[Simh] More VAX Simulators

[Johnny Billquist]

On 2019-05-03 22:37, Paul Koning wrote:
> 
> 
>> On May 3, 2019, at 3:52 PM, Johnny Billquist <bqt at softjar.se> wrote:
>>
>> That came across wrong...
>>
>> Flow control would most certainly help, however, when running in a simulator, with a terminal window, connected to the system, there is actually no flow control available, so you will loose data.
> 
> Why would there be no flow control available?
> 
> Flow control is part of the protocol, no different from escape sequence parsing.  If a terminal emulation receives a control/S from the host, it should stop sending characters to the host.  For that to be meaningful, the "off" action has to happen close enough to where the characters are picked up by the driver that you don't get the simulator equivalent of "Fifo overrun" but that is not hard to arrange.
> 
> If the emulation currently doesn't do this, forcing the character rate down to "really slow" should be an adequate workaround.

Essentially, terminal emulators usually totally ignore XON/XOFF if it 
comes on a telnet session, or pty. Unix do handle XON/XOFF if you come 
in on a physical serial port, but basically not in any other 
circumstances. Terminal emulators themselves don't really try to handle 
this. Both ptys, as well as telnet (or any other tcp connection) have 
their own flow control anyhow, so there is no need, and possibly no 
point in trying to handle XON/XOFF.

This was a fun exercise I had to sort when I did telnet in RSX, as the 
normal serial port flow control isn't really helpful anyway at that 
point. Delays are just too long, not to mention that no telnet client 
would ever understand or care if I sent it an XOFF.

   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