[simh] RSTS processor identification

The Pro hard disk driver is indeed pretty simple. Nothing like DDCMP; it's more like an old style disk controller with CSRs to tell the device what to do. Basically, you convert linear sector number to cylinder/track/sector (which requires knowing the specific drive type), then load that into the CSRs along with a command. Then for a write operation you write the words of data, 256 of them, to the data buffer CSR. For a read, you wait for the data ready interrupt, then read the data one word at a time from that same CSR. Repeat for the next sector. The floppy is similar except that the transfer is byte-at-a-time, and the address mapping is more complicated because the software has to deal with the sector interleave, track skew, and funny cylinder numbering. An entirely different odd design is the Pro Ethernet card, which uses the evil 82568 Ethernet chip. That does DMA -- into a 64kW memory that's part of the DECNA card. So the OS would allocate Ethernet buffers to that memory space and can then do DMA. That's not too bad, and 64kW is a decent amount of memory. The real problem is that the 82568 is by far the worst DMA engine design ever created. It actually implements design errors that were well understood and well documented (and solved) 20 years earlier, but such considerations never stopped Intel. The documentation clearly describes DMA operation of the CT bus on both 350 and 380 (see the Technical Manual on Bitsavers). I don't know why it was never used, I never heard any rumors about it. I don't believe the bus control uses Intel chips. The interrupt controller does, yes, which is another bad design decision but one that can be worked around adequately. The Pro 380 implements only a subset of the full interrupt controller, the parts that aren't totally absurd. I/D space is just an OS issue; it works fine in the 380. As for a VT terminal, it's actually reasonably good at that but not great; the video can't quite do the full VT220 video. paul