[Simh] Simulating a GT40

[Mark Pizzolato]

On Monday, September 3, 2018 at 12:22 AM, Lars Brinkhoff wrote:
> I'd like to set up SIMH to simulate a GT40 as closely as possible.  To be precise,
> the GT40 that was a the MIT AI Lab.
> 
> So far, I have this:
> 
> set cpu 11/05
> set cpu 16k
> set dli enabled
> set dli lines=2
> set vt enabled
> set vt crt=vr14
> 
> First, according to the bootstrap ROM, there is a DL11 at address 175610.  I get
> this with "set dli lines=2".  However, I'm not sure I need two of them.  I tried
> "set dli address=175610", but then I got:
> Non-existent parameter.  Am I not supposed to be able to set the base
> address?

You are supposed to be able to set the base address.  There was a bug in the 
DLI device's MTAB array that wasn't set correctly.  This is now fixed.  Don't forget 
to also set the vector to the appropriate value.  

To avoid strange entanglements with the normal AUTOCONFIGURE device
address and vector assignments, be sure to enable and disable all the devices
you plan to have in your system BEFORE you manually set any ADDRESSes
or VECTORs.

> Second, is there a way to load a ROM image at address 166000?  The bootstrap
> listing says this is where it's supposed to be.  The ROM makes the GT40 works
> as an ASCII terminal, but has a way to enter a mode where it will load a
> program sent from the host.  I'd like to be able to use this mode.

Was this code really present in ROM in that system?  If so the ROM was part
of a ROM card installed in the system.  The PDP11 simulator doesn't currently 
have support for such a card and adding it would be non trivial due to how 
memory is addressed/referenced in the simulator code.   Meanwhile this
certainly could easily solved by setting the RAM in the system to 64K and 
merely loading the ROM data into the appropriate address range.  This 
would require that the current ROM data you've got be reformatted to 
adhere to the data format required by the PDP11 specific LOAD command
implemented in pdp11_sys.c/sim_load().  Comments above that routine
describe the required data layout.

Was this ROM's contents something shipped with the GT40, or was it 
unique to the MIT AI lab?  If it was a standard part, once you get the ROM data
reformatted, we can build in a way to have an automatic configuration which 
boots into GT40 terminal mode.

- Mark