MiSTer PCXT

[suww37]

At that time, the xt pc cpu speed was mostly 10 MHz and could be changed at a low speed via the switch.

Yes, I agree with you too; for games of 1989 and beyond we'd need at least 10Mhz (and it is planned). I was lucky enough that around '93 I already had a 486sx25 with VGA and a crappy SB clone... but I remember many of my relatives still having machines with Turbo buttons around that time.

As spark2k06 mentioned, the ao486 core can be used for that... you just need to slow it down by setting the CPU clock to 15Mhz and disable the L2 CPU cache. I'm not sure what kind of system you'd end up with but it would be fairly slow - slower than a 386SX20. Of course it won't support Tandy graphics, but most CGA games (and EGA/VGA) would work fine with it.

I know how to slow down by turning off ao486's L2 cu chache. But even with that method, the speed of XT and AT games from the late 80s to the early 90s is awkward. Crucially, ao486 does not support monochrome (b/w, green,amber) effects and does not support cga, hercules, or tandy graphics cards.

[dmckean]

I agree with suww37 here. The ao486 core has a lot of issues running older games from the XT/AT era and if this core could eventually run at the speed of 8Mhz AT it could prove very useful.

One other tip though that I learned from playing around with cores on MiSTer is that the best versions of games from the 286/AT era are often on Atari ST or Amiga.

[thorr]

After everything is completed with this core with Tandy which will be totally awesome, I hope we can get a 286 core. There are some games that work great on 286/12 and 286/16, and anything else needs to be slowed down because it runs too fast. What I really would like is a selection of any CPU, graphics card, etc., like in PCEM, with cycle accuracy.

Also, I am hoping that Tandy digital sound support will be supported: https://youtu.be/kbp094HDZ20?t=210

[kitune-san]

I am trying 7MHz on the core right now.
It will take time.
Wait.

[Newsdee]

Does anybody know any games that exclusively require Hercules graphics?

I've started looking into MDA and CGA 16 color games... they are a nice little curiosity that already work on the core.

[suww37]

Does anybody know any games that exclusively require Hercules graphics?

I've started looking into MDA and CGA 16 color games... they are a nice little curiosity that already work on the core.

I know that few games only support hercules. Hercules graphic card is needed for high-resolution (720x350, 720x348) graphics to represent their languages in countries that don’t use English. However, the most games didn't support hercules, so people using hercules graphic card needed a program called simcga.com emulating cga graphics cards. However, for those who have a sense of retro pc, they prefer emulated graphics with simcga.com on the hercules graphics card.

[suww37]

After everything is completed with this core with Tandy which will be totally awesome, I hope we can get a 286 core. There are some games that work great on 286/12 and 286/16, and anything else needs to be slowed down because it runs too fast. What I really would like is a selection of any CPU, graphics card, etc., like in PCEM, with cycle accuracy.

Also, I am hoping that Tandy digital sound support will be supported: https://youtu.be/kbp094HDZ20?t=210

I also desperately want someone to develop the PCAT (286) core when the PCXT core is completed. Many of the 286 games are not suitable for running on ao486.

[thorr]

Does anybody know any games that exclusively require Hercules graphics?

I've started looking into MDA and CGA 16 color games... they are a nice little curiosity that already work on the core.

The game I remember playing in Hercules was Sokoban. It looked great with the high resolution. I don't recall if it worked in other modes.

Edit: I am pretty sure this was it, and obviously it supports CGA too: https://www.youtube.com/watch?v=_iZLe05aJuU

[Bas]

This may be true but when using the PCXT with the image mounted on the serial port the size of the image calculated from the geometry has better to match the size of the file. If not the image will not be mounted.

The geometry of the "disk" must match what the emulated controller expects. There are multiple ways to translate a given size to CHS. If you get that wrong, things break like they used to in the 80's

[spark2k06]

I am trying 7MHz on the core right now.
It will take time.
Wait.

It would be great to have at our disposal the possibility of a turbo mode, or several up to the maximum that MCL86 can give, you probably already know this, but please note the comments made by @MicroCoreLabs on the subject:

...

As I mentioned before, to run the BIU at anything other than 4.77 Mhz will require some updating to make it sensitive to the bus clock. Currently it only looks at a single 4.77 Mhz clock edge and then paces the rest of the activity using 100 Mhz clocks. This is a simple update, but you will get much more impressive results in other ways.

First of all it is easy to disable the MCL86 clock accuracy with just one line of Verilog which can provide a performance improvement in the 20% range.

