izapple2/memoryManager.go
2019-06-01 20:06:44 +02:00

152 lines
3.4 KiB
Go

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