Coming back to earth somewhat...
bbraun wrote:There are still SDLC capable SCCs available out there. I've looked at trying to make an interface board with one for an rpi or beaglebone black or something.
Just out of curiosity I did the obvious Google and found that there are several companies out there that sell SDLC -> USB serial dongles. The common thing about them unfortunately is that they are *hideously* expensive. ($400+ is typical; it seems like the main use for them is talking to IBM mainframes.) If it wasn't for that I'd suggest that what might be the most useful thing to do with this project would be to target the cheapest available dongle and try resurrecting the Localtalk-related code that used to be part of Linux back in the Kernel 2.0 days. (Linux used to have support for the old "COPS" ISA cards, and in fact there used to be a howto document in the kernel documentation on how to use a Linux box to do both Appletalk routing and TCP/IP encapsulation.) If that software could be fixed then you'd be able to use any old Linux box (Raspberry Pi, home NAS server, whatever) to do the job...
(If you could abstract everything into usermode instead of the kernel, using USBlib and tap/tun interfaces, then in principle you could also make the packet routing functions work on OS X as well. Then you'd only need a small Linux VM running Netatalk 2.x set up to mount and re-broadcast your network volumes to get the old old doorstops talking with the modern world.)
But $400 is seriously ridonkulous. The dongles seem to uniformly use FPGAs to do the work while you can still buy a Z85C30 from Digikey for $6.85 and a PIC (or other) microcontroller with "full speed USB" is around $10. That looks like a minimum unit price, factoring in a PC board of around, what, $40?, for a homemade Localtalk-USB converter. That's not as cheap as some people might like but considering the "universal applicability" of such a dingus might that be a better bet then trying to interface an SCC directly to the GPIO ports on a Raspberry/Beagleboard/whatever?
(It looks like there's, what, 17? easily accessible GPIO pins on a Raspberry Pi, with some of them semi-dedicated for specific functions? Looking at the Z85c30's datasheet 17 is exactly how many lines there are on the "system bus" side of the chip. Unless there's another SCC that has a more friendly-to-modern-stuff bus structure...)
This does make me wonder what's inside those Appletalk-Ethertalk bridges. Is it a single custom IC or are they an SCC, Ethernet chip, and MCU bought in bulk and crammed together? I guess it does look like you can get Ethernet modules for Arduino for "shockingly cheap", so maybe that's not that unreasonable. An AVR+Arduino ethernet module+SCC chip might almost be cobble-together-able for around that same $40 price point. The difference is that you have to do all your protocol translation in the MCU you cram in there, while making a USB-SCC peripheral would let some "bigger iron" handle that part.
Anyway, blawblaw, yacketyschmackety.