Building a Franken-PDP-11 out of parts?

[joev]

One day, I'd love to have a real, small PDP-11 to bang on, like an 11/05, 11/53, or LSI-11. Starting with something like this (a Mentec QBUS CPU) or this (M8191 CPU from a /23), would I "just" need a QBus backplane, power supply, some sort of QBus storage controller, and cables?

 

[cruff]

Yes, that will work, for CPUs without a serial port you will need a board that is capable of acting as the standard console port interface. You may find it useful to have an Ethernet interface also.

 

[stephenbuck]

There’s a great web page on putting together a minimal PDP-11 system here:

http://www.diane-neisius.de/pdp11/index_E.html

 

[gslick]

One day, I'd love to have a real, small PDP-11 to bang on, like an 11/05, 11/53, or LSI-11. Starting with something like this (a Mentec QBUS CPU) or this (M8191 CPU from a /23), would I "just" need a QBus backplane, power supply, some sort of QBus storage controller, and cables?

An M7554 KDJ11-D PDP-11/53 would be better than an M8191 KDF11-B PDP-11/23+ as it gives you 512KB of built-in RAM (some versions have 1.5MB), plus the split I/D capability if you wanted to run something like 2.11BSD which requires that.

For example:

www.ebay.com/itm/Digital-Equipment-Processor-KDJ11-D-DEC-M7554-CPU-Working-PDP-11-53/153730279096

An alternative to the Mentec M1 is the Quickware QED-993.

www.ebay.com/itm/QED-993-Single-Board-Q-Bus-CPU-w-cab-kit/200600166676

I can't really recommend the QED-993 because it lacks floating point support and as far as I know no one has been able to get 2.11BSD to run on it. I wasn't able to get RSTS/E 10.1 to run on it either. I have no experience with the Mentec M1. That listing says it doesn't have floating point support, so 2.11BSD might not run on it either. The Mentec M1 is too expensive for me to buy one to try out myself.

 

[bqt]

An M7554 KDJ11-D PDP-11/53 would be better than an M8191 KDF11-B PDP-11/23+ as it gives you 512KB of built-in RAM (some versions have 1.5MB), plus the split I/D capability if you wanted to run something like 2.11BSD which requires that.

For example:

www.ebay.com/itm/Digital-Equipment-Processor-KDJ11-D-DEC-M7554-CPU-Working-PDP-11-53/153730279096

An alternative to the Mentec M1 is the Quickware QED-993.

www.ebay.com/itm/QED-993-Single-Board-Q-Bus-CPU-w-cab-kit/200600166676

I can't really recommend the QED-993 because it lacks floating point support and as far as I know no one has been able to get 2.11BSD to run on it. I wasn't able to get RSTS/E 10.1 to run on it either. I have no experience with the Mentec M1. That listing says it doesn't have floating point support, so 2.11BSD might not run on it either. The Mentec M1 is too expensive for me to buy one to try out myself.

2.11BSD works fine on hardware without FP. It was fixed a few months ago, or maybe a year...

But I would still probably recommend a processor with FP, since there are more things you might want to run, that would require it.

The question is, is that QED-993 with, or without FP. It did exist, but was optional, as far as I know.

 

[gslick]

2.11BSD works fine on hardware without FP. It was fixed a few months ago, or maybe a year...

But I would still probably recommend a processor with FP, since there are more things you might want to run, that would require it.

The question is, is that QED-993 with, or without FP. It did exist, but was optional, as far as I know.

Even if 2.11BSD can now be built to work on a PDP-11 without FP support I am still skeptical that it would work on a QED-993, unless someone that has a QED-993 can actually verify that it works, and provide details on what they needed to do to get it to work.

The QED-993 is not like a KDJ11 chip which has microcode FP support when the optional FPA chip is not present, the QED-993 doesn't implement the FP instructions at all, at least that is the case with the two that I have.

As far as I know FP support was never actually released for the QED-993. Again, I would be happy to be proven wrong by someone that actually has a QED-993 with FP support. I exchanged email a couple of years ago with someone that worked at Quickware back in the day. He was able to send me some QED-993 installation manuals, and even source code for the 68360 support processor, but he wasn't able to provide any information about FP support. Too bad he didn't have source for the Xilinx FPGAs or microcode he could send me.

The installation manual I have says this:
"When configured with the daughter board for floating point instructions, the QED 993 uses a state-of-the-art high speed FPGA component assisted by microcode. This part includes a full FP register set and supports F and D data formats."

