[Simh] DEC Pro 350 Emulator

[Paul Koning]

> On Jun 4, 2016, at 11:24 AM, Johnny Billquist <bqt at softjar.se> wrote:
> 
> I'm not sure exactly which chip is on the controller itself, but that's not really so relevant. You do not talk directly to the chip anyway. The Pro controller is called DECNA, and it has it's own programming interface. But documentation for it exist, so it's mostly a question of someone taking the time to implement it.

The chip is an Intel 82586, which is a horribly bad design using queues to give descriptors to the device, misdesigned so that sometimes you'd give a descriptor to it just as it thinks it has nothing left to do so it ends up with an entry on the queue that it isn't processing.  (This is a design error that Dijkstra identified, described, and solved, nearly 20 years earlier.)

Yes, the DECNA is a whole card with more stuff on it, but you're still talking directly to the 82586.  The way the CNA works is that it implements a dual port memory on-card, visible from the Pro bus.  You program the 82586 to do its thing to/from that memory, and access the packets from host software by looking at that chunk of address space.  It doesn't seem all that hard.  The 82586 data sheet is available online, and the DECNA is documented in the Pro technical manual (on Bitsavers).  I've also seen an 82586 driver in C in some Unix version somewhere (BSD 2.11???).

	paul