gsport/src/atbridge/notes.txt

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AppleTalk Emulation and Bridging for GSport
Peter Neubauer, March 2014
Introduction
============
The Apple IIgs shipped with a fantastic but often overlooked feature -- AppleTalk networking. AppleTalk is a low-cost, easy-to-maintain network technology that
enables network booting, file sharing, and printer sharing between your Apple IIgs, Workstation Card equipped Apple IIe, and classic Macintosh machines. As of
March 2014, GSport is the first modern emulator with support for AppleTalk. Now, you can just "drag and drop" files between your machines without thinking about
disk images, FTP, or serial cables. You can develop new software with an emulator and test on real hardware. You don't need to think much about version control.
Rather, you can update the file once on your file server, and all of your emulated and real machines have the new file. You can download the latest Apple II
software and immediately run it.
Using It
========
First, you need an AppleShare-compatible file server. A classic Mac or "netatalk" server could provide this function. For simplicity, I recommend Ivan Drucker's
A2SERVER (http://appleii.ivanx.com/a2server/), which is a pre-configured and easy-to-use package with "netatalk" and other useful tools. You may run A2SERVER in
a VirtualBox virtual machine, on an existing Linux server, or on a Raspberry Pi.
Second, you need GSport 0.3 or later with ROM03 running on a Windows or Linux (x86 or Raspberry Pi) machine. Start GSport and press F4 to access the configuration
menu. If necessary, select a ROM03 image. Select the "Ethernet Card Configuration" menu option. Change "AppleTalk Bridging" to "On". Change "Use Interface
Number" to select the network where you have attached your AppleShare server or A2SERVER. Exit the GSport configuration menu.
Third, party like it is 1989. Your GS is now connected to the AppleTalk network. Refer to Apple's documentation included with GS/OS System 5 and 6 for further
directions.
Internal Overview
=================
GSport with AppleTalk networking is functionally equivalent to a real Apple IIgs with a LocalTalk/EtherTalk bridge. Originally, AppleTalk employed the "LocalTalk"
physical layer, which requires special hardware not found on modern computers. GSport converts LocalTalk to EtherTalk, a somewhat more modern physical layer using
familiar Ethernet cabling. Internally, GSport emulates the Zilog SCC chip in the IIgs, communicates with unmodified Apple-provided networking software built-in to
the IIgs and GS/OS, and converts the network traffic to EtherTalk.
Limitations
===========
- A wireless network may not work because many wireless adapters drop EtherTalk packets. Instead, use a wired Ethernet connection.
- AppleTalk bridging has been tested with System 6.0.1 and System 5.0.2 on ROM03. Booting from a local disk or from the network works. Other ROM revisions and
system software may not work.
- The SCC baud rate is incorrect because the SCC does not emulate line coding. Still, emulated network speed should be close to the 230.4kbps speed of a real
LocalTalk network.
- The bridge supports Windows using Visual Studio, Cygwin, and Linux (x86 and Raspberry Pi). Other platforms should be straightforward, but I do not have a suitable
build environment.
- The bridge requires a router on the network. The bridge should work in both a routerless and router-filled network.
- The bridge works with simple networks consisting of a single network on a single segment with a single zone. The bridge should function with all valid network
configurations and hardware routers. Other configurations might not work, and I welcome reports.
- The bridge implements the non-extended method for acquiring the network number. Interoperability would likely be better using the extended method, but this method
is much more complex.
Credits
=======
Thanks to Gursharan Sidhu, Richard Andrews, and Alan Oppenheimer for creating and documenting AppleTalk.
Thanks to Kent Dickey and the GSport contributors for GSport and the original SCC emulation.
Thanks to David Schmenk for testing, encouragement, and Raspberry Pi support.
Thanks to Ivan Drucker for A2SERVER.
Thanks to the Gus emulator engineers for showing that AppleTalk emulation is possible.
Thanks to James Littlejohn for discussions about extending the capabilities of the Apple IIgs.