izapple2/base64aRom.go
2019-11-09 18:13:19 +01:00

81 lines
2.0 KiB
Go

package apple2
import (
"fmt"
)
/*
Copam BASE64A uses paginated ROM
*/
// Base64aROM Models the paginated ROM on a BASE64A clone
type base64aROM struct {
romBanks [4]*memoryRange
romBank uint8
}
const (
// There are 6 ROM chips. Each can have 4Kb or 8Kb. They can fill
// 2 or 4 banks with 2kb windows.
base64aRomBankSize = 12 * 1024
base64aRomBankCount = 4
base64aRomWindowSize = 2 * 1024
base64aRomChipCount = 6
)
func loadBase64aRom(a *Apple2) error {
// Load the 6 PROM dumps
romBanksBytes := make([][]uint8, base64aRomBankCount)
for j := range romBanksBytes {
romBanksBytes[j] = make([]uint8, 0, base64aRomBankSize)
}
for i := 0; i < base64aRomChipCount; i++ {
filename := fmt.Sprintf("<internal>/BASE64A_%X.BIN", 0xd0+i*0x08)
data, err := loadResource(filename)
if err != nil {
return err
}
for j := range romBanksBytes {
start := (j * base64aRomWindowSize) % len(data)
romBanksBytes[j] = append(romBanksBytes[j], data[start:start+base64aRomWindowSize]...)
}
}
// Create banks
var r base64aROM
for j := range romBanksBytes {
r.romBanks[j] = newMemoryRange(0xd000, romBanksBytes[j])
}
// Start with first bank active
r.changeBank(a.mmu, 0)
// Add rom soft switches. They use the annunciator 0 and 1
a.io.addSoftSwitchRW(0x58, func(*ioC0Page) uint8 {
r.changeBank(a.mmu, r.romBank&2)
return 0
}, "ANN0OFF-ROM")
a.io.addSoftSwitchRW(0x59, func(*ioC0Page) uint8 {
r.changeBank(a.mmu, r.romBank|1)
return 0
}, "ANN0ON-ROM")
a.io.addSoftSwitchRW(0x5A, func(*ioC0Page) uint8 {
r.changeBank(a.mmu, r.romBank&1)
return 0
}, "ANN1OFF-ROM")
a.io.addSoftSwitchRW(0x5B, func(*ioC0Page) uint8 {
r.changeBank(a.mmu, r.romBank|2)
return 0
}, "ANN1ON-ROM")
return nil
}
func (r *base64aROM) changeBank(mmu *memoryManager, bank uint8) {
r.romBank = bank
//fmt.Printf("Change to ROM bank #%v\n", r.romBank)
mmu.physicalROM = r.romBanks[r.romBank]
mmu.resetRomPaging() // If rom was not active. This is going too far?
}