izapple2/storage/fileNib.go
2020-10-17 20:10:48 +02:00

329 lines
9.1 KiB
Go

package storage
import (
"errors"
"fmt"
"os"
"strings"
)
/*
See:
"Beneath Apple DOS" https://fabiensanglard.net/fd_proxy/prince_of_persia/Beneath%20Apple%20DOS.pdf
https://github.com/TomHarte/CLK/wiki/Apple-GCR-disk-encoding
*/
const (
numberOfTracks = 35
numberOfSectors = 16
bytesPerSector = 256
bytesPerTrack = numberOfSectors * bytesPerSector
nibBytesPerTrack = 6656
nibImageSize = numberOfTracks * nibBytesPerTrack
dskImageSize = numberOfTracks * numberOfSectors * bytesPerSector
defaultVolumeTag = 254
cyclesPerBit = 4
)
type fileNib struct {
track [numberOfTracks][]byte
// Needed to write back
supportsWrite bool
filename string
logicalOrder *[16]int
}
func isFileNib(data []uint8) bool {
return len(data) == nibImageSize
}
func newFileNib(data []uint8) *fileNib {
var f fileNib
for i := 0; i < numberOfTracks; i++ {
f.track[i] = data[nibBytesPerTrack*i : nibBytesPerTrack*(i+1)]
}
return &f
}
func isFileDsk(data []uint8) bool {
return len(data) == dskImageSize
}
func newFileDsk(data []uint8, filename string) *fileNib {
var f fileNib
isPO := strings.HasSuffix(strings.ToLower(filename), "po")
f.logicalOrder = &dos33SectorsLogicalOrder
if isPO {
f.logicalOrder = &prodosSectorsLogicalOrder
}
f.filename = filename
f.supportsWrite = true
for i := 0; i < numberOfTracks; i++ {
trackData := data[i*bytesPerTrack : (i+1)*bytesPerTrack]
f.track[i] = nibEncodeTrack(trackData, defaultVolumeTag, byte(i), f.logicalOrder)
}
return &f
}
func (f *fileNib) saveTrack(track int) {
if f.supportsWrite {
file, err := os.OpenFile(f.filename, os.O_RDWR, 0)
if err != nil {
// We can't open the file for writing"
f.supportsWrite = false
fmt.Printf("Data can't be written for %v\n", f.filename)
}
data, err := nibDecodeTrack(f.track[track], f.logicalOrder)
if err != nil {
f.supportsWrite = false
fmt.Printf("Data written can't be decoded from nibbles\n")
}
offset := int64(track * bytesPerTrack)
_, err = file.WriteAt(data, offset)
if err != nil {
f.supportsWrite = false
fmt.Printf("Data can't be written\n")
}
}
}
func (f *fileNib) saveNib(filename string) error {
file, err := os.Create(filename)
if err != nil {
return err
}
defer file.Close()
for _, v := range f.track {
_, err := file.Write(v)
if err != nil {
return err
}
}
return nil
}
// See Beneath Apple DOS, figure 3.24
var dos33SectorsLogicalOrder = [16]int{
0x0, 0x7, 0xE, 0x6, 0xD, 0x5, 0xC, 0x4,
0xB, 0x3, 0xA, 0x2, 0x9, 0x1, 0x8, 0xF,
}
// See Beneath Apple ProDOS, figure 3.1
var prodosSectorsLogicalOrder = [16]int{
0x0, 0x8, 0x1, 0x9, 0x2, 0xA, 0x3, 0xB,
0x4, 0xC, 0x5, 0xD, 0x6, 0xE, 0x7, 0xF,
}
var sixAndTwoTranslateTable = [0x40]byte{
0x96, 0x97, 0x9a, 0x9b, 0x9d, 0x9e, 0x9f, 0xa6,
0xa7, 0xab, 0xac, 0xad, 0xae, 0xaf, 0xb2, 0xb3,
0xb4, 0xb5, 0xb6, 0xb7, 0xb9, 0xba, 0xbb, 0xbc,
0xbd, 0xbe, 0xbf, 0xcb, 0xcd, 0xce, 0xcf, 0xd3,
0xd6, 0xd7, 0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde,
0xdf, 0xe5, 0xe6, 0xe7, 0xe9, 0xea, 0xeb, 0xec,
0xed, 0xee, 0xef, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6,
0xf7, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff,
}
var sixAndTwoUntranslateTable = [256]int16{
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, 0, 1, -1, -1, 2, 3, -1, 4, 5, 6,
-1, -1, -1, -1, -1, -1, 7, 8, -1, -1, -1, 9, 10, 11, 12, 13,
-1, -1, 14, 15, 16, 17, 18, 19, -1, 20, 21, 22, 23, 24, 25, 26,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 27, -1, 28, 29, 30,
-1, -1, -1, 31, -1, -1, 32, 33, -1, 34, 35, 36, 37, 38, 39, 40,
-1, -1, -1, -1, -1, 41, 42, 43, -1, 44, 45, 46, 47, 48, 49, 50,
-1, -1, 51, 52, 53, 54, 55, 56, -1, 57, 58, 59, 60, 61, 62, 63,
}
const (
gap1Len = 48
gap2Len = 5
primaryBufferSize = bytesPerSector
secondaryBufferSize = bytesPerSector/3 + 1
)
func oddEvenEncodeByte(b byte) []byte {
/*
A byte is encoded in two bytes to make sure the bytes start with 1 and
does not have two consecutive zeros.
