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