Help with Flow Control with VAX 11/780

[Casey Leedom]

| From: markh at squirrel.LABS.TEK.COM (Mark Henderson)
| 
| I'm trying to get a bunch of UDS V.3225 modems hooked up to a VAX 11/780
| running 4.3BSD. It seems like the Vax doesn't support RTS/CTS flow control.
| Since I want the serial port speed fixed at 19200 (users dial in with modems
| ranging from 1200 bps V.22 to V.32), decent flow control is essential.
| 
| XON/XOFF is, of course, less than ideal for binary file transfers, people
| who use programs who (at least by default) need to send ^S and ^Q
| (gnu emacs, but then they can rebind their keys).
| ...
| Anyway, what I need to know is there any way I can get RTS/CTS flow control
| to work on between the V.3225's and the VAX?

  I've looked at this problem extensively.  4.3BSD does not perform RTS/CTS
flow control.  To implement it would require a new ioctl to control turning
it on and off (already added to 4.3-Reno), changes in the general tty code
to control RTS instead of sending STOPC and STARTC and changes in each of the
tty device drivers to respond to CTS and provide RTS control points for the
general driver.  All in all, really not that hard.

  However, one thing that may get in your way is the hardware itself.  For
instance we have an old ABLE DMZ/32N (a DMF32 emulator.)  It doesn't fully
support RTS and CTS.  And even if it does support it, it may support it
non-optimally.  Optimally, you'd like to simply tell the device to perform
RTS/CTS flow control itself and let the hardware take care of the problem.

Casey

P.S.  We have exactly the same problem.  We've decided to go with a
    Xylogics Annex IIe terminal server to deal with the problem.  It has
    hardware flow control as well as a host of other features that we
    need/want, it's cheap and it provides a logical separation of function
    (i.e. we don't have a Vax being used as a terminal server and if we
    ever upgrade the Vax to something bigger/better we haven't wasted an
    investment in expensive tty driver hardware.)