But the big speed improvements come when the four-cycle BIU state machine is bypassed when accessing RAM and ROM. The most recent time I did this was on the MCL86jr which uses an SRAM external to the FPGA running at 100Mhz. I dont think I was mirroring the BIOS ROMs and was able to achieve a 4X speed improvement which would be close to a 20 Mhz PCXT equivalent. If you mirrored the BIOS ROM it would be even faster.

...

[spark2k06]

DSS/Covox compatibility added to prebeta 1.4:

https://github.com/spark2k06/PCXT_MiSTe ... 5cacf07284

dss_covox.jpg (111.5 KiB) Viewed 3003 times

By default, it would be unplugged.

[kitune-san]

Current status report.
By changing biu and setting BIU_CLK_COUNTER_ZERO=1'b1, it is still at 4.77MHz but slightly faster.
The next step is to increase the clock to 7 MHz, but it looks like the memory module needs to be modified.

[kitune-san]

I am currently investigating only 8088BIOS.

[Newsdee]

I also desperately want someone to develop the PCAT (286) core when the PCXT core is completed. Many of the 286 games are not suitable for running on ao486.

What features/specs would you want to see in a AT/286 core? (assuming it would sit between the XT core and the full featured ao486)

[suww37]

"make_boot_with_tandy.py" does not work. I went to the "http://retrograde.inf.ua/files/T1K_0101.ZIP" link directly in a web browser, but this site did not open and I could not receive the file. There seems to be something wrong. Are you guys all right? I'm sorry, but I would appreciate it if you could send me boot.rom with tandy bios by message.

[dmckean]

I also desperately want someone to develop the PCAT (286) core when the PCXT core is completed. Many of the 286 games are not suitable for running on ao486.

What features/specs would you want to see in a AT/286 core? (assuming it would sit between the XT core and the full featured ao486)

If someone wants to create a separate topic for a future possible AT core we can go into more detail there but it's really off topic in this thread.

[akeley]

I've created a couple of blank HDD images using pgimeno's instructions.
Both images have default geometry, so they will work with the default serdrive command (#)

One is 20MB (as per the example), and I've tried to make a 31MB one as well.
Their filename is .vhd so that you can mount them in ao486 and format them with the OS of your choice (thanks Flynnsbit for the tip!)

I've tried to format the 20MB vhd both in ao and pcem but get "invalid drive specification" error.

I used to make vhds for ao in windows and they work ok, but I suppose in this case I need to define exact geometry parameters? Can it be done in Windows?

EDIT: scratch that, forgot I need to use fdisk before format. Have formatted it, but ao486 still doesn't see it. Ok, it sees it but my normal everyday vhd with DOS 6.22 and Dos Navigator doesn't.

EDIT2: ok, sys c: solved my problems, and it's all now working fine in ao486 - I can boot and play games from this hdd, but PCXT core does not recognise it. I have boot.rom & serdrive in the games directory, also tried different names and edited the script, but it's not being detected.

[suww37]

I also desperately want someone to develop the PCAT (286) core when the PCXT core is completed. Many of the 286 games are not suitable for running on ao486.

What features/specs would you want to see in a AT/286 core? (assuming it would sit between the XT core and the full featured ao486)

Games that used to run at normal speed on a 286(AT) PC (eg "Death track" ) are too fast on a 386 pc or 486 pc to play the game. In fact, the 10MHz XT pc is enough to enjoy games from the late 80s to early 90s, but the 286 (PC) has a fast loading speed and allows you to enjoy it comfortably.

[spark2k06]

I also desperately want someone to develop the PCAT (286) core when the PCXT core is completed. Many of the 286 games are not suitable for running on ao486.

What features/specs would you want to see in a AT/286 core? (assuming it would sit between the XT core and the full featured ao486)

Games that used to run at normal speed on a 286(AT) PC (eg "Death track" ) are too fast on a 386 pc or 486 pc to play the game. In fact, the 10MHz XT pc is enough to enjoy games from the late 80s to early 90s, but the 286 (PC) has a fast loading speed and allows you to enjoy it comfortably.

The load speed right now is limited by the use of the UART port, up to 115.2Kbps, and not by the fact that it is XT... so if that was the only drawback, it will be solved when we have IDE interface, the rest will probably be solved by a 10 or 12Mhz turbo mode, but probably even more will be possible, as @MicroCoreLabs commented.

[MicroCoreLabs]

The load speed right now is limited by the use of the UART port, up to 115.2Kbps,

What is limiting the speed to 115,200? If the UART and signal nets are all on-chip then can it be set to a higher speed?

