izapple2/disketteWoz.go
2019-12-22 14:37:19 +01:00

130 lines
3.5 KiB
Go

package apple2
import (
"errors"
"math/rand"
)
/*
See:
https://applesaucefdc.com/woz/
Emulation status for the disk used on the reference:
- How to begin
- DOS 3.3: Works
- * DOS 3.2: Not working, 13 sector disks can't boot
- Next choices
- Bouncing Kamungas: Works
- *** Commando: Not working
- Planetfall: Working
- Rescue Raiders: Working
- *** Sammy Lightfoot: Not working
- Stargate: Working
- Cross track sync
- *** Blazing Paddles: Not working
- *** Take 1: Not working
- *** Hard Hat Mack: Not working
- Half tracks
- The Bilestoad: Working
- Even more bit fiddling
- Dino Eggs: Working
- Crisis Mountain: Working
- Miner 2049er II: Working
- When bits aren't really bits
- The Print Shop Companion: Working
- What is the lifespan of the data latch?
- *** First Math Adventures - Understanding Word Problems
- Reading Offset Data Streams
- *** Wings of Fury: Not working
- Stickybear Town Builder: Working
- Optimal bit timing of WOZ 2,0
- * Border Zone: Unknown, there is no UI to swap disks
*/
type disketteWoz struct {
data *fileWoz
cycleOn uint64 // Cycle when the disk was last turned on
turning bool
latch uint8
position uint32
cycle uint64
trackSize uint32
mc3470Buffer uint8 // Four bit buffer to detect weak bits and to add latency
visibleLatch uint8
visibleLatchCountDown int8 // The visible latch stores a valid latch reading for 2 bit timings
}
func newDisquetteWoz(f *fileWoz) (*disketteWoz, error) {
// Discard not supported features
if f.info.DiskType != 1 {
return nil, errors.New("Only 5.25 disks are supported")
}
if f.info.BootSectorFormat == 2 { // Info not available in WOZ 1.0
return nil, errors.New("Woz 13 sector disks are not supported")
}
var d disketteWoz
d.data = f
return &d, nil
}
func (d *disketteWoz) powerOn(cycle uint64) {
d.turning = true
d.cycleOn = cycle
}
func (d *disketteWoz) powerOff(_ uint64) {
d.turning = false
}
func (d *disketteWoz) read(quarterTrack int, cycle uint64) uint8 {
// Count cycles to know how many bits have been read
cycles := cycle - d.cycle
deltaBits := cycles / cyclesPerBit // TODO: Use Woz optimal bit timing
// Process bits from woz
// TODO: avoid processing too many bits if delta is big
for i := uint64(0); i < deltaBits; i++ {
// Get next bit taking into account the MC3470 latency and weak bits
d.position++
fluxBit := d.data.getBit(d.position, quarterTrack)
d.mc3470Buffer = (d.mc3470Buffer<<1 + fluxBit) & 0x0f
bit := (d.mc3470Buffer >> 1) & 0x1 // Use the previous to last bit to add latency
if d.mc3470Buffer == 0 && rand.Intn(100) < 3 {
// Four consecutive zeros.It'a a fake bit.
// Output a random value. 70% zero, 30% one
bit = 1
}
d.latch = (d.latch << 1) + bit
if d.latch >= 0x80 {
// Valid byte, store value a bit longer and clear the internal latch
//fmt.Printf("Valid 0x%.2x\n", d.latch)
d.visibleLatch = d.latch
d.visibleLatchCountDown = 1
d.latch = 0
} else if d.visibleLatchCountDown > 0 {
// Continue showing the valid byte
d.visibleLatchCountDown--
} else {
// The valid byte is lost, show the internal latch
d.visibleLatch = d.latch
}
}
//fmt.Printf("Visible: 0x%.2x, latch: 0x%.2x, bits: %v, cycles: %v\n", d.visibleLatch, d.latch, deltaBits, cycle-d.cycle)
// Update the internal last cycle without losing the remainder not processed
d.cycle += deltaBits * cyclesPerBit
return d.visibleLatch
}
func (d *disketteWoz) write(quarterTrack int, value uint8, _ uint64) {
panic("Write not implemented on woz disk implementation")
}