izapple2/apple2/memoryManager.go
2019-03-02 20:41:25 +01:00

95 lines
2.5 KiB
Go

package apple2
// 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
activeMemory [256]memoryPage
// Pages prepared to be paged in and out
physicalMainRAM []ramPage // 0x0000 to 0xbfff, Up to 48 Kb
physicalROM []romPage // 0xd000 to 0xffff, 12 Kb
physicalROMe []romPage // 0xc000 to 0xcfff, Zero or 4bk in the Apple2e
unassignedExpansionROM []unassignedPage // 0xc000 to 0xcfff
}
// memoryPage is a data page of 256 bytes
type memoryPage interface {
Peek(uint8) uint8
Poke(uint8, 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)
lo := uint8(address)
return mmu.activeMemory[hi].Peek(lo)
}
// 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)
lo := uint8(address)
mmu.activeMemory[hi].Poke(lo, value)
}
// SetPage assigns a MemoryPage implementation on the page given
func (mmu *memoryManager) setPage(index uint8, page memoryPage) {
//fmt.Printf("Assigning page 0x%02x type %s\n", index, reflect.TypeOf(page))
mmu.activeMemory[index] = page
}
// When 0xcfff is accessed the card expansion rom is unassigned
func (mmu *memoryManager) resetSlotExpansionRoms() {
if mmu.apple2.io.isSoftSwitchExtActive(ioFlagIntCxRom) {
// Ignore if the Apple2 shadow ROM is active
return
}
for i := 8; i < 16; i++ {
p := mmu.unassignedExpansionROM[i]
mmu.setPage(uint8(i+0xc0), &p)
}
}
func newMemoryManager(a *Apple2) *memoryManager {
var mmu memoryManager
mmu.apple2 = a
// Assign RAM from 0x0000 to 0xbfff, 48kb
mmu.physicalMainRAM = make([]ramPage, 0xc0)
for i := 0; i <= 0xbf; i++ {
mmu.setPage(uint8(i), &(mmu.physicalMainRAM[i]))
}
// Set the 0xc100 to 0xcfff as unasigned, 4kb. It wil be taken by slot cards.
mmu.unassignedExpansionROM = make([]unassignedPage, 0x10)
for i := 1; i < 0x10; i++ {
page := uint8(i + 0xc0)
p := &mmu.unassignedExpansionROM[i]
p.page = page
mmu.setPage(page, p)
}
return &mmu
}
func (mmu *memoryManager) resetPaging() {
// Assign the first 12kb of ROM from 0xd000 to 0xfff
for i := 0xd0; i <= 0xff; i++ {
mmu.setPage(uint8(i), &(mmu.physicalROM[i-0xd0]))
}
}