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Decserver 200 with Raspberry Pi host

silver2k

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Joined
Feb 13, 2023
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22
Hi everyone! I recently visited Large Scale Systems Museum near Pittsburgh and Dave showed me a pretty neat setup to network various serial devices (terminals, PDPs, etc) together using a DECserver. He gave me some pointers and between his advice and combined these instructions here https://retrocmp.com/how-tos/connecting-a-decserver-to-linux I was able to resurrect one I picked up from ebay

Here is some advice/clarification/guidance for things that tripped me up.

Buying a DECserver 200 and equipment:

1. there are 2 kinds of DECserver 200, 1 that has the 8 DB25 (MC) and 1 that has a breakout box to 8 MMJ (DL)...other than the interface cable the setup should be identical. I got the MMJ one because the one I found actually had a proper case on it.
2. If you get the MMJ (DL) version, a 36 pin to 36 pin parallel cable is needed, I used a Centronics P-4006
2. You will need a 10 pin adapter for the ethernet, plenty are on ebay if you search AUI rj45...I used a centrecom one
3. The Decserver does not store its firmware but pulls from the network. I am using a raspberry pi 4 with 32 bit OS to host the firmware. I keep it on the same switch. The DECserver doesn't get an IP and cannot be routed so it must be on the same local network as the firmware host.

Setup of the DECserver:

This is pretty straight forward.

Check your fans...both of mine were dead. I replaced them with Noctua NF-A8 FLXs and simply cut off the old connectors and soldered DEC red to fan red and DEC blue to fan black

Plug your terminal (in my case a VT102) into port 1

There is no power switch on the DECserver, it is always on if plugged in. For the first time when plugging it in hold the red button which will reset to factory settings (important as you won't know what baud or rs-232 settings it may have). Stock will be 9600.

If you have all of this correct, you will see the DECserver start on your terminal and attempt to load an image and timeout.

Local -901- Initializing DECserver "[your hardware address here]" -- ROM XXX, H/W Rev X.X
Local -902- Waiting for image load
Local -912- Load Failure, timeout


Setup of the firmware host:

This is the area that I had to do the most work figuring out and troubleshooting.

Make sure the raspberry pi is connected via ethernet locally (such as on same switch) with the DECserver.

On your raspberry pi:
1. Install mopd. There are a few packages out there and I spent a lot of time with one that would not compile. This is the one that worked for me. https://github.com/dreamlayers/netbsd-mopd You will need to compile with "make -f Makefile.linux"
2. Install tftpd. I was able to do this with a "sudo apt install tftp"
3. You will need a firmware file for the Decserver. These can be found using google...if you are stuck let me know. The firmware will need to be placed in the subfolder mopd is hosting such as /var/tftp/mod/ /tftpboot/mod/ /tftroot/mod/
4. Multicast will need to be enabled on the ethernet port. I use the command "sudo ifconfig eth0 allmulti"
5. To start the server "sudo /bin/netbsd-mopd/mopd/mopd -d eth0" (note that is the full path to where I installed mopd, yours may be different)

Make sure mopd is running and plug in your DECserver's power, you should see it load the firmware and communicate out through port 1. Once the image, is loaded you will have to press enter a couple of times to get the login prompt.

On the raspberry pi terminal running mopd, you should see the hardware address of the DECserver as it communicates. If you do not see this, there is a problem with mopd or your connection (or multicast is not enable).
If you do see the DECserver address but the DECserver is saying timeout on loading, there is a problem with tftpd - make sure you have the right firmware in the right directories.

