izapple2/romX.go

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package izapple2
import (
"fmt"
"github.com/ivanizag/iz6502"
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)
/*
RomX from https://theromexchange.com/
This complement uses the RomX API spec to switch main ROM and character generator ROM
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Only the font switch is implemented
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See:
https://theromexchange.com/documentation/ROM%20X%20API%20Reference.pdf
https://theromexchange.com/downloads/ROM%20X%2020-10-22.zip
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https://theromexchange.com/documentation/romxce/ROMXce%20API%20Reference.pdf
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For romX:
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It is not enough to intercept the ROM accesses. RomX intercept the 74LS138 in
position F12, that has access to the full 0xc000-0xf000 on the Apple II+
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Firmware:
- It first copies $D000-$DFFF to $6000 and runs there.
go run *.go -rom ROMX.FIRM.dump -disk ROM\ X\ 20-10-22.dsk
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*/
type romX struct {
a *Apple2
memory iz6502.Memory
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activationStep int
systemBank uint8
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mainBank uint8
tempBank uint8
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textBank uint8
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debug bool
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}
var romXActivationSequence = []uint16{0xcaca, 0xcaca, 0xcafe}
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var romXceActivationSequence = []uint16{0xfaca, 0xfaca, 0xfafe}
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const (
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romxSetupBank = uint8(0)
romXPlusSetSystemBankBaseAddress = uint16(0xcef0)
romXPlusSetTextBankBaseAddress = uint16(0xcfd0)
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// Unknown
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//romXFirmwareMark0Address = uint16(0xdffe)
//romXFirmwareMark0Value = uint8(0x4a)
//romXFirmwareMark1Address = uint16(0xdfff)
//romXFirmwareMark1Value = uint8(0xcd)
romXceSelectTempBank = uint16(0xf850)
romXceSelectMainBank = uint16(0xf851)
romXceSetTempBank = uint16(0xf830) // 16 positions
romXceSetMainBank = uint16(0xf800) // 16 positions
romXcePresetTextBank = uint16(0xf810) // 16 positions
romXceMCP7940SDC = uint16(0xf860) // 16 positions
romXceLowerUpperBanks = uint16(0xf820) // 16 positions
romXGetDefaultSystemBank = uint16(0xd034) // $00 to $0f
romXGetDefaultTextBank = uint16(0xd02e) // $10 to $1f
romXGetCurrentBootDelay = uint16(0xdeca) // $00 to $0f
/*
romXceEntryPointSetClock = uint16(0xc803)
romXceEntryPointReadClock = uint16(0xc803)
romXceEntryPointLauncherToRam = uint16(0xdfd9)
romXceEntryPointLauncher = uint16(0xdfd0)
*/
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)
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func newRomX(a *Apple2) (*romX, error) {
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var rx romX
rx.a = a
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rx.memory = a.mmu
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rx.systemBank = 1
rx.mainBank = 1
rx.tempBank = 1
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rx.textBank = 0
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rx.debug = true
if a.isApple2e {
err := a.cg.load("<internal>/ROMXce Production 1Mb Text ROM V5.bin")
if err != nil {
return nil, err
}
}
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// Intercept all memory accesses
a.cpu.SetMemory(&rx)
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return &rx, nil
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}
func (rx *romX) Peek(address uint16) uint8 {
intercepted, value := rx.interceptAccess(address)
if intercepted {
return value
}
return rx.memory.Peek(address)
}
func (rx *romX) PeekCode(address uint16) uint8 {
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intercepted, value := rx.interceptAccess(address)
if intercepted {
return value
}
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return rx.memory.PeekCode(address)
}
func (rx *romX) Poke(address uint16, value uint8) {
rx.interceptAccess(address)
rx.memory.Poke(address, value)
}
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func (rx *romX) logf(format string, a ...interface{}) {
msg := fmt.Sprintf(format, a...)
fmt.Printf("[romX]%s\n", msg)
}
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func (rx *romX) interceptAccess(address uint16) (bool, uint8) {
// Intercept only $C080 to $FFFF as seen by the F12 chip
if address < 0xc080 {
return false, 0
}
// Setup mode when the setup bank is active
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if rx.systemBank == romxSetupBank {
// Range commands
nibble := uint8(address & 0xf)
switch address & 0xfff0 {
case romXceSetMainBank:
rx.mainBank = nibble
rx.logf("Main bank set to $%x", nibble)
case romXcePresetTextBank:
textBank := int(nibble)
rx.a.cg.setPage(textBank)
rx.logf("[romX]Text bank set to $%x", nibble)
case romXceLowerUpperBanks:
rx.logf("Configure lower upper banks $%x", address)
case romXceSetTempBank:
rx.tempBank = nibble
rx.logf("Temp bank set to $%x", nibble)
case romXceMCP7940SDC:
rx.logf("Configure MCP7940 $%x", address)
}
// More commands
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switch address {
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case romXceSelectTempBank:
rx.systemBank = rx.tempBank
rx.logf("System bank set to temp bank $%x", rx.systemBank)
case romXceSelectMainBank:
rx.systemBank = rx.mainBank
rx.logf("System bank set to main bank $%x", rx.systemBank)
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}
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// Queries
switch address {
case romXGetDefaultSystemBank:
bank := rx.systemBank
rx.logf("Peek in $%04x, current system bank %v", address, bank)
return true, bank
case romXGetDefaultTextBank:
page := uint8(rx.a.cg.getPage() & 0xf)
rx.logf("PeeK in $%04x, current text bank %v", address, page)
return true, 0x10 + page
case romXGetCurrentBootDelay:
delay := uint8(5) // We don't care
rx.logf("PeeK in $%04x, current boot delay %v", address, delay)
return true, delay
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}
return false, 0
}
// Activation sequence detection
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if address == romXceActivationSequence[rx.activationStep] {
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rx.activationStep++
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rx.logf("Activation step %v", rx.activationStep)
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if rx.activationStep == len(romXActivationSequence) {
// Activation sequence completed
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rx.systemBank = romxSetupBank
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rx.activationStep = 0
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rx.logf("System bank set to 0, %v", rx.systemBank)
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}
} else {
rx.activationStep = 0
}
return false, 0
}
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func setupRomX(a *Apple2) error {
_, err := newRomX(a)
if err != nil {
return err
}
return nil
}