* Harmonize drive and disk type hierarchies
Before, the `XXXDrive` and `XXXDisk` type hierarchies were similar,
but not exactly the same. For example, `encoding` and `format` were
missing on some `XXXDisk` types where they existed on the `XXXDrive`
type. This change attempts to bring the hierarchies closer together.
However, the biggest visible consequence is the introduction of the
`FLOPPY_FORMATS` array and its associated `FloppyFormat` type. This
replaces `NIBBLE_FORMATS` in most places. A couple of new type guards
for disk formats and disks have been added as well.
All tests pass, everything compiles with no errors, and both WOZ and
nibble format disks load in the emulator.
* Move disk data to a `disk` field in the drive
Before, disk data was mixed in with state about the drive itself (like
track, motor phase, etc.). This made it hard to know exactly what data
was necessary for different image formats.
Now, the disk data is in a `disk` field whose type depends on the
drive type. This makes responisbility a bit easier.
One oddity, though, is that the `Drive` has metadata _and_ the `Disk`
has metadata. When a disk is in the drive, these should be `===`, but
when there is no disk in the drive, obviously only the drive metadata
is set.
All tests pass, everything compiles, and both WOZ and nibble disks
work in the emulator (both preact and classic).
* Squash the `Drive` type hierarchy
Before, the type of the drive depended on the type of the disk in the
drive. Thus, `NibbleDrive` contained a `NibbleDisk` and a `WozDrive`
contained a `WozDisk`. With the extraction of the disk data to a
single field, this type hierarchy makes no sense. Instead, it
suffices to check the type of the disk.
This change removes the `NibbleDrive` and `WozDrive` types and type
guards, checking the disk type where necessary. This change also
introduces the `NoFloppyDisk` type to represent the lack of a
disk. This allows the drive to have metadata, for one.
All tests pass, everything compiles, and both WOZ and nibble disks
work locally.
* Use more destructuring assignment
Now, more places use constructs like:
```TypeScript
const { metadata, readOnly, track, head, phase, dirty } = drive;
return {
disk: getDiskState(drive.disk),
metadata: {...metadata},
readOnly,
track,
head,
phase,
dirty,
};
```
* Remove the `Disk` object from the `Drive` object
This change splits out the disk objects into a record parallel to the
drive objects. The idea is that the `Drive` structure becomes a
representation of the state of the drive that is separate from the
disk image actually in the drive. This helps in an upcoming
refactoring.
This also changes the default empty disks to be writable. While odd,
the write protect switch should be in the "off" position since there
is no disk pressing on it.
Finally, `insertDisk` now resets the head position to 0 since there is
no way of preserving the head position across disks. (Even in the real
world, the motor-off delay plus spindle spin-down would make it
impossible to know the disk head position with any accuracy.)
* Add `DiskMetada` to the `Disk` interface
Before, metadata about the image, such as name, side, etc. was mixed
in with actual disk image information. This change breaks that
information into a separate structure called `DiskMetadata`.
Currently, the only two fields are `name` and `side`, but the idea is
that more fields could be added as necessary, like a description, a
scan of the disk or label, etc. In a follow-on change, the default
write-protection status will come from the metadata as well.
The current implementation copies the metadata when saving/restoring
state, loading disk images, etc. In the future, the metadata should
passed around until the format is required to change (like saving one
disk image format as another). Likewise, in the future, in may be
desirable to be able to override the disk image metadata with
user-supplied metadata. This could be use, for example, to
temporarily add or remove write-protection from a disk image.
All existing tests pass and the emulator builds with no errors.
* Rename `writeMode` to `q7`
Before, nibble disk emulation used the `writeMode` field to keep track
of whether the drive should be read from or written to, but the WOZ
emulation used `q7` to keep track of the same state.
This change renames `writeMode` to `q7` because it more accurately
reflects the state of the Disk II controller as specified in the
manuals, DOS source, and, especially, _Understanding the Apple //e_ by
Jim Sather.
* Remove the coil state
Before, `q` captured the state of the coils. But it was never read.
This change just deletes it.
* Use the bootstrap and sequencer ROMs with indirection
Before, the contents of the bootstrap ROM and sequencer ROM were set
directly on fields of the controller. These were not saved or
restored with the state in `getState` and `setState`. (It would have
been very space inefficient if they had).
Now, these ROMs are used from constants indexed by the number of
sectors the card supports. This, in turn, means that if the number of
sectors is saved with the state, it can be easily restored.
* Split out the Disk II controller state
This change factors the emulated hardware state into a separate
structure in the Disk II controller. The idea is that this hardware
state will be able to be shared with the WOZ and nibble disk code
instead of sharing _all_ of the controller state (like callbacks and
so forth).
* Factor out disk insertion
Before, several places in the code essentially inserted a new disk
image into the drive, which similar—but not always exactly the
same—code. Now there is an `insertDisk` method that is responsible
for inserting a new `FloppyDisk`.
All tests pass, everything compiles, manually tested nibble disks and
WOZ disks.
Before, the `drives` field was an `array[0..1]` of `Drive`, but all of
the methods took a `DriveNumber`, which was `[1..2]`. This meant that
code everywhere was always subtracting 1 from the drive number.
Now, `drives` is a `Record<DriveNumber, Drive>`, which means tha it
has indexes `1, 2` and there's no need to subtract 1 everywhere.
This change updates the `DiskII` class and its tests.
The motivation for this change is to slowly split the WOZ disk
implementation from the nibble disk implementation. I've tried twice,
but the change has always grown too big and hairy, so I'm starting
very small this time and working my way up.
* Add a basic write test for WOZ images
The new test just tries to change some random nibbles at the beginning
of the image and then verifies that the change has been recorded.
This exposed a bug where `q7` was never set to `true` when write mode
was toggled on.
Also, the assumptions and limitations of `moveHead` are more clearly
documented.
* Address comments
* Improved `moveHead` documentation a bit more.
* Removed redundant variable in `readNibble`.
* Refactored `findSector` and commented out the chatty log line.
All tests pass. No lint warnings.
* Add a test for the dirty callback on writes
This new test just checks that a clean disk becomes dirty after a
write _and_ that the dirty callback is fired.
* Add tests for WOZ disks
The new tests verify the basic read behavior of the state sequencer on
well-behaved disks, including sync bytes and so on. Write tests are
still to come.
There's also a change to the Woz format to return the info chunk data
as well.
* Add tests for the DiskII card
This change adds basic read tests for nibble-based disks for the
DiskII card and fixes a few minor errors.
These tests are in preparation for refactoring.
* Add write tests
These are some basic tests of writing to nibble disks. In the process,
one minor bug was found, fixed and documented.
* Fix the write tests
I misinterpreted something from Sather and thought that the high bit
had to be set on the data for writing to happen at all. This is not
true. Instead, there is a flux transition every time the high bit is
set as the data is left-shifted out of the data register. The
erroneous test has been removed.
At the same time, I finally understand what `skip` does and documented
that.
* Add tests for saving and restoring Disk II state
These are not exhaustive tests, but they ensure that some basic state
is saved and restored.
