mirror of
https://github.com/davidgiven/fluxengine.git
synced 2025-10-31 11:17:01 -07:00
107 lines
4.7 KiB
Markdown
107 lines
4.7 KiB
Markdown
Disk: Generic IBM
|
|
=================
|
|
|
|
IBM scheme disks are _the_ most common disk format, ever. They're used by a
|
|
huge variety of different systems, and they come in a huge variety of different
|
|
forms, but they're all fundamentally the same: either FM or MFM, either single
|
|
or double sided, with distinct sector header and data records and no sector
|
|
metadata. Systems which use IBM scheme disks include but are not limited to:
|
|
|
|
- IBM PCs (naturally)
|
|
- Atari ST
|
|
- late era Apple machines
|
|
- Acorn machines
|
|
- the TRS-80
|
|
- late era Commodore machines (the 1571 and so on)
|
|
- most CP/M machines
|
|
- etc
|
|
|
|
FluxEngine supports reading these. However, some variants are more peculiar
|
|
than others, and as a result there are specific decoders which set the defaults
|
|
correctly for certain formats (for example: on PC disks the sector numbers
|
|
start from 1, but on [Acorn](disk-acorndfs.md) disks they start from 0). The
|
|
IBM decoder described here is the generic one, and is suited for 'conventional'
|
|
PC disks. While you can read all the variant formats with it if you use the
|
|
right set of arguments, it's easier to use the specific decoder.
|
|
|
|
The generic decoder is mostly self-configuring, and will detect the format of
|
|
your disk for you.
|
|
|
|
|
|
Reading disks
|
|
-------------
|
|
|
|
Just do:
|
|
|
|
fluxengine read `<format>`
|
|
|
|
...and you'll end up with an `ibm.img` file. This should work on most PC disks
|
|
(including FM 360kB disks, 3.5" 1440kB disks, 5.25" 1200kB disks, etc.) The size
|
|
of the disk image will vary depending on the format.
|
|
|
|
The common PC formats are `ibm720` and `ibm1440`, but there are _many_ others,
|
|
and there's too many configuration options to usefully list. Use `fluxengine
|
|
write` to list all formats, and try `fluxengine write ibm1440 --config` to see
|
|
a sample configuration.
|
|
|
|
Configuration options you'll want include:
|
|
|
|
- `--decoder.ibm.sector_id_base=N`: specifies the ID of the first sector;
|
|
this defaults to 1. Some formats (like the Acorn ones) start at 0. This
|
|
can't be autodetected because FluxEngine can't distinguish between a disk
|
|
which starts at sector 1 and a disk which starts at sector 0 but all the
|
|
sector 0s are missing.
|
|
|
|
- `--decoder.ibm.ignore_side_byte=true|false`: each sector header describes
|
|
the location of the sector: sector ID, track and side. Some formats use the
|
|
wrong side ID, so the sectors on side 1 are labelled as belonging to side
|
|
0. This causes FluxEngine to see duplicate sectors (as it can't distinguish
|
|
between the two sides). This option tells FluxEngine to ignore the side
|
|
byte completely and use the physical side instead.
|
|
|
|
- `--decoder.ibm.required_sectors=range`: if you know how many sectors to
|
|
expect per track, you can improve reads by telling FluxEngine what to
|
|
expect here. If a track is read and a sector on this list is _not_ present,
|
|
then FluxEngine assumes the read failed and will retry. This avoids the
|
|
situation where FluxEngine can't tell the difference between a sector
|
|
missing because it's bad or a sector missing because it was never written
|
|
in the first place. If sectors are seen outside the range here, it will
|
|
still be read. You can use the same syntax as for track specifiers: e.g.
|
|
`0-9`, `0,1,2,3`, etc.
|
|
|
|
|
|
Writing disks
|
|
-------------
|
|
|
|
FluxEngine can also write IBM scheme disks. Unfortunately the format is
|
|
incredibly flexible and you need to specify every single parameter, which
|
|
makes things slightly awkward. Preconfigured profiles are available.
|
|
|
|
The syntax is:
|
|
|
|
fluxengine write <format> -i input.img <options>
|
|
|
|
The common PC formats are `ibm720` and `ibm1440`, but there are _many_ others,
|
|
and there's too many configuration options to usefully list. Use `fluxengine
|
|
write` to list all formats, and try `fluxengine write ibm1440 --config` to see
|
|
a sample configuration.
|
|
|
|
Mixed-format disks
|
|
------------------
|
|
|
|
Some disks, usually those belonging to early CP/M machines, have more than one
|
|
format on the disk at once. Typically, the first few tracks will be low-density
|
|
FM encoded and will be read by the machine's ROM; those tracks contain new
|
|
floppy drive handling code capable of coping with MFM data, and so the rest of
|
|
the disk will use that, allowing them to store more data.
|
|
|
|
FluxEngine can read these fine, but it tends to get a bit confused when it sees
|
|
tracks with differing numbers of sectors --- if track 0 has 32 sectors but
|
|
track 1 has 16, it will assume that sectors 16..31 are missing on track 1 and
|
|
size the image file accordingly. This can be worked around by specifying the
|
|
size of each track; see the `eco1` read profile for an example.
|
|
|
|
Writing can be made to work too, but there is currently no example. Please [get
|
|
in touch](https://github.com/davidgiven/fluxengine/issues/new) if you have
|
|
specific requirements (nothing's come up yet).
|