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My Raspberry Pi Thinks It's a Mainframe!

Andrew Back
10
Open source (hardware and software!) advocate, Treasurer and Director of the Free and Open Source Silicon Foundation, organiser of Wuthering Bytes technology festival and founder of the Open Source Hardware User Group.

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November 2, 2015 12:08

Fantastic Ive worked on many mainframes 409 4331 Sytem 34/6/38 As/400 etc - Love to see them emulate AS/400as that was the last and longest contracts for me

Keep up the good work

November 25, 2014 19:18

@qubex I love that you have Hercules up and running on a Parallella board! I wonder if it could be extended to use the Epiphany cores as special I/O processors... Now that would be something.

It's funny you should ask about interfacing a real IBM terminal, as I've long wanted to do this and I believe it is possible using a 3174 controller, which can be picked up on eBay for not that much. However, you'd need to check as to which one to use, although in terms of media interfaces it would obviously need to have twinax (I imagine they all have this) and 10BaseT or similar. Then IIRC you would need a certain boot disk for the controller, that will allow you to "reverse TN3270" from the terminal and into Hercules over IP. I actually picked up two 3174s for this reason, but I'm not certain they are the correct version and haven't looked into boot floppies yet.

Of course, whenever I see all those 3270 emulation cards on eBay I can't help but wonder how hard it would be to write a Linux driver that did pretty much the same thing, albeit with Hercules on the same box and then the terminal direct attached. However, regardless of how difficult or simple that would be, it's definitely beyond me!

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May 29, 2018 07:15

@Andrew Back I'm impressed how write with the accuracy of mainframe and mini computers I'm a legacy mainframer myself and other computer architecture too. My background encompasses Mainframe,Mini, Maxi, Midi's, PC's, and SBC and microprocessors application, design and programming. Can you do a discussion on the differences between Mainframe, Maxi, Midi and Mini computers and what defines them for class. And highlight their strongest features possibly, I think that would be great for all the computer community, newbies and legacies and gurus and sages. Please huh, please can ya, please huh, say you will. Thank you for your time and editorial. Sali'Essex Adan Fores.

November 25, 2014 11:19

Hello.

I am pursuing a project very much like this one, or rather: I am using a Parallela embedded system to emulate a later, more powerful IBM mainframe. But much of the underlying logic is identical. I have a Linux distro running on the board and there’s Hercules running inside that, happy and snug and somewhat stupefied at the inordinate processing power available to it.

There is, however, a complication, or rather, a very satisfying (though perhaps somewhat confounding) addendum, which is this: I am in possession of a working, 1978-era IBM 5221 terminal with keyboard.

Now, I know that this specific terminal uses the 5220 protocol used for the IBM S/38 (and later AS/400) and not the 3200 protocol that the S/390 and successors use natively. However, it provides the opportunity for significant realism, nostalgia, and general geek cred.

My question is this: does anybody have experience interfacing a modern system with a legacy TWINAX-sporting terminal? In my mind’s eye I am imagining some kind of screen parser and poller, and then some kind of standard box that converts between 5220 over TWINAX and x- or z-modem over RS-232; and then some kind of USB-to-RS232 converter. Alternatively some gadget that provided conversion between telnet over Ethernet and 5220 over TWINAX would be equally suitable.

In short, I’m fishing for ideas… and perhaps ready-made solutions to what, I imagine, was, back in the day at least, a fairly standard problem.

Any suggestions?

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April 1, 2014 13:58

Hi Robs,

Nice project!

Like others, I'm confident that you could achieve what you want with a Raspberry Pi or similar driving a monitor. However, I think an actual physical console driven by the GPIO of such a board and with switches and incandescent lamps, or even just LEDs, would be far more interesting. And in fact this is something I've wondered about before, not with that system specifically, but in general with SimH — which can simulate a Honeywell 316, among other things — and Hercules.

Wouldn't it be fantastic if you could hook up a clone of a classic console to a small computer running Linux, and interact with the original O/S running on simulated/emulated hardware. Not just for enthusiasts and those who used to work with the actual machines many years ago, but for museums and perhaps universities also.

Cheers,

Andrew

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April 1, 2014 10:10

Robs, I agree with Boss that the lights should be doable. The actual indicators from that era were incandescent. The thermal lag of incandescent bulbs, along with the relatively slow response of the human eye, limits the effective flicker / update rate of the display. Updating the display 30 to 60 times per second should be very adequate. Each 30th/second update could output for each bit an analog brightness level corresponding to the activity on the corresponding bit over that time interval. (16 brightness levels would likely be very sufficient.)

Given that memory cycle time was one or two microseconds on the Honeywell 200 Series, you should have enough processing speed in a Raspberry Pi or modern PC to maintain a 16 bit counter for each address and data bit on the control panel, incremented once for each emulated cycle during which the corresponding bit is a "1". (2**16 > 1Mcycle * 1/30 sec) At the 30th of a second interval, divide the current value of each of the counters by the number of actual emulated memory cycles (which might be as low as one cycle if single stepping) to get the fraction of full brightness for the corresponding address or data bit indicator for that 30th of a second interval. Update the display (hardware or graphic) accordingly, and reset the counters to zero in prep for the next 1/30th second interval.

-Brad

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March 31, 2014 19:36

Hi robs, I can't prove you wrong, but I don't think that should be too difficult for someone who works with graphics as the inputs that determine the lights flickering are relatively low frequency. But I can't do it!
I did make a real-time system that used DirectX to be the synchronisation source for my whole program. It was all synced to 50Hz frame rate which read the asynchronous A/Ds, did the calculations, updated the display frame counters, updated the display etc., all in the available time slot. This was on an old PC, WinXP and DirectX6 or 7 from memory, so again I think a 'good' programmer could do something along the lines you want these days.

Your post stirred some great memories. In the early 70's the Technical College I attended installed the old Town Hall computer for use by the students. Can't recall the make/model but it had some great features, the 'engineers' panel was great, with its clunky push buttons, large side on rotary pots and a loud speaker to listen to bus faults or program errors. You could also raise and lower the logic supply voltages to identify 'future' errors that may cause problems soon at normal voltages!
The best day was when a student used the speaker on one of the data lines and wrote a program to play the tune 'Daisy Daisy' (our version of HAL from 2001....), it coincided with the college Principal showing the Mayor what we were doing with his old computer! The Principal went 'ballistic' but the Mayor was delighted and saw it as creative and the most interesting thing he had ever seen done on it!

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March 31, 2014 17:59

That's interesting but doesn't solve my problem. Look at the home page of my website www.honeypi.org.uk which has nothing at all to do with the Raspberry Pi as it happens. In the first paragraph I mention the possibility of emulating a Honeywell 200 mainframe from 50 years ago, long before the machines that you mention were around, on a PC, but the problem is emulating the control panel visually. The lights on the panel were connected to the main memory address and data buses, so they flickered in time with every memory cycle. It's incredibly easy to emulate the internal processes of this antique computer, but I suspect that even a modern PC with directfb software would have a hard time displaying a realistic dynamic image of the control panel on its screen while running the emulator at the speed of the original computer. Of course I'd love it if someone could prove me wrong. If anyone wants to try I can provide the graphics for the control panel as used on my website to create the pictures. Personally I'd rather try to build the real computer than attempt that though.

Rob

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November 1, 2013 08:59

Great job, it is nice to see that hercules can run on anything, including the Raspberry Pi! Next step parallel sysplex ;-)

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August 12, 2013 10:29

Wow... a walk down memory lane. Interesting to think about that old stuff, but like you said, the comparisons are not really equivalent. Great stuff though.

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