Has anyone ever seen a QED-993 with a daughter board attached to it? The QED-993 that I have came from the same seller, "icsscorp". There are no connectors present on the board where a daughter board could be attached. There are some footprints on the back of the board were maybe connectors could have been soldered.

 

[bqt]

Even if 2.11BSD can now be built to work on a PDP-11 without FP support I am still skeptical that it would work on a QED-993, unless someone that has a QED-993 can actually verify that it works, and provide details on what they needed to do to get it to work.

The QED-993 is not like a KDJ11 chip which has microcode FP support when the optional FPA chip is not present, the QED-993 doesn't implement the FP instructions at all, at least that is the case with the two that I have.

As far as I know FP support was never actually released for the QED-993. Again, I would be happy to be proven wrong by someone that actually has a QED-993 with FP support. I exchanged email a couple of years ago with someone that worked at Quickware back in the day. He was able to send me some QED-993 installation manuals, and even source code for the 68360 support processor, but he wasn't able to provide any information about FP support. Too bad he didn't have source for the Xilinx FPGAs or microcode he could send me.

The installation manual I have says this:
"When configured with the daughter board for floating point instructions, the QED 993 uses a state-of-the-art high speed FPGA component assisted by microcode. This part includes a full FP register set and supports F and D data formats."

Has anyone ever seen a QED-993 with a daughter board attached to it? The QED-993 that I have came from the same seller, "icsscorp". There are no connectors present on the board where a daughter board could be attached. There are some footprints on the back of the board were maybe connectors could have been soldered.

The part about FP support on the QED-993 existing, but being optional was something I read from Quickware. I would assume they know, but I have never played with the CPU, so I don't know.

2.11BSD have been used on an FPGA implementation of the PDP-11, which is why the FPP support in 2.11BSD was fixed. That FPGA definitely do not have any FPP.

 

[gslick]

The part about FP support on the QED-993 existing, but being optional was something I read from Quickware. I would assume they know, but I have never played with the CPU, so I don't know.

2.11BSD have been used on an FPGA implementation of the PDP-11, which is why the FPP support in 2.11BSD was fixed. That FPGA definitely do not have any FPP.

Is there a 2.11BSD patch related to FP support more recent than patch 445 from 2006? The last time I tried to get 2.11BSD working on a QED-993 I did rebuild the kernel with patch 445 applied. That wasn't sufficient to solve the problems.

Subject: kernel floating point simulation crash, postscript printer Makefile update
Index: sys/pdp/mch_fpsim.s,local/mp/Makefile 2.11BSD

Description:
The in kernel floating point emulator, used when no hardware FP unit
is present, would panic the system on the first FP instruction
executed by a user program.

Repeat-By:
Try to run a program using FP on a system w/o hardware FP
Fix:
Apply the patch below and rebuild the kernel.

Also included in the patch is an update to the 'mp' Makefile. This
had been completed several years ago but never posted.

------------------------cut here-----------------------
*** /usr/src/sys/pdp/mch_fpsim.s.dist Sat Dec 26 23:38:19 1992
--- /usr/src/sys/pdp/mch_fpsim.s Tue Dec 26 14:56:08 2006

There might be other compatibility issues with the QED-993 beyond the lack of FP support. As mentioned previously I wasn't able to get RSTS/E 10.1 to run on the QED-993 either, even when configured for a PDP-11/23 without split-I/D and FP support.

I should start a separate thread about the QED-993 instead of derailing this thread. But in any case, I couldn't recommend a QED-993 for someone just starting in the PDP-11 world.

 

[bqt]

Is there a 2.11BSD patch related to FP support more recent than patch 445 from 2006? The last time I tried to get 2.11BSD working on a QED-993 I did rebuild the kernel with patch 445 applied. That wasn't sufficient to solve the problems.

Yes, this was fixed in patch 453, dated Oct 11. 2019. So it was more recent than I had through. I received a copy somewhat earlier, but it took time before it got officially in there.

There might be other compatibility issues with the QED-993 beyond the lack of FP support. As mentioned previously I wasn't able to get RSTS/E 10.1 to run on the QED-993 either, even when configured for a PDP-11/23 without split-I/D and FP support.

I should start a separate thread about the QED-993 instead of derailing this thread. But in any case, I couldn't recommend a QED-993 for someone just starting in the PDP-11 world.

If there are more people interested in the QED-993 I guess we should have a separate thread about it. According to Quickware it should be a drop-in replacement.
A bit curious why that would not be the case then...
Quickware is still around, so we could just ask them.