DooM

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DooM

Postby JoJo_Reloaded » 2019-9-11 @ 16:14

Here is my latest build: DooM

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This is a try to build the beefiest 386 ever, along having other perks, such as many sound systems or doing live overclock to the CPU.

That's it, in this computer you can change the CPU speed in real time with the push of a button:

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At boot the system starts at its stock speed, 40mhz, but we can change it on the fly to 50, 55 and 60mhz. Apart from that, using the turbo switch we can select also 20, 25, 28 and 30mhz.

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DooM power is flowing through its veins...

Without further ado, here is the build running:

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https://www.youtube.com/watch?v=4uja0zSPkt8

Those are its specs:

- CPU 80386 DX (20 - 60 mhz)
- 8 mb de ram 60ns
- 128 kb cache 12ns
- Storage via a CF (using XT-ide bios)
- 3 1/2 1.44mb floppy
- SVGA [url="https://en.wikipedia.org/wiki/Tseng_Labs_ET4000"]Tseng Labs ET4000[/url] 1mb.
- Sound blaster 2.0 with CMS chips
- General Midi and Roland MT-32 support via [url="https://www.serdashop.com/S2P"]S2P[/url]
- TI SN76496 support via TNDLPT (prototype unit)

https://www.youtube.com/watch?v=W4XfvI7WkhQ

The system is compatible with these sound standards:

- pc speaker
- tandy / pcjr
- game blaster
- adlib
- sound blaster
- Roland MT-32
- General Midi

https://www.youtube.com/watch?v=rVu2r-gTifw

The origins of this build come from my overclock experiments. Yes, that's one of my hobbies, trying to overclock old PCs.

This of course needs many xtal or osc changes, but many times I can't find the correct one. I need a 37.5mhz one and only can find a 35mhz or a 40mhz...

I thought of building my own programabble oscillator and found this clock generator:

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The Adafruit Si5351A clock generator. This and an Arduino can generate square waves from 8khz to 160mhz with a compatible logic for 3v or 5v, perfect for my TTL system.

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Here is my custom oscillator adapted to a dip 14 socket.

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It's alive!

With that I tried several motherboards and found one, an AMD 386-40 one that surprised me...

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60mhz! Incredible!

I never thought of a 386 running at 60mhz, even it is not entirely stable. We can blame the cache memory for it, even upgaded from 20ns chips to 12ns, the cache tag chip is the same, and can't find a replacement that keeps the system stable at 60mhz. Maybe one day :)

In any case, at 55mhz the system is perfectly stable and we are talking a huge overclock here, +37.5%. The CPU overheats, but this is no problem...

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My initial tests were with that big-ass cooler, but after 30 minutes or so the system went unstable. We needed more juice, so, here enters the peltier:

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A 60w peltier keeps the CPU at stable temperatures, so that's it.

I used thermal glue to attach the cpu to the peltier, and more to join the peltier with the cooler, but the result was not as robust as I needed, because the cooler I'm using, one designed for Athlons XP, is somewhat heavy.

As these motherboards doesn't have any means to attach coolers I needed to attach it to the case, using a steel rod from side to side:

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For controlling the logic, the clock generation circuit, the select buttons, the system start button, and the skull eyes there is an Arduino UNO doing all the work...


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And for decoration I attached a lcd screen playing 'doom videos' with a raspberry pi...

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... and a Doom sticker:

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And that's all, I hope you like it!

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DooM is watching you...
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Re: DooM

Postby pshipkov » 2019-9-11 @ 20:15

Well, let me be the first to say:
Badassery !

Tell us more about the Peltier setup you got there.
Also, where is the upper limit where the system is long term stable, and how do you determine that ?

Thanks for sharing.
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Re: DooM

Postby mothergoose729 » 2019-9-11 @ 20:29

Truly the ultimate 386. I love it. Thanks for sharing.
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Re: DooM

Postby derSammler » 2019-9-11 @ 20:49

Very nice build. However, using a Peltier this way is very daring. First, it's very important to exactly calculate the heat that is to be dissipated from the CPU in order to choose the right Peltier element. Choosing one with too much power is bad, and 60 watt is way too much for a 386. The Peltier element should not have more than ten times the power of the CPU's TDP, otherwise it will cool down more than 5°C below room temperature and that causes water condensation (based on usual humidity), and also there's more heat you need to get out of the way. Because of this, it's not a good idea to use a Peltier element for cooling without having it controlled by a microcontroller. You need to monitor room temperature, CPU temperature, and heatsink temperature and control the Peltier element and the fan accordingly. I built a Peltier element cooling for a 5x86 some time ago and started that simple as well. You'll soon run into trouble by leaving it this way.

Also note that unlike what most people think, a Peltier element is not a cooling element. It's a heat pump actually. That is, if the fan/heatsink can not dissipate the combined heat from the CPU and the Peltier element, the "cold" side of it turns into a heater, destroying the CPU in no time. That's why temperature monitoring is crucial. And make sure the fan won't ever fail.
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Re: DooM

Postby pshipkov » 2019-9-12 @ 06:33

@derSamler
A much better formulation than my very fuzzy initial thought. :-D
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Re: DooM

Postby BinaryDemon » 2019-9-12 @ 06:39

So how fast do DooM on a 386-60mhz run?
Check out DOSBox Distro:

https://sites.google.com/site/dosboxdistro/ [*]

a lightweight Linux distro (tinycore) which boots off a usb flash drive and goes straight to DOSBox.

