[Simh] MAME and simh

[Johnny Billquist]

Just a couple of comments...

On 2020-07-02 13:16, Peter Allan wrote:
> Well my request for help getting MAME to talk to simh has generated a 
> lot of replies, so let me deal with them in groups.
> 
>  > Why not use PuTTY for the VT emulator?
>  >What is the point of trying to use MAME for VT emulation?
> 
> My reason for being interested in using MAME is that it is NOT a 
> terminal emulator program All terminal emulator programs such as PuTTY, 
> xterm, SecureCRT, etc, are pieces of software that aim to emulate the 
> functions of a particular type of terminal. While all of them are useful 
> (I use putty and xterm quite a lot myself), all of them fail to 
> implement some features of the physical terminal. Usually this is not a 
> problem, but occasionally I find it really annoying. The point about 
> MAME is that, rather like simh itself, it simulates the hardware and 
> runs the real firmware from real VTxxx ROMs. In the case of the VT 
> terminal configuration, MAME simulates an 8085 microprocessor and 
> executes the code from the original ROMs. Hence all the features of a 
> physical terminal should be present automatically.

I can understand the need/interest/fun of running the actual firmware 
instead of some emulation. But of course you then have the question of 
how accurately that hardware emulation is. It's more than just a 
question of emulating the CPU that is inside the terminal. DEC was doing 
some pretty nifty things in hardware to allow some features to work.
You really should check out of smooth scrolling on the VT100 is 
accomplished... 
(http://www.bitsavers.org/pdf/dec/terminal/vt100/EK-VT100-TM-003_VT100_Technical_Manual_Jul82.pdf, 
page 4-97, section 4.7.9 - "Split Screen Smooth Scrolling". Emulating 
those hardware tricks are not going to be easy...

Anyway, to also point out something else, the VT100 have an 8080. The 
VT220 have an 8051, while the VT240 have a T11 as the main processor, 
and an 8085 for the video logic.

This should tell you a little bit about the futility of trying to run 
the wrong ROMs on the emulator...

As for getting MAME to talk to simh, I think you need to start with just 
MAME playing a terminal at all. Once you accomplish that, then you can 
start looking at how to hook them up. If the VT simulation in MAME was 
fully accurate, you would have a serial connector on the back, which the 
terminal uses. So then you need to run a cable to a serial port used by 
simh. But of course, you probably do not want an emulation down to that 
level, but are expecting to simulate the serial ports...

   Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol