Seeing that I am still receiving issues and questions about whether this will run on compatible microcontrollers such as LGT8F328P I felt the need for an explanation. At the time of me writing this fddEMU, Arduino nano (atmega328p) was one of the cheapest and widely available microcontrollers. I wanted something every electronics hobbyist && retro enthusiast can easily build and use. But the advent of raspberry pi pico (RP2040) -a very capable microcontroller both widely available and cheap- made this meaningless. Now fddEMU stays here as a curiosity.

fddEMU

An AVR (atmega328p) based floppy drive emulator for PC <br> <br> <br> <br> fddEMU is a DIY floppy drive emulator. You can immediately begin testing fddEMU on serial terminal with an arduino nano, an SD adapter that converts 5 volts arduino power supply and signals to 3.3 volts suitable for SD card, an SD card, and some jumper cables. Standalone (using without usb serial connection) require SSD1306 i2c screen, buttons and a 5 volts power supply. <br><br>

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A very compact and configurable PCB design for fddEMU (created by @ikonko)<br> Please check documentation and photos for compact PCB for detailed explanation and configuration options. Gerber files are available in hardware folder. <br><br>

Limitations <br>

• fddEMU is not an cycle exact floppy emulator , it is more of a hack (it's a bit slower than actual fdd) but it works because floppy controllers have sensible timeouts and we take advantage of that.
• fddEMU uses MFM encoding (used by HD and DD disks) so there is no FM encoding (used by SD disks) support as of now. But it is possible to implement FM encoding.
• fddEMU uses raw floppy images (images prepared with dd or rawread) does not require or use a MFM file. Converts raw image sectors to MFM on the fly using ArduinoFDC library.
• fddEMU supports fixed sector size of 512 bytes, other sector sizes are not supported.
• Requires a Floppy Drive Controller (FDC) on the PC side to communicate so it probably wont work with an Amiga. <br><br>

Hardware (Required)

• Arduino Nano or Arduino Pro Micro (UNO will do but button inputs require ADC7, use serial commands instead)
• Micro SD card adapter (converts 5 volts arduino power supply and signals to 3.3 volts)
• A micro SD card (formatted FAT16/32, floppy images in root directory)
• Two 1kOhm resistors for Step (pin 20 of floppy connector) and WriteData (pin 22 of floppy connector). Atmega's internal pullups are not sufficicient for parasitic capacitance of long floppy drive cable
• Male to female jumper wires (for connecting arduino nano pins to FDC ribbon cable)
• Male to male jumper wires (for pullup on step and readdata pins) <br>

Hardware (Optional)

• 0.96" i2c OLED (SSD1306) screen (for output)
• 4 or 5 1kOhm resistors (for making ADC buttons)
• 1 100kOhm resistor (ADC7 has no pullup, so an external pullup required)
• 4 or 5 push buttons (required for ADC input obviously)
• 5 volts power supply (Computer PSU 5v pins or an external PSU can be used)
• Female to female jumper wires (for connecting SD adapter to arduino nano)
• Breadboard or perfboard (for placing pullups and ADC buttons) <br><br>

Pin mapping (single drive) Arduino Pro Micro |Arduino Nano |FDD Ribbon Cable --------------------|---------------|---------------------- GND |GND |1 (GND) RX (PD2) |D2 (PD2) |20 (Step pulse) TX (PD3) |D3 (PD3) |18 (Direction) 8 (PB4) |D4 (PD4) |16 (Motor on B) 10 (PB6) |D5 (PD5) |12 (Drive Select B) 5 (PC6) |D6 (PD6) |32 (Select head) 6 (PD7) |D7 (PD7) |8 (Index pulse) 4 (PD4) |D8 (PB0) |22 (Write data) 9 (PB5) |D9 (PB1) |30 (Read data) 7 (PE6) |A0 (PC0) |24 (Write enable) A3 (PF4) |A1 (PC1) |26 (Track zero) 24 (PD5 - TXLED) |A2 (PC2) |28 (Write protect) A1 (PF6) |A3 (PC3) |34 (Disk changed)

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Pin mapping (dual drive) Arduino Pro Micro |Arduino Nano |FDD Ribbon Cable --------------------|---------------|---------------------- GND |GND |1 (GND) RX (PD2) |D2 (PD2) |20 (Step pulse) TX (PD3) |D3 (PD3) |18 (Direction) 8 (PB4) |D4 (PD4) |14 (Drive Select A) 10 (PB6) |D5 (PD5) |12 (Drive Select B) 5 (PC6) |D6 (PD6) |32 (Select head) 6 (PD7) |D7 (PD7) |8 (Index pulse) 4 (PD4) |D8 (PB0) |22 (Write data) 9 (PB5) |D9 (PB1) |30 (Read data) 7 (PE6) |A0 (PC0) |24 (Write enable) A3 (PF4) |A1 (PC1) |26 (Track zero) 24 (PD5 - TXLED) |A2 (PC2) |28 (Write protect) A1 (PF6) |A3 (PC3) |34 (Disk changed)

