I'm interested in this, but I've got a couple other projects to work through first. The PS2 to pre-ADB & ADB adapter PCBs are supposed to arrive today, and after that I've been thinking of reviving the 030 PDS project. This is on the list, just hasn't been gotten to yet. If someone else wants to tackle it, I'd be happy to do what I can to help. This opens up all kinds of possibilities, since localtalk is pretty much the most common, fastest, external bus available on virtually all machines. With proper software, you can use it for so much more than just file sharing or IP routing.
My thought on the easiest, meaning most likely to actually happen, route to making this work is to use a z85C30 derivative that's still available. Mouser at least still sells compatible parts for about $10 in quantities of 1. Software bitbanging of the SDLC link layer through a generic RS422 interface would be tedious. Not impossible, but personally I don't see that being a very efficient or effective approach, particularly when you can get it done in mac compatible hardware for $10. Then, bitbanging the z85C30-derivative using an rpi or beaglebone black's GPIO lines seems fairly doable. I am concerned the RPI doesn't have enough GPIOs to actually talk to the z85C30, so a beaglebone black may be more reasonable. The other problem is the z85c30 is a 5V part, and neither the rpi or bbb are 5V tolerant, so voltage level conversion is necessary.
My thought would be to first create a "shield" or "cape" PCB for the desired board, which has level converters and the z85c30 part on it. Then work through Linux drivers for it to show up similar to the ISA localtalk cards.
My thought on the easiest, meaning most likely to actually happen, route to making this work is to use a z85C30 derivative that's still available. Mouser at least still sells compatible parts for about $10 in quantities of 1. Software bitbanging of the SDLC link layer through a generic RS422 interface would be tedious. Not impossible, but personally I don't see that being a very efficient or effective approach, particularly when you can get it done in mac compatible hardware for $10. Then, bitbanging the z85C30-derivative using an rpi or beaglebone black's GPIO lines seems fairly doable. I am concerned the RPI doesn't have enough GPIOs to actually talk to the z85C30, so a beaglebone black may be more reasonable. The other problem is the z85c30 is a 5V part, and neither the rpi or bbb are 5V tolerant, so voltage level conversion is necessary.
My thought would be to first create a "shield" or "cape" PCB for the desired board, which has level converters and the z85c30 part on it. Then work through Linux drivers for it to show up similar to the ISA localtalk cards.