[spark2k06]

The load speed right now is limited by the use of the UART port, up to 115.2Kbps,

What is limiting the speed to 115,200? If the UART and signal nets are all on-chip then can it be set to a higher speed?

I don't know why I had got it into my head that the maximum was 115.2Kbps, but that's not the case:

https://www.xtideuniversalbios.org/wiki/SerialDrives

Please, someone try to set it to a higher speed and tell us something, I'm not at home right now to test it.

[thisisamigaspeaking]

The ao486 core is great for running 386 or 486 early versions of the PC. But it’s not the right core for playing XT and AT games from the late 80s to the early 90s. I can adjust the speed by adjusting the L1 and L2 cache switches, but it's hard to find the right speed and it's awkward to barely set the diarrhea speed. And ao486 does not support cga, herclues, or tandy garphic and does not have a monochrome monitor effect (b/w, green, amber). And the opl2 sound is not perfect. I told sorgelig about this, but he's not interested. As you mentioned earlier, he doesn’t seem to be interested in XT, AT pc and thinks the Ao486 core is enough. I am very grateful for the PCXT core you have developed and are eagerly hoping that the turbo option and hercule graphic will come true.

I'm still waiting on my SDRAM to arrive and I haven't been able to try anything out, so I can't say from experience how true this is.

I would very much like to have a core that is fine tuned for CGA/Tandy/EGA/Hercules, AdLib and Tandy sound, 10 MHz XT / AT speed. To me that is the sweet spot (sweet range) for 80s PC games and it would be great to dial it in perfectly. Of course I had a 10MHz 8088 with EGA and (ultimately) AdLib so maybe I am biased... As I remember there were some games that only had 16 colors on Tandy, no EGA, and I believe some that had EGA and no Tandy. I'd love to cover all those bases with one core.

As I also remember there were some cool shareware games with 720x348x2 Hercules and 640x350x16 EGA. That's a secondary priority for me compared to the 320x200 modes but it kind of all goes together with that era.

If that isn't the direction this particular core is heading maybe there could be a "PCAT" or "PCclone" or "PC87" (for the approximate year EGA/Tandy peaked, the 1000 HX was released, and the year AdLib came out, although that's the same year VGA was released).

[spark2k06]

I have multiplied the speed of uart_clk by 4, now it is possible to change the script to work up to 460.8Kbps

Attached binary.

[dmckean]

The ao486 core is great for running 386 or 486 early versions of the PC. But it’s not the right core for playing XT and AT games from the late 80s to the early 90s. I can adjust the speed by adjusting the L1 and L2 cache switches, but it's hard to find the right speed and it's awkward to barely set the diarrhea speed. And ao486 does not support cga, herclues, or tandy garphic and does not have a monochrome monitor effect (b/w, green, amber). And the opl2 sound is not perfect. I told sorgelig about this, but he's not interested. As you mentioned earlier, he doesn’t seem to be interested in XT, AT pc and thinks the Ao486 core is enough. I am very grateful for the PCXT core you have developed and are eagerly hoping that the turbo option and hercule graphic will come true.

I'm still waiting on my SDRAM to arrive and I haven't been able to try anything out, so I can't say from experience how true this is.

I would very much like to have a core that is fine tuned for CGA/Tandy/EGA/Hercules, AdLib and Tandy sound, 10 MHz XT / AT speed. To me that is the sweet spot (sweet range) for 80s PC games and it would be great to dial it in perfectly. Of course I had a 10MHz 8088 with EGA and (ultimately) AdLib so maybe I am biased... As I remember there were some games that only had 16 colors on Tandy, no EGA, and I believe some that had EGA and no Tandy. I'd love to cover all those bases with one core.

As I also remember there were some cool shareware games with 720x348x2 Hercules and 640x350x16 EGA. That's a secondary priority for me compared to the 320x200 modes but it kind of all goes together with that era.

If that isn't the direction this particular core is heading maybe there could be a "PCAT" or "PCclone" or "PC87" (for the approximate year EGA/Tandy peaked, the 1000 HX was released, and the year AdLib came out, although that's the same year VGA was released).

EGA/VGA support is actually a possibility in the future since TubeTime lists EGA/VGA support as a future goal in the readme for Graphics Gremlin (which is what this core uses for video). I'm not sure that he's aware that this project exists however.

[thisisamigaspeaking]

The load speed right now is limited by the use of the UART port, up to 115.2Kbps,

What is limiting the speed to 115,200? If the UART and signal nets are all on-chip then can it be set to a higher speed?

