'stty exta' for 19.2Kbaud on USG doesn't work

[P McFerrin]

I did some investigating of 19.2 on DZ11"s.  My work was done on USG 5.0.1
so if you're running something differrent, this may or not apply.

I tested several of my DZ11's to see if they would indeed work at 19.2KB.
I discovered that systems running DZ11's WITHOUT KMC11 assist will NOT work
unless a change is made in the driver (dz.c for those who have source
license).  There is an internal speed table that converts the 'standard'
baud rate values (e.g. B300, B1200, EXTA, etc) to values appropiate for
the line parameter register of the DZ11 line.  The entries for EXTA and
EXTB are zero which will set the baud rate to 50 baud.

The driver for the kmc11 assisted DZ11 (dzb.c) have a value of 017 for
both EXTA and EXTB which selects the 'NOT USED' baud rate (according to
the DZ11 Users Manual).  Data is indeed xmited at 19.2.  I ran some tests
to see if the KMC11 could keep up with this baudrate.  I started up
8 processes (each on a different line, same DZ11/KMC) that was i/o bound
(constantly writing the same buffer repeatedly).  These programs calculated
their own thruput and ALL OF THEM attained 19.2KB thruput (VAX 11/780).
The CPU was kept busy about 60-70% of the time (mostly in kernal mode).

I repeated the test on a PDP11/70 without KMC11 assist.  I could only start
3 processes and retain the 19.2 thruput.   Just one process alone caused the
the CPU to be busy 98% of the time!

We have not made any use of 19.2kb in any of our applications.  I was just
attempting to verify what I was reading on the net.  There is still the issue
of official DEC support.  The only impact (related to maintenance) I can
see that 19.2 may have is the EIA driver/receivers may be marginal for
A PARTICULAR INSTALLATION (e.g. cable type/length) that could possibly
lead to future problems that can ONLY be duplicated at 19.2KB.
In this situation, DEC probably has the right to say "we don't support the
DZ11 at 19.2".
Of the few DZ11 failures we have have, none have been related to
EIA receiver/driver problems.
There is however always the possibility that
this 'NOT USED' feature might dissappear in some future revision of the
DZ11 board.

			Paul McFerrin