Data byte: D7-D6-D5-D4-D3-D2-D1-D0
result[0]: 1-D7- 1-D5- 1-D3- 1-D1
result[1]: 1-D6- 1-D4- 1-D2- 1-D0
*/
e := make([]byte, 2)
e[0] = ((b >> 1) & 0x55) | 0xaa
e[1] = (b & 0x55) | 0xaa
return e
}
func oddEvenDecodeByte(b0, b1 byte) byte {
/*
A byte is encoded in two bytes to make sure the bytes start with 1 and
does not have two consecutive zeros.
b0: 1-D7- 1-D5- 1-D3- 1-D1
b1: 1-D6- 1-D4- 1-D2- 1-D0
result: D7-D6-D5-D4-D3-D2-D1-D0
*/
return ((b0 & 0x55) << 1) | (b1 & 0x55)
}
const (
diskPrologByte1 = uint8(0xd5)
diskPrologByte2 = uint8(0xaa)
diskPrologByte3Address = uint8(0x96)
diskPrologByte3Data = uint8(0xad)
)
func nibEncodeTrack(data []byte, volume byte, track byte, logicalOrder *[16]int) []byte {
b := make([]byte, 0, nibBytesPerTrack) // Buffer slice with enough capacity
// Initialize gaps to be copied for each sector
gap1 := make([]byte, gap1Len)
for i := range gap1 {
gap1[i] = 0xff
}
gap2 := make([]byte, gap2Len)
for i := range gap2 {
gap2[i] = 0xff
}
for physicalSector := byte(0); physicalSector < numberOfSectors; physicalSector++ {
/* On the DSK file the sectors are in DOS3.3 logical order
but on the physical encoded track as well as in the nib
files they are in physical order.
*/
logicalSector := logicalOrder[physicalSector]
sectorData := data[logicalSector*bytesPerSector : (logicalSector+1)*bytesPerSector]
// 6and2 prenibbilizing.
primaryBuffer := make([]byte, primaryBufferSize)
secondaryBuffer := make([]byte, secondaryBufferSize)
for i, v := range sectorData {
// Primary buffer is easy: the 6 MSB
primaryBuffer[i] = v >> 2
// Secondary buffer: the 2 LSB reversed, shifted and in their place
shift := uint((i / secondaryBufferSize) * 2)
bit0 := ((v & 0x01) << 1) << shift
bit1 := ((v & 0x02) >> 1) << shift
position := i % secondaryBufferSize
secondaryBuffer[position] |= bit0 | bit1
}
// Render sector
// Address field
b = append(b, gap1...)
b = append(b, 0xd5, 0xaa, 0x96) // Address prolog
b = append(b, oddEvenEncodeByte(volume)...) // 4-4 encoded volume
b = append(b, oddEvenEncodeByte(track)...) // 4-4 encoded track
b = append(b, oddEvenEncodeByte(physicalSector)...) // 4-4 encoded sector
b = append(b, oddEvenEncodeByte(volume^track^physicalSector)...) // Checksum
b = append(b, 0xde, 0xaa, 0xeb) // Epilog
// Data field
b = append(b, gap2...)
b = append(b, 0xd5, 0xaa, 0xad) // Data prolog
prevV := byte(0)
for _, v := range secondaryBuffer {
b = append(b, sixAndTwoTranslateTable[v^prevV])
prevV = v
}
for _, v := range primaryBuffer {
b = append(b, sixAndTwoTranslateTable[v^prevV])
prevV = v
}
b = append(b, sixAndTwoTranslateTable[prevV]) // Checksum
b = append(b, 0xde, 0xaa, 0xeb) // Data epilog
}
return b
}
func findProlog(diskPrologByte3 uint8, data []byte, position int) int {
l := len(data)
for i := position; i < l; i++ {
if (data[i] == diskPrologByte1) &&
(data[(i+1)%l] == diskPrologByte2) &&
(data[(i+2)%l] == diskPrologByte3) {
return (i + 3) % l
}
}
return -1
}
func nibDecodeTrack(data []byte, logicalOrder *[16]int) ([]byte, error) {
b := make([]byte, bytesPerTrack) // Buffer slice with enough capacity
i := int(0)
l := len(data)
for {
// Find address field prolog
i = findProlog(diskPrologByte3Address, data, i)
if i == -1 {
break
}
// We just want the sector from the address field, we ignore the rest, no error detection
sector := oddEvenDecodeByte(data[(i+4)%l], data[(i+5)%l])
logicalSector := logicalOrder[sector]
dst := int(logicalSector) * bytesPerSector
// Find data prolog
i = (i + 8 + 3) % l // We skip the four two byte fields and the epilog
i = findProlog(diskPrologByte3Data, data, i)
// Read secondary buffer
prevV := byte(0)
for j := 0; j < secondaryBufferSize; j++ {
w := sixAndTwoUntranslateTable[data[i%l]]
if w == -1 {
return nil, errors.New("Invalid byte from nib data")
}
v := byte(w) ^ prevV
prevV = v
for k := 0; k < 3; k++ {
// The elements of the secondary buffer add two bits to three bytes
offset := j + k*secondaryBufferSize
if offset < bytesPerSector {
b[dst+offset] |= ((v & 0x02) >> 1) | ((v & 0x01) << 1)
}
v >>= 2
}
i++
}
// Read primary buffer
for j := 0; j < primaryBufferSize; j++ {
w := sixAndTwoUntranslateTable[data[i%l]]
if w == -1 {
return nil, errors.New("Invalid byte from nib data")
}
v := byte(w) ^ prevV
b[dst+j] |= v << 2 // The elements of the secondary buffer are the 6 MSB bits
prevV = v
i++
}
}
return b, nil
}