Slower than expected baud rate over serial dz terminal set to 9600 baud

[eneilson-zz]

• Serial terminal speed through DZ lines is less than 9600 baud, even though terminals are connected at 9600.

Tested with the RSX-11 OS:
Detecting issue with Test #1:
When PiDP first starts and you enable a dz terminal at 9600 baud in boot.ini (see lines below), the connected speed runs slower until the user toggle the terminal speed between two baud settings in RSX like this:
SET /SPEED=TT3:300:300
SET /SPEED=TT3:9600:9600
After these steps, the connect speed flows at a full 9600 baud.

Test #2 (another workaround)
Another method to get the terminal flow at full 9600 is to not attach the dz terminal until the RSX OS has fully booted like this:

1. Enter all of the dz settings in boot.ini EXCEPT the attach command.
2. Once RSX is fully booted, stop PiDP with Ctrl-E and at the prompt, enter, "attach dz line=0,connect=/dev/ttyUSB0
3. Typed "cont".
4. Connect at 9600 with a terminal over serial and you will get the full 9600 bps immediately and not have to use the set speed commands.

Here are the DZ settings used in boot.ini:
set dz enable
set dz lines=8
set dz address=17760030
set dz vec=330
attach dz 10001
attach dz line=0,connect=/dev/ttyUSB0 <--This line was commented out in test #2 above and entered later.

• the output of "sim> SHOW VERSION" while running the simulator which is having the issue

DP-11 simulator V4.0-0 Current REALCONS build Aug 14 2019
Simulator Framework Capabilities:
32b data
32b addresses
Threaded Ethernet Packet transports:PCAP:TAP:UDP
Idle/Throttling support is available
Virtual Hard Disk (VHD) support
RAW disk and CD/DVD ROM support
FrontPanel API Version 12
Host Platform:
Compiler: GCC 8.3.0
Simulator Compiled as C arch: ARM (Release Build) on Aug 14 2019 at 18:18:20
Memory Access: Little Endian
Memory Pointer Size: 32 bits
Large File (>2GB) support
SDL Video support: SDL Version 2.0.9
No RegEx support for EXPECT commands
OS clock resolution: 1ms
Time taken by msleep(1): 1ms
OS: Linux pdp-11 5.10.63-v7l+ #1496 SMP Wed Dec 1 15:58:56 GMT 2021 armv7l GNU/Linux
git commit time: $Format:%aI$

• how you built the simulator or that you're using prebuilt binaries

Followed the PiDP-11 v.2 Manual for installation using binaries from https://www3.ispnet.net/pidp11/pidp11.tar.gz

• the simulator configuration file (or commands) which were used when the problem occurred.

detach all
;reset all
set tti 7b
set tto 7b

set cpu 11/70, 4M

set xu enable
;set xu address=17774510
;set xu type-delua
set xu mac=aa:00:04:00:1e:78
attach xu eth0
sho xu

; under SimH 4, "throttling" results in a disturbed "idle pattern"
set nothrottle
set noidle
;set throttle 50%
;set console telnet=10000
sho cpu

attach LPT lpt.txt

set tm disable
set hk disable
set rp disable

set rq0 autosize
attach rq0 PiDP11_DU0.dsk
set rq1 autosize
;enable this line when you want to use the DECUS disk image collection
;which comes on a separate 1.7GB disk:
attach rq1 PiDP11_DU1.dsk
set rq2 autosize
set rq3 autosize

set tq tu81

set dz enable
set dz lines=8
set dz address=17760030
set dz vec=330
attach dz 10001
attach dz line=0,connect=/dev/ttyUSB0
;attach dz line=1,connect=/dev/ttyUSB1
sho dz
;attach dz line=0,connect=/dev/ttyUSB0;speed=9600-8N1

; connect to panel
set realcons host=localhost
set realcons panel=11/70
; We're running on a desktop PC with connection to localhost: max speed!
set realcons interval=1
set realcons connected
;set realcons debug
;show realcons

boot rq0

• the expected behavior and the actual behavior

The output is slow scrolling of the serial terminal output regardless of what RSX commands you are executing.

• you may also need to provide specific pointers to data files that may be necessary to demonstrate the problem