Pi-Floppy v1.0

Preface

This tutorial is a minor adaptation of the "Make a Pi Zero W Smart USB flash drive" article on the MagPi magazine.
Original article here: https://magpi.raspberrypi.com/articles/pi-zero-w-smart-usb-flash-drive

Note that the original MagPi tutorial has a typo in Step 14:
ExecStart=/usr/local/share/usb_share.py should be ExecStart=/usr/local/share/usbshare.py.

Also, for the USB device to show up properly on windows and be writable (if that is desired),
you need to do sudo modprobe g_mass_storage file=/piusb.bin stall=0 ro=0 removable=1 in Step 10.

Otherwise, the MagPi tutorial still works as of 2022-02-07 on a Pi Zero 2 W.

Intro

This tutorial helps you make a Raspberry Pi (tested on a Pi Zero 2 W) into a remotely accessible floppy USB emulatior drive, for use with floppy disk to USB emulators (commonly sold on eBay). These devices can be used in any old machine that has a 3.5" floppy drive reader, I tested this on an ABB S4C+ controller.

You will need a Pi and a PC with Windows.

Note that while the special software that formats a USB drive for use with floppy-to-USB emulators creates 100 separate "floppys" on a single drive, this tutorial currently only allows you to use the first floppy-- index "000" on the emulator device.

Step 1: Set Up Your Pi

I prefer to use the Raspberry Pi Imager to set up Raspbian. I used the latest 32-bit Raspbian Bullseye release. I use the extra settings in the Raspberry Pi Imager to preload my Wi-Fi, account, locale and SSH settings onto the Pi Zero 2 W.

This means I can directly SSH into my Pi after flashing the OS onto the SD card.

I turn off the desktop environment with
sudo raspi-config

Step 2: USB Driver

sudo nano /boot/config.txt
Then append to a new line at the end of the file:
dtoverlay=dwc2
Save and exit (crtl+x, y)
sudo nano /etc/modules
Again, append to a new line at the end of the file:
dwc2

Step 3: Container File

For our floppy, we need at least 1.44MB * 100 = 144MB of space. The next line makes a 256MiB file:
sudo dd bs=1M if=/dev/zero of=/piflop.bin count=256
Format with FAT32:
sudo mkdosfs /piflop.bin -F 32 -I

Step 4: Set up USB Floppy Device

Now plug your Pi Zero 2 W into a Windows PC. Use the micro USB port in the middle, not the PWR IN port.

Enable mass storage mode:
sudo modprobe g_mass_storage file=/piflop.bin stall=0 ro=0 removable=1
Your drive should show up in Windows. It might ask you to format it, if so then format with FAT32, quick format.
Now format the drive with the USB_Floppy_Manager_v1.40i tool. The link is to a Google Drive share (not mine) that works as of 2022-02-07.
Now we need to enable mass storage mode on boot:
sudo nano /etc/rc.local
Append to a new line right above exit 0:
sudo modprobe g_mass_storage file=/piflop.bin stall=0 ro=0 removable=1

Step 5: Mount Container File

Make the directory to mount to:
sudo mkdir /mnt/floppy
And add it to fstab:
sudo nano /etc/fstab
Append to a new line at the end of the file:
/piflop.bin /mnt/floppy auto users,umask=000 0 2
Mount:
sudo mount -a

Step 6: Automate Device Reconnect

The USB device needs to be unmounted and remounted on the Windows PC (or floppy to USB emulator device) every time a file is changed for it to show up on the PC/emulator. We'll use (and slightly modify) the great script from the MagPi tutorial.
sudo pip3 install watchdog
cd /usr/local/share
sudo wget http://rpf.io/usbzw -O usbshare.py
sudo chmod +x usbshare.py
Now edit the script:
sudo nano usbshare.py
On the line that starts with CMD_MOUNT (line 7), change to this:
CMD_MOUNT = "modprobe g_mass_storage file=/piflop.bin stall=0 ro=0 removable=1"
On the line that starts with WATCH_PATH (line 11), change to this:
WATCH_PATH = "/mnt/floppy"
On the line that starts with ACT_TIME_OUT (line 13), change to this: (this decreases the idle wait time before the code unmounts and remounts the drive from 30 seconds to 2 seconds, you can experiment with different values).
ACT_TIME_OUT = 2
Now save the file.

Next, let's create the systemd service unit file:
cd /etc/systemd/system
sudo nano usbshare.service
Paste this into the file:

[Unit]
Description=USB Share Watchdog

[Service]
Type=simple
ExecStart=/usr/bin/python3 /usr/local/share/usbshare.py
Restart=always

[Install]
WantedBy=multi-user.target

Start the service:
sudo systemctl daemon-reload
sudo systemctl enable usbshare.service
sudo systemctl start usbshare.service

You can check the status of the service:
sudo systemctl status usbshare.service
It should be green.

Step 7: Set up Your File Sharing of Choice

The MagPi tutorial referenced in the beginning has a step on setting up Samba (Step 11), or you can also use NFS (nfs-kernel-server). Many good tutorials out there!

Step 8: Enjoy!