Added comments to disk package
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Will Angenent
parent
5e330c1373
commit
ec44175e62
72
disk/disk.go
72
disk/disk.go
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@ -9,7 +9,7 @@ import (
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const tracksPerDisk = 35
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const sectorsPerTrack = 16
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const imageLength = tracksPerDisk * sectorsPerTrack * 0x100
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const imageLength = tracksPerDisk * sectorsPerTrack * 0x100 // Number of bytes taken by a disk image
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// Each sector has
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// Address field prologue 0x003 bytes
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@ -20,12 +20,12 @@ const imageLength = tracksPerDisk * sectorsPerTrack * 0x100
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// 6-bits 0x100 bytes
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// checksum 0x001 byte
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// Data epilogue 0x003 bytes
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const diskSectorBytes = 3 + 8 + 3 + 3 + 0x56 + 0x100 + 1 + 3
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const trackDataBytes = sectorsPerTrack * diskSectorBytes
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const diskSectorBytes = 3 + 8 + 3 + 3 + 0x56 + 0x100 + 1 + 3 // Number of bytes one sector takes up on the disk
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const trackDataBytes = sectorsPerTrack * diskSectorBytes // Number of bytes one track takes up on the disk
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var dos33SectorInterleaving [16]uint8
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var sixTwoEncoding [0x40]uint8 // Conversion of a 6 bit byte to a 8 bit "disk" byte
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var sixTwoDecoding [0x100]uint8 // Conversion of a 8 bit "disk" byte to a 6 bit byte
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var sectorInterleaving [16]uint8 // A map of physical to logical sector
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var sixTwoEncoding [0x40]uint8 // Conversion of a 6 bit byte to a 8 bit "disk" byte
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var sixTwoDecoding [0x100]uint8 // Conversion of a 8 bit "disk" byte to a 6 bit byte
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type sector struct {
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data [0x100]uint8
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@ -61,11 +61,12 @@ type addressField struct {
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var lastReadAddress addressField
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var lastReadSectorDataPosition int
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// sectorWriteState keeps track of what write data has been received
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var sectorWriteState struct {
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State byte
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RawData [rawDataBufferSize]uint8
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RawDataPosition uint16
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Address addressField
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State byte // waitingforDataPrologue or receivingData
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RawData [rawDataBufferSize]uint8 // data as it is being written
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RawDataPosition uint16 // position in RawData
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Address addressField // address header of the last sector read
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}
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func resetsectorWriteState() {
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@ -73,25 +74,26 @@ func resetsectorWriteState() {
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sectorWriteState.RawDataPosition = 0
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}
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// InitDiskImage sets up some mapping variables and resets the write state
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func InitDiskImage() {
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// Map DOS 3.3 sector interleaving
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// Physical sector -> Logical sector
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dos33SectorInterleaving[0x0] = 0x0
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dos33SectorInterleaving[0x1] = 0x7
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dos33SectorInterleaving[0x2] = 0xe
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dos33SectorInterleaving[0x3] = 0x6
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dos33SectorInterleaving[0x4] = 0xd
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dos33SectorInterleaving[0x5] = 0x5
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dos33SectorInterleaving[0x6] = 0xc
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dos33SectorInterleaving[0x7] = 0x4
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dos33SectorInterleaving[0x8] = 0xb
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dos33SectorInterleaving[0x9] = 0x3
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dos33SectorInterleaving[0xa] = 0xa
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dos33SectorInterleaving[0xb] = 0x2
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dos33SectorInterleaving[0xc] = 0x9
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dos33SectorInterleaving[0xd] = 0x1
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dos33SectorInterleaving[0xe] = 0x8
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dos33SectorInterleaving[0xf] = 0xf
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sectorInterleaving[0x0] = 0x0
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sectorInterleaving[0x1] = 0x7
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sectorInterleaving[0x2] = 0xe
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sectorInterleaving[0x3] = 0x6
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sectorInterleaving[0x4] = 0xd
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sectorInterleaving[0x5] = 0x5
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sectorInterleaving[0x6] = 0xc
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sectorInterleaving[0x7] = 0x4
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sectorInterleaving[0x8] = 0xb
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sectorInterleaving[0x9] = 0x3
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sectorInterleaving[0xa] = 0xa
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sectorInterleaving[0xb] = 0x2
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sectorInterleaving[0xc] = 0x9
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sectorInterleaving[0xd] = 0x1
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sectorInterleaving[0xe] = 0x8