A big thank you to Dave at Large Scale Systems Museum - https://www.mact.io/
 

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silver2k

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Also if anyone is curious what a DECserver looks like on a modern Ubiquiti network.....(I did manually name it). No IP address, just a hardware address for LAT. Also this is the first device on my network rated E (10MB/s)
 

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GreyHairedDECfan

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Dec 5, 2021
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126
Location
Northern Maryland
Also if anyone is curious what a DECserver looks like on a modern Ubiquiti network.....(I did manually name it). No IP address, just a hardware address for LAT. Also this is the first device on my network rated E (10MB/s)
I have a device named DECserver on my network as well. It runs RT-11 under simh and a media server. Didn't know there was a real hardware thing with that name!
 

tradde

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Apr 30, 2003
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Katy, Tx
I have something which I believe is similar to this. It's a Black Box Terminal server. It was made by the Black Box Corporation. It supports 16 terminal connections via DB25. I believe it has 10Base2, 10Base-T, and AUI connections to the host. I tried a few times to see if it works. I forget if I got very far. At the time I probably had no terminals to use with it. I have the "online" documents for it. It is an interesting thing. Just don't have much use for it.
 

GreyHairedDECfan

Experienced Member
Joined
Dec 5, 2021
Messages
126
Location
Northern Maryland
I have something which I believe is similar to this. It's a Black Box Terminal server. It was made by the Black Box Corporation. It supports 16 terminal connections via DB25. I believe it has 10Base2, 10Base-T, and AUI connections to the host. I tried a few times to see if it works. I forget if I got very far. At the time I probably had no terminals to use with it. I have the "online" documents for it. It is an interesting thing. Just don't have much use for it.
We had one of those at work, used it for printer sharing. For what it was it worked very well (at the time, Windows 3.0). Multiple users could send plots to a plotter and the Black Box device would switch between jobs (PCs) and correctly send plots to the single plotter.
 

silver2k

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Feb 13, 2023
Messages
22
I did the same but with a DECServer 100. Don’t recall that I had to install tftpd. As far as I understand the DECServer only use mop to load the image not tftp.

https://github.com/MattisLind/mopd/tree/master/decserver

mopd was originally created by Mats O. Jansson at Stacken computer club in Stockholm. I made some fixes to make it compile on Linux.
Thanks! I went with tftpd because the directory you put it in is named in that structure…I haven’t tested it out.

I tried one where it said the person made some fixes to compile in Linux, but I kept getting compile/linking errors due to multiple definitions of the same class.
I have a device named DECserver on my network as well. It runs RT-11 under simh and a media server. Didn't know there was a real hardware thing with that name!
It’s a handy thing for a period correct device to clean up multiple devices and multiple terminals. It saves me from having to plug and unplug various cables switching between my Vt-102 and PiDP-8, PiDP-11, PDP-11, and hopefully soon to be PiDP-10.
 

silver2k

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Feb 13, 2023
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22
Ok I spent some more time with it today and set it up to interface with my PiDP-11, PiDP-8 and PDP-11

To setup the DECserver, this guide worked really well:

To setup the services it is very well described under the section titled "Reverse LAT"

Before tinkering around with settings, I recommend backing up your firmware file so you can easily restore if something goes wrong.

The help command is very useful and will basically be your manual. I could not find a good manual for admin software setup of the DECserver, only the hardware setup, a troubleshooting guide and a normal user manual.

Follow the link above and when complete connecting is as simple as "connect [service identification name]"
When you are done, break or control+break to exit
the "disconnect" command terminates the session

Something to note (as somewhat described in the HELP files):
To change settings there is "define" and "set":
"define" permanently assigns that setting, however you need to reboot the DECserver to take effect. Use the "initialize" command to reboot or hard power cycle
"set" changes the settings for that specific session -- so if you want to make a setting change permanently and for this session you need to enter commands 2x, once for define and once for set

One thing I could use some help on is setting up my raspberry pi to automatically run the mopd command:
'sudo /bin/netbsd-mopd/mopd/mopd -d eth0'

Right now I am ssh'ing into it and manually running it when I reboot the DECserver. I tried putting this in rc.local but it didn't work, it hung the boot (I think its because the motd command steals focus). Any ideas? Sorry, I am not very strong in linux.
 
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