryManager) resetSlotExpansionRoms() {
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if mmu.apple2.io.isSoftSwitchActive(ioFlagIntCxRom) {
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// Ignore if the Apple2 shadow ROM is active
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return
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}
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mmu.setPagesRead(0xc8, 0xcf, nil)
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}
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func (mmu *memoryManager) resetRomPaging() {
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// Assign the first 12kb of ROM from 0xd000 to 0xffff
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mmu.setPagesRead(0xd0, 0xff, mmu.physicalROM)
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}
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func (mmu *memoryManager) resetBaseRamPaging() {
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// Assign the base RAM from 0x0000 to 0xbfff
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mmu.setPages(0x00, 0xbf, mmu.physicalMainRAM)
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}
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func newMemoryManager(a *Apple2, romFile string) *memoryManager {
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var mmu memoryManager
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mmu.apple2 = a
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ram := make([]uint8, 0xc000) // Reserve 48kb
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mmu.physicalMainRAM = newMemoryRange(0, ram)
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mmu.loadRom(romFile)
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mmu.resetBaseRamPaging()
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mmu.resetRomPaging()
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return &mmu
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}
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const (
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apple2RomSize = 12 * 1024
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apple2eRomSize = 16 * 1024
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)
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func (mmu *memoryManager) loadRom(filename string) {
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data := loadResource(filename)
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size := len(data)
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if size != apple2RomSize && size != apple2eRomSize {
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panic("Rom size not supported")
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}
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a := mmu.apple2
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romStart := 0
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if size == apple2eRomSize {
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// The extra 4kb ROM is first in the rom file.
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// It starts with 256 unused bytes not mapped to 0xc000.
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a.isApple2e = true
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extraRomSize := apple2eRomSize - apple2RomSize
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mmu.physicalROMe = newMemoryRange(0xc000, data[0:extraRomSize])
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romStart = extraRomSize
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}
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mmu.physicalROM = newMemoryRange(0xd000, data[romStart:])
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}
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func (mmu *memoryManager) save(w io.Writer) {
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mmu.physicalMainRAM.save(w)
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}
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func (mmu *memoryManager) load(r io.Reader) {
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mmu.physicalMainRAM.load(r)
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mmu.resetBaseRamPaging()
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}
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