Imported from GitHub: GLGPrograms/tinyDiskII · commit 982f6e1 · license GPL-3.0

Description

Homemade floppy disk emulator for Apple II series computers

README

tinyDiskII

Homemade floppy disk emulator for Apple II series computers

:warning: Work in progress: read carefully the README before trying to reproduce this project!

tinyDiskII is able to simulate an Apple Disk II both in reading and writing. Disk images are stored into a FAT16 formatted SD Card. Each disk image must be a DOS 3.3 floppy image, saved as .NIC. A cross platform .NIC <-> .DSK conversion tool will be available soon on this repository. Floppy formatting is currently not supported, but it is currently under developement.

BOM

Reference(s)	Description	Notes
C1, C2, C3, C4, C5, C6, C8, C9, C10, C11, C12	0805 100n Capacitor
D1, D2	0805 Red LED
J1	2x3 male jumper	ICSP connector
J2	SMD SD Card slot
J3	THT USB B Mini connector	Mount for USB debug
J4	2x10 male connector	DiskII connector
R5, R6	330
R2, R3, R4, R7, R8, R9, R10, R11, R12, R15	10k
R13, R14	0	Replaced with a bridge
SW1	RotaryEncoder with switch
U2	SN74LVC244	5V tolerant buffer
U3	CH340C	Mount for USB debug
U4	ATxmega16A4U-A	MCU
U5	74AHCT125	Level shifter
U7	0.96" OLED I2C	7-pin model
U10	AP1117-33	3v3 linear regulator

Do Not Place, reserved for future implementations

Reference(s)	Feature
U1	Flash/EEPROM interface
C12	"
R1	"
C13, C14	USB ESD
R13, R14	"
D3, D4	"
C7	USB self reset
J5	Debugging connector

Schematics and PCB

:warning: Schematics and PCB layout can be found in /schematics folder. Please note that I had physically implemented only rev1.0, which requires some hardware patches. The issues were fixed in rev1.1, but I never put it into production. Build it at your own risk.

Firmware

Firmware source code is in /firmware folder. Code can be compiled on a linux/wsl machine through make command. Make sure you have make and avr-gcc toolchanin installed. Output binary will be generated as /firmware/output/tinyDiskII.hex.

In /firmware/tests there are some unit tests that can run on host system. They can be compiled and executed with:

cd firmware/tests
cmake -B build .
cd build
cmake --build .
./tinyDiskII-tests

Command line linterface

The serial interface is mainly used for application logging. If no OLED display is detected, the serial interface is enabled for receiving commands. If the OLED is connected, the command interpreter is disabled to avoid conflicts.

The following table resumes the available commands.

Command	Arguments	Description
INIT	none	Initialize the SD Card (1)
CWD	dirname	Change woring directory to dirname
UP	none	Change working director to the parent directory
LST	none	List files and directory in the current working directory
SET	filename	Select filename, in current working directory, as currently inserted disk (2)
REM	none	Remove currently inserted disk
FAT	upto	Prints FAT entries of selected file up to index upto (debug)
INFO	t s	Prints .NIC file informations about sector s in track t (debug)

1. If OLED is not connected, the SD Card must be manually initialized.
2. At startup, no disk is inserted.

Changelog

• rev1.0: first version

• rev1.1: fixes the issues present in rev1.0:

  • LV_DISK_READ connected to U4 pin 21;
  • SD_WP connected to U4 pin 22;
  • SD_DETECT connected to U4 pin 23;
  • Added 10K pull-up resistor to DISK_WRITE_EN;
  • Pin 4 and 16 of U3 are shorted together.

Contributors and references

• The whole projects borns as a custom implementation of Koichi Nishida's SdiskII [1] [2], which I used as a starting point for firmware developement.
• Jörg Hagedorn made a replica of the tinyDiskII hardware rev1.1 and he found a bug in the SD sector's addressing, now fixed.
• Kamen Angelov made a replica of the tinyDiskII hardware rev1.1, he found a bug with SDHC card and he sent some fix proposal.