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Micro SD Adapter connections Arduino Pro Micro |Arduino Nano |Micro SD adapter --------------------|---------------|------------------- A0 (PF7) |D10 (PB2) |CS 16 (PB2) |D11 (PB3) |MOSI 14 (PB3) |D12 (PB4) |MISO 15 (PB1) |D13 (PB5) |SCK VCC |5V |VCC GND |GND |GND

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0.96" OLED SSD1306 connections Arduino Pro Micro |Arduino Nano |0.96" OLED SSD1306 --------------------|---------------|------------------- GND |GND |GND VCC |5V |VCC 2 (PD1) |A4 |SDA 3 (PD0) |A5 |SCL

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Resistor ladder for ADC buttons <br> Connected to pin A7 (ADC7) on Arduino Nano or pin A2 (PF5) on Arduino Pro Micro <br> <br><br>

Firmware <br> Download with submodules(u8glib & lufa): git clone https://github.com/acemielektron/fddEMU --recursive<br> If not downloaded with recursive option run (in fddEMU folder): git submodule update --init --recursive<br> Current Makefile assumes avr-gcc and avr-binutils are installed and are in the path, avr specific includes are in "/usr/avr/include" (arch) or "/usr/lib/avr/include" (ubuntu) <br> run make to build fddEMU.hex with default options. <br> build options:

• GUI: enables graphical user interface on OLED screen and ADC buttons (enabled default by Makefile).
• SERIAL: enables serial user interface and serial commands.
• VFFS: enables virtual disk.
• DEBUG: enables debug output on serial.
• FLIP: flips the image on OLED screen 180 degrees (enabled default by Makefile).
• WDT: enables watchdog timer (enabled default by Makefile).<br><br> These build options could either be switched on and off from Makefile or commandline (eg.: make DUAL=1 GUI=1 VFFS=1 SERIAL=0 DEBUG=0).<br> Flashing the mcu could also be done by Makefile. make flash programs "fddEMU.hex" to default serial port "/dev/ttyUSB0". If you want to use another serial port assign it to PORT variable (eg.: make flash PORT=/dev/ttyUSB2).

Note: Due to larger bootloader on Atmega32U4 and added code overhead for USB-Serial all features of fddEMU will be avaialble on Atmega32U4

Warning: Writing > 28K (28672 bytes) firmware to Arduino Pro Micro results in bootloader being overwritten and requires reprogramming the bootloader using external programmer (eg. USBASP). Please check output of avr-size at the end of make process and make sure it is < 28K. <br><br>

How to use<br>

• fddEMU looks for a boot record on "sector 0" of the image. If the boot record reports that the image is formatted as "FAT1?", sector size is 512, number of heads is 2 and number of tracks and number of sectors are less than 255 the image file is loaded with the settings provided by the boot record. To be able to read these custom FAT12 images host system should support provided number of tracks and sectors. If there is no boot record file size is compared to the standart floppy sizes (1.44M, 1.2M, 720K and 360K), if file size matches one of these sizes it is loaded as raw image.
• Image file must be contiguous for fddEMU to be able to load, if the file is not contiguous an error message will be shown and loading will fail.
• Contiguity check would take long for large files (> 2MB) during this check fddEMU can not be used.
• For booting a host system, on startup fddEmu looks for "BOOT.IMG" on SD card. If there is a "BOOT.IMG" on the SD card fddEMU tries to load this file to drive A.
• if image file has "read only" attribute set, fddEMU will report "Write Protected" to host system.
• To protect OLED screen fddEMU will put screen to sleep after some idle time, press "S1" (SELECT) button or "S" key inside serial terminal to wake screen up.
• When host is reading/writing one of the emulated drives, BUSY message will be shown on screen and serial, during this time fddEMU will not respond to input. Warning: fddEMU will not put the screen to sleep while drive is active. If there is a hardware or software problem causing an emulated drive to go continuously active, OLED screen might get damaged. <br><br>

How to use (GUI button interface)

• S1: Load Virtual Disk
• S2: Next
• S3: Previous
• S4: Open file selection Menu / Load selected file
• S5: Eject selected disk / Cancel loading file <br>

On the main screen, drive 0 "A" and -if enabled- drive 1 "B" are displayed. To use any of the functions a drive must first be selected through "S2" or "S3" buttons.<br> After a drive is selected:<br> "S1" button: in main status screen, if virtual disk is enabled, loads the virtual disk to selected drive.<br> "S2" button: in main status screen selects drive down, in file selection menu se