writeusb

A Python script to write SAM Coupé disk images to a USB floppy drive so they can be used on real SAM hardware.

Source disk images should be normal 80/2/10/512 format and in MGT/SAD/EDSK disk image containers. SAMDOS/MasterDOS/BDOS and some custom loaders are supported.

Background

USB floppy drives are usually limited to 1.44M (18-sector) and 720K (9-sector) formats used by PC floppy disks. This is a problem for regular SAM disks, which use a 10-sector disk format.

This script re-maps the sectors used by the files on the source disk image so it uses only 9 sectors on each track. It also patches the boot loaders on converted disks to keep within these limits. Most SAM disks should support conversion.

Note: this script will NOT help to read existing 10-sector SAM Coupé disks. The 10th sector on each track is inaccessible on USB floppy drives.

Requirements

• Windows, Linux or macOS.
• USB floppy drive and double-density disks.
• Python 3.10 or later.

Windows users can install Python from the Windows Store.

Installation

To install:

python3 -m pip install mgtwriteusb

Or to install from local source code:

python3 -m pip install .

To upgrade to the latest version:

python3 -m pip install --upgrade mgtwriteusb

Command-line Options

usage: writeusb [-h] [-o OUTPUT] [-p] [-n] [-f] [-a] [-s] [-V] diskimage

Write SAM disk image to USB floppy drive

positional arguments:
  diskimage

options:
  -h, --help            show this help message and exit
  -o OUTPUT, --output OUTPUT
                        output to disk image file
  -p, --pad             pad output disk image to 10 sectors
  -n, --noverify        don't verify disk after writing
  -f, --force           write even if boot loader is unknown
  -a, --all             write all tracks, not just used tracks
  -s, --sniff           detect boot loader on source image
  -V, --version         show program's version number and exit

Examples

Convert image.dsk to 9-sector format, write used tracks to the connected USB floppy drive, then verify the written data:

writeusb image.dsk

Convert image.dsk to 9-sector format, save output to disk image output.img for use with SimCoupe or another disk writing program:

writeusb image.dsk -o output.img

Converting non-bootable disks will add a special version of SAMDOS v2, patched to dynamically support both 9-sector and 10-sector disks. It will appear in the directory listing as samdos9. When an existing boot loader is patched it supports only the converted 9-sector disks.

Troubleshooting

macOS and Linux users may need to run the script under sudo, depending on the permissions and group ownership of the USB floppy device. Linux users may just need to be in the disk group, depending on distribution.

Be sure to use real double-density media, which usually has a blue cover. High density disks have different magnetic properties, so covering the density hole is not a good solution. HD disks are often unreliable after writing (YMMV).

If you're re-using existing SAM disks be aware that some USB floppy drives may not recognise the existing 10-sector format. You may have to reformat the disk as true 9-sector before it'll work. Under Windows try format a: /t:80 /s:9, or under Linux try ufiformat /dev/sdX (change sdX to the correct device name).

SAMDOS/MasterDOS/BDOS will retry after disk errors but custom loaders may not. The MNEMOtech loader used by MNEMOdemo 1 and 2 fails immediately with a Loading Error so you'll need good quality disks!

Expect disk errors. If in doubt try a different disk!

Limitations

Disk images containing custom formats are not supported and will be rejected. This prevents original copies of Lemmings, Prince of Persia, and maybe some other titles from working.

Reducing from 10 sectors to 9 sectors also reduces the disk capacity. The converted disk has 72 directory slots and 702K of free space, rather than 80 directory slots and 780K on a regular disk. Full disks may need to be split.

Disks storing data outside the normal filesystem structures will be missed by the conversion process. This affects the Pac-Man Emulator (v1.4 or earlier).

https://github.com/simonowen/writeusb