On Tue, Apr 12, 2016 at 5:41 PM, Rodney Brown <[email protected]> wrote:
> None of the terminal emulators could send a BREAK under DosBox. I think > that a BREAK needs to be synthesized, so DosBox > recognizing the UART behavior and converting it into a Telnet Break > command (RFC 854 (IAC, BRK == bytes 255, 243)) may be > challenging. Adding a DosBox keyboard command to send a Break when > connected by Telnet should be easy. > Hang on -- BREAK is not in the old USASCII 7 bit map. As explained in RFC 854, it was a >>key<< on the old Teletype ASR33 (and the ATTEN key on the IBM 2741). What BREAK did was sent a very long (i.e. 1 second if I remember correctly) "marking" time signal. Most UARTS were set up to recognize this as an "out of band" signal tell the OS to do something special. You are correct that a number of OS, would use a >>combination<< of BREAK followed by some defined pattern to try to auto-detect the speed. Sometimes when in auto detect, you just send t break repeatedly until what was being displayed on the screen matched something valid. Anyway the problem is how to >>send<< a BREAK if its not a special key. The standard way this has been handled it drop the BAUD rate to be as slow as possible (50 baud) and send an ASCII @ Assuming 50 baud is not being used, then it will look like a BREAK to the UART on the other side. [Open up the code for UUCP's uucico program if you want an example of how this done -- Warren has the sources to V7 UNIX on his site] One other question/thought. I can not speak for DOSBOX, but I know VMware does supports sending a BREAK. It will send a break from the host keyboard to the VM using the GUI. That said, I know the issue you are caught with is you want the application AdvanceLink/Kermit et al, to send a BREAK down the virtual serial line (telnet). The question is what does DOS with the BREAK when it gets it (I'm not he road so I can not look at my handy of the MSDOS encyclopedia). Assume DOS does not "eat" the BREAK but some how passes it to the application, then I think the pieces are there for the application. Clem
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