MUSS Source Code Now Available

I have received qualified permission to publish the MUSS source code that was recently recovered, as free and open source software. It is available here.

I have also made a bit of progress on the MUSS restoration. My implementation of FLIP is improved but still not quite there yet. I also have a parser for MUSL, which parses the output of my FLIP implementation for one of the FLIP source modules, with a little hand modification before parsing it.

I have created a page on MUSS where I will report more about MUSS and its restoration.

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I have now got a crude implementation of the Flocoder Flip program written using Flex and Bison. It can take a Flocoder file from the MUSS sources and extract what I hope is compilable MUSL code. The code is on GitHub.

I am not 100% sure that the code is valid as I have taken a very naïve approach to the code generation stage. Every BOX except the start box is labelled, and every BOX ends with a jump to the next box in the FLOW sequence. It does not attempt to merge consecutive BOXes.

However, I am hoping that this is enough to take the original Flocoder source for Flip and turn that into MUSL that I can then compile. The next step, which I have just started, is to create a MUSL to C compiler that will generate C from the Flocoder source for Flip, so I can get a version of Flip working in C. If I can do that then I should be able to process the Flocoder files using the proper code for Flip and compiling those to C as well.

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MUSS GitHub Project

For anyone who wants to follow the effort to revive MUSS, I have started a project on GitHub. You can find the repository here. The initial effort is focussed on creating FLIP to translate the Flocoder to compilable MUSL and I have made a start on that.

Once I have FLIP then I will need to start the process of compiling MUSL. I will probably compile the MUSL to C and then compile the original MUSL compiler (written in MUSL), but that is a little bit further off.

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MUSS Source Code


MUSS is the Manchester University Software System. It is an operating system that was designed and built at Manchester University for MU5, designed to be portable, and in fact ported to other machines.

In October 2017 I asked the editor of Resurrection, the Computer Conservation Society’s publication, to publish an appeal for information relating to MU5 to help my emulation project. Then, in December 2017 I received a response from Eur Ing Brian Tompsett a lecturer at Hull University. He had a full set of printed MUSS documentation and a 9-track magnetic tape which he thought may have the same documentation on it. The interesting thing about MUSS documentation is that it is really a combination of documentation and code, written using a system called Flocoder. This meant that there may be machine-readable source code on the magnetic tape. However,  Brian Tompsett thought that the tape may only contain the portable parts of the sources from the post MU5 era, covering MU6G, PDP11, VAX11 and MC68000. This also ties in with the printed documentation I have seen in a store room at Manchester, which all seems to be post MU5.

In April 2018 one of Brian Tompsett’s tapes was sent to The National Museum of Computing in Bletchley Park, where Delwyn Holroyd read the tape successfully a week ago. It contained a tar file, inside which were a large number of documentation and source code files.

The tape appears to contain the source code for Flocoder, the Manchester University system implementation language (MUSL) compiler, large parts of Version 11 of MUSS itself and other compilers, including Fortran and Cobol compilers that Brian Tompsett wrote. I am waiting for permission from Manchester University and then I hope to post the files, possibly on GitHub.

It looks like the best approach is going to be to hand build a processor to implement the Flocoder FLIP (Form LInear Program) function to extract the MUSL from the documentation, and then build a MUSL compiler, which will allow me to bootstrap the building of MUSS. It looks like it may be possible to get MUSS built for PDP-11 and VAX.

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Another DEC Rainbow 100+

I recently acquired another Rainbow 100+. Here is a picture of it:

Rainbow 100+

The badges are on their side because this was installed in a vertical enclosure.

This came about because a little while ago I was given a Rainbow, and the person who gave it to me had a second one that he was going to keep. He told me that he wanted the vertical enclosure for his machine, like the one below, which happens to be one that I passed on to someone else some time ago:

Vertical Enclosure for a DEC Rainbow

When the opportunity arose to buy a Rainbow in a vertical enclosure I let him know. He wanted the enclosure but not the machine inside. So we agreed that I would contribute to the cost of the purchase, take the Rainbow itself and he could keep the enclosure.

