PC-XT core (from 8088 to 286 CPU)

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Mills
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PC-XT core (from 8088 to 286 CPU)

Post by Mills »

First of all, I want to thank the people who made MiSTer project possible, I know it is a lot of work to program the cores :D.

I asked this in newbie quwestions, but it is better to ask here I think.

The ao486 core is working great with sound and everything... But how difficult would be to add more cpu's to the core? (8088 4.77MHz / 8086 8MHz / 286 8-16MHz). And also add the CGA card (CGA is included in VGA, but it has some issues).

There is also the Next186, but it has not been ported to MiSTer, and it has only a 8186 cpu.

If someone is interested, I could help testing games / demos etc... once I get the de10-nano (I have a lot of time :) ).
But I won't be able to help with programming the core :().

Thanks again.
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Re: PC-XT core (from 8088 to 286 CPU)

Post by bhamadicharef »

From the opencores page at https://opencores.org/projects/next186_soc_pc
The author mentioned implementations on two FPGAs close in DE-XX family

- DE2-115 (Altera EP4CE115F29C7) - runs at 105Mhz bus, 52.5Mhz CPU, 135Mhz(540MB/s)
SDRAM (64MB), 97Mhz DSP, 9248LE (8% from 114480), VGA24bit

- DE0-Nano (Altera EP4CE22F17C6N) - runs at 100Mhz bus, 50Mhz CPU, 147Mhz(294MB/s)
SDRAM (32MB), 100Mhz DSP, 13691LUT4 (61% from 22320), VGA18bit

So we can hope someone will not have much trouble getting it ported to the MiSTer.
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Re: PC-XT core (from 8088 to 286 CPU)

Post by Newsdee »

Can't you use a slowdown TSR to make ao486 run at a lower speed?
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Re: PC-XT core (from 8088 to 286 CPU)

Post by SuperBabyHix »

Newsdee wrote:Can't you use a slowdown TSR to make ao486 run at a lower speed?
Though I haven't tried on the Mister, I can say that on real hardware it is near impossible to slow a machine down to exactly XT speed. That being said I doubt the Next186 core can either. That original 8088 4.77Mhz speed is hard to achieve without that specific hardware.

The other thing I can say about slowing down actual PC MS-DOS hardware is that the most acceptable best practice for slowing machines down is disabling caches. Many slow down utilities use things such as wait states and can introduce stuttering and hitching in games. Disabling caches usually causes a large drop in speed, but it is consistent and smooth. That being said using this method does not allow for fine tuning and the older the processor the less dramatic the performance drop.
Mills
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Re: PC-XT core (from 8088 to 286 CPU)

Post by Mills »

SuperBabyHix wrote: ...the most acceptable best practice for slowing machines down is disabling caches. Many slow down utilities use things such as wait states and can introduce stuttering and hitching in games. Disabling caches usually causes a large drop in speed, but it is consistent and smooth. That being said using this method does not allow for fine tuning and the older the processor the less dramatic the performance drop.
I have a pentium 200, and disabling caches turns it into a 386 25 Mhz, according to the tests I run in it.

For the 286 8086/88 we'll have to use something like the Next186.

Last years I started programming things for that slow PC's, after watching the 8088MPH demo :). When you start to play with the hardware registers, (in ways most games or programs don't use), emulators are very inaccurate (the closest to a real machine is PCem).

Finding a real machine is now nearly impossible, so having this on MiSTer would be awesome.
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Re: PC-XT core (from 8088 to 286 CPU)

Post by bhamadicharef »

Anyone tried to synthesise the opencores rtf8088 to check what is the max frequency at which it can run ?
https://opencores.org/projects/rtf8088
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Mills
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Re: PC-XT core (from 8088 to 286 CPU)

Post by Mills »

Here we have another 8186 PC with VGA and everything: https://github.com/jamieiles/80x86

It says it has a cyclone V version, and works on DE0-Nano at a maximun of 60 MHz. So maybe it can work at any speed and simulate slow 8086-286 PC's.
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Re: PC-XT core (from 8088 to 286 CPU)

Post by Sorgelig »

I will look into that core.
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Re: PC-XT core (from 8088 to 286 CPU)

Post by Glaurung »

Mills wrote:Here we have another 8186 PC with VGA and everything: https://github.com/jamieiles/80x86

It says it has a cyclone V version, and works on DE0-Nano at a maximun of 60 MHz. So maybe it can work at any speed and simulate slow 8086-286 PC's.

Whoa,this is promising....with working VGA...hope rhat can be ported to mister soon.

The core is supplied as synthesizable SystemVerilog, along with a C++ reference model, extensive tests, a reference BIOS implementation and reference FPGA designs.
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Re: PC-XT core (from 8088 to 286 CPU)

Post by nightshadowpt »

This is very interesting... I was asking a similar question in the AO486 core thread.

Having the ability to slow down the AO486 core in the options would be amazing, but having an alternative core to play the older games is good as well.

Hope devs have the time/interest.

Cheers.
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Re: PC-XT core (from 8088 to 286 CPU)

Post by BitsNStuff »

It doesn't show a much really but he does have a short video on YouTube from 2017.

https://www.youtube.com/watch?v=YHjs2mpkN88
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Re: PC-XT core (from 8088 to 286 CPU)

Post by leejsmith »

I really want a Tandy 1000 core, they have some great games and for me in the UK it's very hard to find a real one.
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Re: PC-XT core (from 8088 to 286 CPU)

Post by djmartins »

leejsmith wrote:I really want a Tandy 1000 core, they have some great games and for me in the UK it's very hard to find a real one.
Isn't that just a PC compatible machine?
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Re: PC-XT core (from 8088 to 286 CPU)

Post by BBond007 »

djmartins wrote:
leejsmith wrote:I really want a Tandy 1000 core, they have some great games and for me in the UK it's very hard to find a real one.
Isn't that just a PC compatible machine?
It is more of an IBM PC Jr compatible. PC Jr was a failure early on, so Tandy just called the machine "DOS Compatible"

It is CGA compatible but also has 16 color graphics modes that are not compatible with EGA. Obviously 16 color graphics look a lot better than the grungy 4 color CGA. It also has 3 voice sound like the PC Jr. Sierra games, in particular, took full advantage of the enhanced audio and video capabilities.

I would recommend this 8-bit Guy video for information on the Tandy 1000 line --> https://www.youtube.com/watch?v=mYHtojsaRkY
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Re: PC-XT core (from 8088 to 286 CPU)

Post by djmartins »

BBond007 wrote:It is more of an IBM PC Jr compatible. PC Jr was a failure early on, so Tandy just called the machine "DOS Compatible"

I remember the PC Jr.
Not a machine many care about to be honest.
A DOS core that can play a most of the DOS games would be far nicer.
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