Don't know anything about the details of this on MiSTer or in FPGA, but I believe that's the maximum speed of an 8250 and the oscillator was always the same. Would a different clock speed affect anything other than the UART itself?

[thorr]

I hope EGA, VGA and Hercules are all added at some point so we can select whatever we want and configure the software to use it. Also, if a Turbo function is added that goes slightly beyond the original XT hardware (ideally equivalent to 286/12&16 speeds), then it would probably meet the needs of most situations for the early PC days unless there are some specific 286 CPU instructions not available on XT's.

[thisisamigaspeaking]

I hope EGA, VGA and Hercules are all added at some point so we can select whatever we want and configure the software to use it. Also, if a Turbo function is added that goes slightly beyond the original XT hardware (ideally equivalent to 286/12&16 speeds), then it would probably meet the needs of most situations for the early PC days unless there are some specific 286 CPU instructions not available on XT's.

There are 286 instructions and games that used extended memory (XMS) are going to require them. EMS could work but I don't remember how many games used EMS, I don't think too many.

[thisisamigaspeaking]

The ao486 core is great for running 386 or 486 early versions of the PC. But it’s not the right core for playing XT and AT games from the late 80s to the early 90s. I can adjust the speed by adjusting the L1 and L2 cache switches, but it's hard to find the right speed and it's awkward to barely set the diarrhea speed. And ao486 does not support cga, herclues, or tandy garphic and does not have a monochrome monitor effect (b/w, green, amber). And the opl2 sound is not perfect. I told sorgelig about this, but he's not interested. As you mentioned earlier, he doesn’t seem to be interested in XT, AT pc and thinks the Ao486 core is enough. I am very grateful for the PCXT core you have developed and are eagerly hoping that the turbo option and hercule graphic will come true.

I'm still waiting on my SDRAM to arrive and I haven't been able to try anything out, so I can't say from experience how true this is.

I would very much like to have a core that is fine tuned for CGA/Tandy/EGA/Hercules, AdLib and Tandy sound, 10 MHz XT / AT speed. To me that is the sweet spot (sweet range) for 80s PC games and it would be great to dial it in perfectly. Of course I had a 10MHz 8088 with EGA and (ultimately) AdLib so maybe I am biased... As I remember there were some games that only had 16 colors on Tandy, no EGA, and I believe some that had EGA and no Tandy. I'd love to cover all those bases with one core.

As I also remember there were some cool shareware games with 720x348x2 Hercules and 640x350x16 EGA. That's a secondary priority for me compared to the 320x200 modes but it kind of all goes together with that era.

If that isn't the direction this particular core is heading maybe there could be a "PCAT" or "PCclone" or "PC87" (for the approximate year EGA/Tandy peaked, the 1000 HX was released, and the year AdLib came out, although that's the same year VGA was released).

EGA/VGA support is actually a possibility in the future since TubeTime lists EGA/VGA support as a future goal in the readme for Graphics Gremlin (which is what this core uses for video). I'm not sure that he's aware that this project exists however.

Checking out the notes it also mentions Tandy as yet to be implemented but it is already available?

Maybe the (S)VGA implementation could be copied from ao486? Is the difference between VGA and SVGA just the supported clocks? It should support all the EGA modes too right?

[dmckean]

Checking out the notes it also mentions Tandy as yet to be implemented but it is already available?

Maybe the (S)VGA implementation could be copied from ao486? Is the difference between VGA and SVGA just the supported clocks? It should support all the EGA modes too right?

It doesn't, you need to remember what the ao486 is. It's a translation of the Bochs AI-32 instruction set to verlilog done by automated tools and it's been heavily optimized with large amounts of cache and some pipelining to run at acceptable speeds. Most of its modules work ok now but are not all that accurate to real hardware.

This project has different goals and to be as cycle accurate as possible is one of them.

[spark2k06]

I hope EGA, VGA and Hercules are all added at some point so we can select whatever we want and configure the software to use it. Also, if a Turbo function is added that goes slightly beyond the original XT hardware (ideally equivalent to 286/12&16 speeds), then it would probably meet the needs of most situations for the early PC days unless there are some specific 286 CPU instructions not available on XT's.

There are 286 instructions and games that used extended memory (XMS) are going to require them. EMS could work but I don't remember how many games used EMS, I don't think too many.

For 286, XMS, etc... your core is Next186, but the adaptation work from the MiST stable port is not easy, this is your thread:

viewtopic.php?t=4533#p48943

I don't intend to focus this core in this direction... other improvements like a turbo mode however, if acceptable.