When I got it home it was in a pretty clean condition. It contains an RD51 hard disk, an RX50 floppy disk drive and a 192K memory expansion options, for a total of 320K memory. The VR201 is an amber version.

Before powering it on I visually checked the PSU, it looked fine. I then imaged the hard disk, just like I did with the previous Rainbow. Interestingly, the first attempt to read the disk failed completely. The disk span up quite happily, but the MFM emulator could not find any data. Cycling power seemed to fix it and I imaged it twice just to be sure.

I then installed the hard disk emulator in place of the hard disk and powered it up. Booting from the emulated hard disk brought up MS-DOS 2.11. The AUTOEXEC.BAT then took me into the Rainbow Serial Port Setup Utility (SETPORT) program. I found that the hard disk had WordStar 3.31 installed. At some point I will go back to that and remind myself what WordStar was like.

Anyway, I now have another Rainbow and another VR201 monitor, which is good in case I need some spares.

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More Leaking Batteries

I haven’t been very active lately because I have had to temporarily relocate my collection. While moving it back again I took the opportunity to reorganise things a bit. In doing so I came across the first two PC motherboards I ever bought. I found that both had leaking batteries. I have another machine, a DECstation 220 that has suffered as a result of the same kind of battery leaking, so I decided to remove these batteries immediately.

The very first motherboard I ever bought was a 286 board, with a Headland HT-12 chipset. If I remember correctly it had 1MB of memory.

The second board I ever bought was a 386SX board with an ALI chipset.

I have added these boards to the pile of things to get working. I am a bit behind at the moment with the fact, as mentioned above, of having to temporarily relocate the collection. I am still working on the TURBOchannel Extender PSU, a couple of ZX Spectrums and the DECstation 220. However, when I get a moment I will give these two boards a very quick spin just to see if they still work at all.

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Update on H7826 Power Supply Repair

It has been a while since I last posted anything about what I have been up to. However, I have been busy trying to find out what is wrong with the H7826 power supply out of my TURBOchannel Extender.

I received advice that there were errors in my method for checking activity on the primary side and that the fault could be on the primary side. I spent some time reverse engineering the schematics for the primary side. Not being an electronics engineer I may not have drawn this logically, and there will be tracing errors. I will update the images as time goes on, so by the time you read this it may have been improved, but don’t count on it. Unfortunately the part numbers are not labelled on the boards, so I have labelled photographs with part numbers that I have made up myself.

This is the schematic for the main input section.

This is the schematic for the 50-19530 daughter board, which I think is for Power Factor Correction.

This is the schematic for the 5019572 daughter board, which controls the switching transistors. This one was done by Matt Burke, I have added labels to a photo and filled in a couple of missing bits.

Further probing with an oscilloscope revealed that the 555 on the 5019572 daughter board was not oscillating, which means the switching transistors are not being switched. I then found that the Vcc input to the 555 was not rising above about 0.2V. So the next thing was to see why this might be.

Unfortunately, while doing the probing around the 555 I think I managed to discharge the large smoothing capacitors near the 555. Thankfully I had already turned the power off, but there was a sharp crack from the spark. I could not find any physical damage anywhere.

I took the 5019572 out to test it on the bench with a bench power supply. I found that it drew far too much current, the current limiter on the bench power supply happened to be set to 1.2A, and that is what it drew. Clearly there was a short. I suspected the 555, partly because of the spark problem. When I took it out I found that it was indeed shorted across Vcc and Ground.

I replaced the 555 and then I found that its output oscillated. However the current draw was still high and the other IC, the UC3842 got very hot. I checked all the resistors, diodes and capacitors for shorts and they all appeared to be fine, so I suspect the UC3842 is also bad.

I now have to order a replacement UC3842 and see if I can get the daughter board to work correctly.

I am not sure if the short (or shorts) have been caused by the spark I provoked. However, the fact that Vcc on the 555 wouldn’t go above 0.2V when the board was installed suggests it may have already been shorted, or the UC3842 was already bad, but of course I won’t know until I have the daughter board working again and installed back on the main board.

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