101 lines
2.8 KiB
Go
101 lines
2.8 KiB
Go
package storage
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import (
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"errors"
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"math/rand"
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)
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/*
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See:
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https://applesaucefdc.com/woz/
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*/
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type disketteWoz struct {
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data *FileWoz
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cycleOn uint64 // Cycle when the disk was last turned on
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turning bool
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latch uint8
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position uint32
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positionMax uint32 // As tracks may have different lengths position is related of positionMax of the las track
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cycle uint64
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mc3470Buffer uint8 // Four bit buffer to detect weak bits and to add latency
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visibleLatch uint8
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visibleLatchCountDown int8 // The visible latch stores a valid latch reading for 2 bit timings
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}
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func newDisquetteWoz(f *FileWoz) (*disketteWoz, error) {
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// Discard not supported features
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if f.Info.DiskType != 1 {
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return nil, errors.New("Only 5.25 disks are supported")
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}
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if f.Info.BootSectorFormat == 2 { // Info not available in WOZ 1.0
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return nil, errors.New("Woz 13 sector disks are not supported")
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}
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var d disketteWoz
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d.data = f
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return &d, nil
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}
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func (d *disketteWoz) PowerOn(cycle uint64) {
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d.turning = true
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d.cycleOn = cycle
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}
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func (d *disketteWoz) PowerOff(_ uint64) {
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d.turning = false
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}
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func (d *disketteWoz) Read(quarterTrack int, cycle uint64) uint8 {
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// Count cycles to know how many bits have been read
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cycles := cycle - d.cycle
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deltaBits := cycles / cyclesPerBit // TODO: Use Woz optimal bit timing
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// Process bits from woz
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// TODO: avoid processing too many bits if delta is big
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for i := uint64(0); i < deltaBits; i++ {
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// Get next bit taking into account the MC3470 latency and weak bits
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var fluxBit bool
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fluxBit, d.position, d.positionMax = d.data.GetNextBitAndPosition(d.position, d.positionMax, quarterTrack)
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d.mc3470Buffer = (d.mc3470Buffer << 1) & 0x0f
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if fluxBit {
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d.mc3470Buffer++
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}
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bit := (d.mc3470Buffer >> 1) & 0x1 // Use the previous to last bit to add latency
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if d.mc3470Buffer == 0 && rand.Intn(100) < 3 {
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// Four consecutive zeros. It'a a fake bit.
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// Output a random value. 70% zero, 30% one
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bit = 1
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}
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d.latch = (d.latch << 1) + bit
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if d.latch >= 0x80 {
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// Valid byte, store value a bit longer and clear the internal latch
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//fmt.Printf("Valid 0x%.2x\n", d.latch)
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d.visibleLatch = d.latch
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d.visibleLatchCountDown = 1
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d.latch = 0
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} else if d.visibleLatchCountDown > 0 {
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// Continue showing the valid byte
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d.visibleLatchCountDown--
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} else {
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// The valid byte is lost, show the internal latch
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d.visibleLatch = d.latch
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}
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}
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//fmt.Printf("Visible: 0x%.2x, latch: 0x%.2x, bits: %v, cycles: %v\n", d.visibleLatch, d.latch, deltaBits, cycle-d.cycle)
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// Update the internal last cycle without losing the remainder not processed
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d.cycle += deltaBits * cyclesPerBit
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return d.visibleLatch
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}
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func (d *disketteWoz) Write(quarterTrack int, value uint8, _ uint64) {
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panic("Write not implemented on woz disk implementation")
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}
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