[HECnet] PDP-11/70 on FPGA

[G ran hling]

All of the interfaces "supported" are "oldish", i.e. they were implemented in TTL without any local "interface processor". Later interfaces were more or less all based on some embedded CPU to do the shuffling.

So, in taking this great work further, some suitable "soft processor hardware" needs to be implemented.

I realize there are several "commercial" alternatives, some supplied by chip vendors etc, some requiring costs, licensing etc... None of that is worthy to be a part of an open design, in my opinion...

Would it be more feasible to us in this community to use some design we already can master, and that we already have the tooling for? Should a PDP-11 be used for peripheral needs? If so, which model of the 11 should this "I/O-slave" be designed around?

Or is there already any "better" alternative (architecture so superior that it's worth learning/getting tools for) that I should put my eyes upon for this task?

A full 11/70 (for each interface) core feels just a little to much to myself. What about a 11/40 design??? Would 256 kB of (max) memory be to small to design an efficient Ethernet interface? Would the lack of separate I & D - space be to much of a problem. Or should a yet simpler design be enough. Not even implementing 18-bit MMU (thus max 64 kB of memory) should be enough to do several interfaces - just like DEC used 8080 on some boards (!?)

If such a design where used, should it be programmed upon RT-11? These "systems" should behave like embedded systems once finished, running from "PROM".

I have found a POP-11 online, that's seems to be open source, though not written in VHDL (that by the way also includes an IDE interface). Could this after all be a starting point?

I'd like to hear your thoughts on my ideas, even though I'll have to learn VHDL and get myself some hardware to get going - this is the starting-point I've been waiting for quite a while, dreaming of implementing like a 11/93-based system in FPGA. Beeing a spare-time dream, don't expect any of my dreams to come real "next week", though ;-)

/G  ran