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sectorInterleaving[0xf] = 0xf
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// Zero disk image data
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for t := 0; t < tracksPerDisk; t++ {
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@ -121,6 +123,7 @@ func InitDiskImage() {
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resetsectorWriteState()
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}
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// InitDiskImage reads a disk image from file
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func ReadDiskImage(path string) {
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imagePath = path
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@ -146,6 +149,7 @@ func ReadDiskImage(path string) {
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imageIsDirty = false
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}
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// writeDiskImage writes a disk image to file
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func writeDiskImage() {
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bytes := make([]byte, tracksPerDisk*sectorsPerTrack*0x100)
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@ -210,6 +214,7 @@ func sectorDataEncode(s sector) (data [0x56 + 0x100]uint8) {
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return
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}
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// Convert 0x56 + 0x100 disk bytes into 0x100 sector bytes
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func sectorDataDecode(data []uint8) (sector [0x100]uint8) {
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for i := 0; i < 0x100; i++ {
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sector[i] = data[i+0x56]
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@ -236,8 +241,10 @@ func clearTrackData() {
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}
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}
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// makeSectorData converts the in-memory image data to disk encoded data in
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// trackData for a given track and sector.
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func makeSectorData(track uint8, physicalSector uint8) {
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logicalSector := dos33SectorInterleaving[physicalSector]
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logicalSector := sectorInterleaving[physicalSector]
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offset := int(physicalSector) * diskSectorBytes
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volume := uint8(254) // Volume numbers aren't implemented
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@ -293,6 +300,7 @@ func makeSectorData(track uint8, physicalSector uint8) {
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trackData[offset+17+0x56+0x100+3] = 0xeb
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}
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// MakeTrackData makes disk encoded data for a whole track when armPosition is even.
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func MakeTrackData(armPosition uint8) {
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// Tracks are present on even arm positions.
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track := uint8(armPosition / 2)
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@ -311,6 +319,8 @@ func MakeTrackData(armPosition uint8) {
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}
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}
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// decodeAddressField decodes the 6 bytes from a disk encoded sector address
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// field into 3 byte volume, track and sector.
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func decodeAddressField(data []uint8) addressField {
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var af addressField
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af.volume = oddEvenDecode(data[0], data[1])
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@ -323,6 +333,10 @@ func decodeAddressField(data []uint8) addressField {
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func ReadTrackData() (result uint8) {
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result = trackData[system.DriveState.BytePosition]
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// If the head is far along enough in the track, see if the head is on a
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// sector header and decode it. This is used by the write code since the
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// write code has to know what track and sector the head has just gone
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// past.
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if system.DriveState.BytePosition >= 9 {
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if trackData[system.DriveState.BytePosition-9] == 0xd5 &&
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trackData[system.DriveState.BytePosition-8] == 0xaa &&
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@ -334,6 +348,7 @@ func ReadTrackData() (result uint8) {
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}
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}
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// Go forward one byte and loop around.
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system.DriveState.BytePosition++
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if system.DriveState.BytePosition == trackDataBytes {
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system.DriveState.BytePosition = 0
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@ -383,7 +398,7 @@ func WriteTrackData(value uint8) {
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if sectorWriteState.RawDataPosition == 0x56+0x100 {
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// We have the full sector data
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physicalSector := lastReadAddress.sector
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logicalSector := dos33SectorInterleaving[physicalSector]
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logicalSector := sectorInterleaving[physicalSector]
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// transform the data from disk bytes to 6-bytes and EOR it
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a := uint8(0)
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@ -406,6 +421,7 @@ func WriteTrackData(value uint8) {
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}
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}
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// FlushImage writes the disk image file if it's been written to.
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func FlushImage() {
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if imageIsDirty {
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writeDiskImage()
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