Make your dos retrogaming experience portable!
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Re: DooM

Postby JoJo_Reloaded » 2019-9-12 @ 08:07

Thank you all!

derSammler wrote:Very nice build. However, using a Peltier this way is very daring. First, it's very important to exactly calculate the heat that is to be dissipated from the CPU in order to choose the right Peltier element. Choosing one with too much power is bad, and 60 watt is way too much for a 386. The Peltier element should not have more than ten times the power of the CPU's TDP, otherwise it will cool down more than 5°C below room temperature and that causes water condensation (based on usual humidity), and also there's more heat you need to get out of the way. Because of this, it's not a good idea to use a Peltier element for cooling without having it controlled by a microcontroller. You need to monitor room temperature, CPU temperature, and heatsink temperature and control the Peltier element and the fan accordingly. I built a Peltier element cooling for a 5x86 some time ago and started that simple as well. You'll soon run into trouble by leaving it this way.

Also note that unlike what most people think, a Peltier element is not a cooling element. It's a heat pump actually. That is, if the fan/heatsink can not dissipate the combined heat from the CPU and the Peltier element, the "cold" side of it turns into a heater, destroying the CPU in no time. That's why temperature monitoring is crucial. And make sure the fan won't ever fail.


Yes, I am aware of this, and because of that the CPU is insulated with vaseline in all sides that condensation could happen. The system has been running more than a year like this*, have tested it for more than 4 hours straight at 55mhz and without any problems. I chose that cooler because it keeps the temperature just stable, and with the 12x12 fan on the case to extract the heat the system can run like that indefinitely.

Here you can see the 386 with the vaseline insulation, underneath, on the sides, and near the pins, that was a heck of a job with a thin brush.

http://vieju.net/pub/Imagenes/Doom/IMG_20180612_152608.jpg

after that I cleaned the top with alcohol, to make the best conductive surface with the thermal glue:

http://vieju.net/pub/Imagenes/Doom/IMG_20180612_152742.jpg

* I finished the system on July of 2018, but didn't had the time to collect all the pictures, document it, etc... I have been using it since then with no problems ;)
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Re: DooM

Postby Tertz » 2019-9-13 @ 20:43

paint the case to colors of Doom walls

> The CPU overheats, but this is no problem...

except it may degrade, near capacitors to reduce life time, etc
in case to use PC significant time, but not to keep it on a shelf
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Re: DooM

Postby FuzzyLogic » 2019-9-14 @ 12:27

I am in awe. Image.

That is the fastest I've seen Doom on a 386. Great job!

Also, that clock generator is nifty! I'd love to see you or someone create a small drop-in replacement with a few programmable settings and a header to connect a front panel button. I'd buy that.
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Re: DooM

Postby amadeus777999 » 2019-9-15 @ 12:58

Excellent work - props!
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Re: DooM

Postby oeuvre » 2019-9-19 @ 13:09

This is the craziest 386 build... awesome work! Congrats... absolutely insane.
Dell Precision T1650 Intel Xeon E3-1240v2, 16GB, NVIDIA Quadro 4000 2GB, SSD + HD, XP/7
Main Desktop Intel 6700, 32GB, AMD RX580 8GB, NVMe SSD + HD, 10
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Re: DooM

Postby ufoman2k » 2019-9-19 @ 16:03

You are the 386 master, my friend! :-D :-D :-D
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Re: DooM

Postby MaverickUK » 2019-9-20 @ 10:41

That's damn impressive. It never would have crossed my mind to create a modded case like that for a retro PC :)
http://www.strifestreams.com // Regular nuggets of retro gaming
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Re: DooM

Postby appiah4 » 2019-9-20 @ 12:46

But.. Can it run CrysisDooM?
A500:Rev6|+512K|ACA500+|C1084S
i386:Am386SX25|4M|GD5402|ES688|MuntPi3
i486:U5S33|8M|GD5428|YMF719|DB-S2
i586:P133|32M|T64+/MX2|V1|CT3980/32M
i686:K6-2/400|128M|V2/SLI|CT4520/32M
S370:P3-1200|384M|GF4-4200|MX300
S754:A3700+|2G|X1950PRO|SB0350
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Re: DooM

Postby ynari » 2019-10-11 @ 14:21

That's a stunning build. I mean, you're still completely nuts for doing it, but it's an impressive build nonetheless.
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Re: DooM

Postby root42 » 2019-10-11 @ 14:33

On a slightly related note: it has been 25 years soon the release of Doom II:
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80386DX@25 MHz, 8 MiB RAM, Tseng ET4000 1 MiB, Jazz16, PC MIDI Card + SC55MkII + MT32, XT CF Lite, OSSC 1.6
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