[HECnet] SIMH VAX Project

[Johnny Billquist]

On 2011-07-03 11.14, Mark Benson wrote:

On 2 Jul 2011, at 14:19, Johnny Billquist wrote:

Curiousity is good. The thing you emulate is the thing that is visible at the disk contoller layer. So anything beyond that will (probably) be different from the thing you emulate. When you emulate a uVAX with an RA92 disk, simh will present you with a emulated KDA-50, on which there appears to be an RA92 connected. In the real world, the KDA-50 runs some sort of microcode, and communicates with the disk over SDI, which is a serial protocol using four coaxial cables. And the SDI protocol defines how the KDA-50 gets the RA92 to do all kind of operations.

One of these days I want to have a good look at a real VAX, they are such a departure from anything I've used :) Interesting that they use a serial disk communication system - where've I seen that crop up recently? ;)

Yeah, SATA and SAS is just really DECs SDI warmed over, except DEC did it 30 years ago, and did it better. SDI was the low level between disk and controller. The controller in turn talked a very low-level agnostic protocol called MSCP that was designed to handle all kind of disks in the same way, with command queuing, reordering, possible bad block handling for disks that didn't do that, and I don't even know what else. Controllers that talk MSCP to the computer were implemented that has SDI as the back end, but also there are also those with MFM, SCSI, DSSI, CI, networks and probably some other interface used as the low level connection to disks as well. But all that is totally hidden from the computer, who only understands MSCP.


But none of that is emulated, and there is no real point in emulating it.

So essentially you are only emulating the minimum needed to keep the VAX microcode and after that OS happy and working 100%.

Not even that. Why emulate the VAX microcode? Instead you emulate the VAX instructions, with your own "microcode" that does not look like the microcode of any existing VAX, but which works best for the platform where you are running your emulator. Programs running on the VAX are not aware of the microcode either.
(Maybe you are confusing microcode with machine code?)

Good to hear things are working now.
As for telnet vs. ssh. Well, ssh is safer, in that people can't sniff passwords easily over the network. If you worry about people doing that, then you might want to not use it. However, if your network is secure, then telnet isn't really an issue.

Inside my own network that's not an issue. Accessing it from the internet, not such a good idea. I can SSH the NetBSD   side though so I may just settle with using the 'local terminal' via screen and ssh when using the internet.

So, you just block telnet traffic from the rest of the world in a firewall, so that you need to ssh to an intermediate box you have control of, and then you can telnet from there to the simh VAX. Good enough.

	Johnny