[Simh] Problem using a real VT terminal with simh

[khandy21yo]

I'd suspect  a problem with the 8th bit being handled funny , maybe mark parity Are the characters in the right pattern to be vms prompts, and are they always the same? 
If you can log  into linux fine on that terminal, telnet from there Into the emulator and see what happens. You can telnet in via cup or set the dh lines to be telnet ports.



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-------- Original message --------From: Peter Allan <petermallan at gmail.com> Date: 12/5/17  1:38 PM  (GMT-07:00) To: Mark Pizzolato <Mark at infocomm.com>, simh at trailing-edge.com Subject: Re: [Simh] Problem using a real VT terminal with simh 
Thanks to everyone for their quick responses.
To my surprise, Xon/Xoff was turned off on the VAX, specifically, SHOW TERM TTA0 showed No HostSync. However SET TERM/PERM/HOSTSYNC TTA0 made no difference.
I have tried setting the line speed to 2400, but that only slows down the output. It still contains the same characters, to the extent that I can tell. 
I will continue to experiment and I will try using a different computer so that the serial port hardware is (presumably) different. If I can't solve it, I will indeed create an issue on github as Mark suggests.
Cheers
Peter Allan

On 5 December 2017 at 19:30, Mark Pizzolato <Mark at infocomm.com> wrote:
On Tuesday, December 5, 2017 at 10:08 AM, Paul Koning wrote:

> Do you have flow control (Xon/Xoff) enabled both on the terminal and on the

> VAX?

>

> You might try a slower speed to see if that makes a difference.  It shouldn't,

> but it might give more information.

>

> Is autobaud enabled on the line?  You might turn that off and set the speed

> and related parameters explicitly.



These are all great suggestions.  Autobaud should definitely be turned off on

the VMS side, but I don't think that is the problem since he's able to login

and the commands he types produce output, which merely is garbled.



A slower speed, which is explicitly stated on the ATTACH command might

help.

     sim> ATTACH DZ LINE=0,CONNECT=SER0;2400-8N1



I think that what you're seeing is output from the simulator overrunning

the host OS provided interface to the serial port.  This came up a while back.

The simulator serial port interface delivers data to the host OS driver one

character at a time as it is emitted by the simulator.  The simulator is

notified of I/O completion when the host OS said the IO was complete.

On some operating systems, this completion notification merely indicated

that the data had made it to a kernel buffer and not actually out through

the hardware.  This early completion indication then was passed back

through the simulator and more data was then emitted.  Ultimately it seemed

that there was not a reliable way to know that the data has actually, not only

made it to the hardware, but actually been transmitted.  Some relatively

common serial ports have an output buffer in the hardware that will take

a number of characters to be transmitted as quickly as the host puts them

into the hardware, and then deliver it outbound after the fact.  In any case

due to the problem of not getting a precise indication from the OS driver of

when the data actually made it out the serial port, an alternative approach

was taken.  This approach attempts to time the delivery of character I/O

data to the OS driver by explicitly scheduling the I/O completion time based

on the port specified speed.  This approach presumes that the OS actually

starts to send some of the data to the serial port when it is presented and

doesn't hold off until some buffer full condition is achieved.



If the above ATTACH suggestion doesn't work for you, please create an issue

at https://github.com/simh/simh/issues and we can try to dig into this further.



> > On Dec 5, 2017, at 12:56 PM, Peter Allan <petermallan at gmail.com> wrote:

> >

> > I am trying to get a real VT420 terminal working with a simulated micro VAX

> 3900. However, I am having problems getting text displayed on the screen of

> the VT420.

> > ...

> > Once the microVAX has booted, if I hit Enter on the VT420, then I can see

> that a login process starts on the simulated microVAX, but all I see on the

> screen of the VT420 is a few garbage characters. Despite that, when I type a

> username and a password, I do get logged into the simulated microVAX. Any

> commands that I type on the keyboard of the VT420 appears on the screen of

> the VT420 (except the password, of course), but anything that the microVAX is

> sending to the VT420 appears as garbage. There are recognisable characters,

> but if I TYPE a file, even a small one, what appears seems to be every 7th

> character from the file starting with the first character. The output of

> commands such as DIR appear to have the same problem. ...

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