mirror of
https://github.com/freewilll/apple2-go.git
synced 2024-09-30 21:56:59 +00:00
234 lines
6.3 KiB
Go
234 lines
6.3 KiB
Go
|
package mmu
|
||
|
|
||
|
import (
|
||
|
"fmt"
|
||
|
"io/ioutil"
|
||
|
)
|
||
|
|
||
|
const tracksPerDisk = 35
|
||
|
const sectorsPerTrack = 16
|
||
|
const imageLength = tracksPerDisk * sectorsPerTrack * 0x100
|
||
|
|
||
|
// Each sector has
|
||
|
// Address field prologue 0x003 bytes
|
||
|
// Volume, Track, Sector, Checksum 0x008 bytes
|
||
|
// Address field epilogue 0x003 bytes
|
||
|
// Data prologue 0x003 bytes
|
||
|
// 2-bits 0x056 bytes
|
||
|
// 6-bits 0x100 bytes
|
||
|
// checksum 0x001 byte
|
||
|
// Data epilogue 0x003 bytes
|
||
|
const diskSectorBytes = 3 + 8 + 3 + 3 + 0x56 + 0x100 + 1 + 3
|
||
|
const trackDataBytes = sectorsPerTrack * diskSectorBytes
|
||
|
|
||
|
var dos33SectorInterleaving [16]uint8
|
||
|
var translateTable62 [0x40]uint8 // Conversion of a 6 bit byte to a 8 bit "disk" byte
|
||
|
|
||
|
type sector struct {
|
||
|
data [0x100]uint8
|
||
|
}
|
||
|
|
||
|
type track struct {
|
||
|
sectors [sectorsPerTrack]sector
|
||
|
}
|
||
|
|
||
|
type disk struct {
|
||
|
tracks [tracksPerDisk]track
|
||
|
}
|
||
|
|
||
|
var image disk // A loaded disk image
|
||
|
var TrackData [trackDataBytes]uint8 // Converted image data as it it returned by the disk controller for a single track
|
||
|
|
||
|
func InitDiskImage() {
|
||
|
// Map DOS 3.3 sector interleaving
|
||
|
// Physical sector -> Logical sector
|
||
|
dos33SectorInterleaving[0x0] = 0x0
|
||
|
dos33SectorInterleaving[0x1] = 0x7
|
||
|
dos33SectorInterleaving[0x2] = 0xe
|
||
|
dos33SectorInterleaving[0x3] = 0x6
|
||
|
dos33SectorInterleaving[0x4] = 0xd
|
||
|
dos33SectorInterleaving[0x5] = 0x5
|
||
|
dos33SectorInterleaving[0x6] = 0xc
|
||
|
dos33SectorInterleaving[0x7] = 0x4
|
||
|
dos33SectorInterleaving[0x8] = 0xb
|
||
|
dos33SectorInterleaving[0x9] = 0x3
|
||
|
dos33SectorInterleaving[0xa] = 0xa
|
||
|
dos33SectorInterleaving[0xb] = 0x2
|
||
|
dos33SectorInterleaving[0xc] = 0x9
|
||
|
dos33SectorInterleaving[0xd] = 0x1
|
||
|
dos33SectorInterleaving[0xe] = 0x8
|
||
|
dos33SectorInterleaving[0xf] = 0xf
|
||
|
|
||
|
// Zero disk image data
|
||
|
for t := 0; t < tracksPerDisk; t++ {
|
||
|
for s := 0; s < sectorsPerTrack; s++ {
|
||
|
for i := 0; i < 0x100; i++ {
|
||
|
image.tracks[t].sectors[s].data[i] = 0
|
||
|
}
|
||
|
}
|
||
|
}
|
||
|
|
||
|
// Convert a 6 bit "byte" to a 8 bit "disk" byte
|
||
|
translateTable62 = [0x40]uint8{
|
||
|
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,
|
||
|
}
|
||
|
}
|
||
|
|
||
|
func ReadDiskImage(path string) {
|
||
|
bytes, err := ioutil.ReadFile(path)
|
||
|
if err != nil {
|
||
|
panic(fmt.Sprintf("Unable to read ROM: %s", err))
|
||
|
}
|
||
|
|
||
|
if len(bytes) != imageLength {
|
||
|
panic(fmt.Sprintf("Disk image has invalid length %d, expected %d", len(bytes), imageLength))
|
||
|
}
|
||
|
|
||
|
pos := 0
|
||
|
for t := 0; t < tracksPerDisk; t++ {
|
||
|
for s := 0; s < sectorsPerTrack; s++ {
|
||
|
for i := 0; i < 0x100; i++ {
|
||
|
image.tracks[t].sectors[s].data[i] = bytes[pos]
|
||
|
pos++
|
||
|
}
|
||
|
}
|
||
|
}
|
||
|
}
|
||
|
|
||
|
// Encode a byte into two 4-bit bytes with odd-even encoding. This is used
|
||
|
// for the sector and data headers
|
||
|
func oddEvenEncode(data uint8) (uint8, uint8) {
|
||
|
bit0 := (data & 0x01) >> 0
|
||
|
bit1 := (data & 0x02) >> 1
|
||
|
bit2 := (data & 0x04) >> 2
|
||
|
bit3 := (data & 0x08) >> 3
|
||
|
bit4 := (data & 0x10) >> 4
|
||
|
bit5 := (data & 0x20) >> 5
|
||
|
bit6 := (data & 0x40) >> 6
|
||
|
bit7 := (data & 0x80) >> 7
|
||
|
|
||
|
l := 0xaa | (bit7 << 6) | (bit5 << 4) | (bit3 << 2) | (bit1)
|
||
|
h := 0xaa | (bit6 << 6) | (bit4 << 4) | (bit2 << 2) | (bit0)
|
||
|
return l, h
|
||
|
}
|
||
|
|
||
|
// Convert 8 bit bytes to 0x56 2-bit sections and 0x100 6 bit sections
|
||
|
func makeSectorData(s sector) (data [0x56 + 0x100]uint8) {
|
||
|
twoBitPos := 0x0
|
||
|
for i := 0; i < 0x100; i++ {
|
||
|
b := s.data[i]
|
||
|
bit0 := b & 0x1
|
||
|
bit1 := (b & 0x2) >> 1
|
||
|
data[twoBitPos] = (data[twoBitPos] >> 2) | (bit0 << 5) | (bit1 << 4)
|
||
|
data[i+0x56] = b >> 2
|
||
|
|
||
|
twoBitPos++
|
||
|
if twoBitPos == 0x56 {
|
||
|
twoBitPos = 0x0
|
||
|
}
|
||
|
}
|
||
|
|
||
|
// Make sure the bits for 2 remainders from the 256 divide by 3 are in the right place.
|
||
|
data[0x54] = (data[0x54] >> 2)
|
||
|
data[0x55] = (data[0x55] >> 2)
|
||
|
|
||
|
return
|
||
|
}
|
||
|
|
||
|
func clearTrackData() {
|
||
|
for i := 0; i < trackDataBytes; i++ {
|
||
|
TrackData[i] = 0
|
||
|
}
|
||
|
}
|
||
|
|
||
|
func MakeTrackData(armPosition uint8) {
|
||
|
// Tracks are present on even arm positions.
|
||
|
track := armPosition / 2
|
||
|
|
||
|
// If it's an odd arm position or a track beyond the image, zero the data
|
||
|
if (armPosition >= (tracksPerDisk * 2)) || ((armPosition % 2) == 1) {
|
||
|
clearTrackData()
|
||
|
return
|
||
|
}
|
||
|
|
||
|
DriveState.BytePosition = 0 // Point the head at the first sector
|
||
|
|
||
|
// For each sector, encode the data and add it to TrackData
|
||
|
for physicalSector := 0; physicalSector < sectorsPerTrack; physicalSector++ {
|
||
|
logicalSector := dos33SectorInterleaving[physicalSector]
|
||
|
offset := int(physicalSector) * diskSectorBytes
|
||
|
|
||
|
volume := uint8(254) // Volume numbers aren't implemented
|
||
|
checksum := volume ^ track ^ uint8(physicalSector)
|
||
|
|
||
|
volL, volH := oddEvenEncode(volume)
|
||
|
trL, trH := oddEvenEncode(track)
|
||
|
seL, seH := oddEvenEncode(uint8(physicalSector))
|
||
|
csL, csH := oddEvenEncode(checksum)
|
||
|
|
||
|
// Address field prologue
|
||
|
TrackData[offset+0] = 0xd5
|
||
|
TrackData[offset+1] = 0xaa
|
||
|
TrackData[offset+2] = 0x96
|
||
|
|
||
|
// Volume, track, sector and checksum
|
||
|
TrackData[offset+3] = volL
|
||
|
TrackData[offset+4] = volH
|
||
|
TrackData[offset+5] = trL
|
||
|
TrackData[offset+6] = trH
|
||
|
TrackData[offset+7] = seL
|
||
|
TrackData[offset+8] = seH
|
||
|
TrackData[offset+9] = csL
|
||
|
TrackData[offset+10] = csH
|
||
|
|
||
|
// Address epilogue
|
||
|
TrackData[offset+11] = 0xde
|
||
|
TrackData[offset+12] = 0xaa
|
||
|
TrackData[offset+13] = 0xeb
|
||
|
|
||
|
// Data field prologue
|
||
|
TrackData[offset+14] = 0xd5
|
||
|
TrackData[offset+15] = 0xaa
|
||
|
TrackData[offset+16] = 0xad
|
||
|
|
||
|
sectorData := makeSectorData(image.tracks[track].sectors[logicalSector])
|
||
|
|
||
|
// a is the previous byte's value
|
||
|
a := uint8(0)
|
||
|
for i := 0; i < 0x56+0x100; i++ {
|
||
|
a ^= sectorData[i]
|
||
|
b := translateTable62[a]
|
||
|
TrackData[offset+17+i] = b
|
||
|
a = sectorData[i]
|
||
|
}
|
||
|
|
||
|
// Set the checksum byte
|
||
|
TrackData[offset+17+0x56+0x100] = translateTable62[a]
|
||
|
|
||
|
// Data epilogue
|
||
|
TrackData[offset+17+0x56+0x100+1] = 0xde
|
||
|
TrackData[offset+17+0x56+0x100+2] = 0xaa
|
||
|
TrackData[offset+17+0x56+0x100+3] = 0xeb
|
||
|
|
||
|
}
|
||
|
}
|
||
|
|
||
|
// Read a byte from the disk head and spin the disk along
|
||
|
func ReadTrackData() (result uint8) {
|
||
|
result = TrackData[DriveState.BytePosition]
|
||
|
|
||
|
DriveState.BytePosition++
|
||
|
if DriveState.BytePosition == trackDataBytes {
|
||
|
DriveState.BytePosition = 0
|
||
|
}
|
||
|
|
||
|
return
|
||
|
}
|