PCXT Core 10Mhz CPU Speed Possible?

[breiztiger]

For me next step should be 8086 and 8087

[Malor]

The 80286 executes the same instructions much faster than an 8088 and you would probably need an 8088 running at ~90mhz to equal an 80286 running at 12 mhz. This core might eventually run that fast though. I do believe that eventually between the two cores we'll be able to handle most fringe cases as ao486 continues to slowly improve over time.

Are you sure? I thought the major difference was in MUL, IMUL, DIV, and IDIV instructions, but in overall instructions/clock they are pretty similar?

I'm absolutely positive. The 8088 was already hampered by the 8-bit bus and operated at about half the speed of a 8086 for most tasks. Then you had two more generations of speed optimizations with the 80286. It operated so much faster at the same Mhz.

I owned a 12MHz '286, and I certainly don't remember it that way. It was faster than the XT-style PC Bridgeboard I'd owned previously, but it was like four or five times faster, not fifty.

[dmckean]

That's why we have benchmarks, you can't just go by how it feels. The jump in performance between the XT and AT was as big as the jump between the 286 and 486.

[Mills]

For the same reason, I wonder if a 286 core makes sense at all, given that ao486 covers basically all of the needs that a 286 is capable of. Beyond the preservation of specific popular computers like the 5160 or the PS/2, I don't see a need for such a core.

I think it would be awesome but just for preservation of the cpu, because it has instructions an 8088/86 doesn't, and also it is very different to a 386, or 486. But there is no need for cycle accuracy, because there are different 286 cpus, (intel, amd ...).

If you have to compare speeds, I now own a 286 6/12MHz, at 6 it is more or less 2, or 2.5 times as fast as an 8088 7, but not a huge difference. At 12 it is very noticeable, but it is not the fastest thing on the universe, it just makes many vga games, or windows 3.1 playable/usable

[thorr]

But there is no need for cycle accuracy, because there are different 286 cpus, (intel, amd ...)

Very respectfully, I could not disagree more. Intel would be the one to replicate in my opinion.

[dmckean]

This discussion probably belongs in this thread:

viewtopic.php?t=5043

Just keep in mind that there's only a handful of people working on this project that are capable of recreating an i286 or i386, assuming there exists the documentation to do so. This PCXT core came together fast because it was already 80% written and mostly needed assembled and debugged. A 286 core will be starting from zero and is much more complex, about the same complexity as the AtariST and Minimig cores.

[suww37]

I've updated the prerelease branch with @kitune-san's latest changes, and updated the OSD to indicate that the maximum speed corresponds to a PC/AT 286 at 3.5MHz (I attach the binary):


CPU speeds OSD.png


On the other hand, I have taken the opportunity to update the joystick counter values taking into account the new CPU speed models, so that they are synchronised with it as long as the corresponding option is checked in the OSD, in this way, the paratrooper game cannon will always appear centred when the joystick has no movement:


Paratrooper.png

Your pcxt-prerelease results in a boot error in IBM pcxt BIOS. Tandy BIOS is normal.

[spark2k06]

Your pcxt-prerelease results in a boot error in IBM pcxt BIOS. Tandy BIOS is normal.

Please be more specific.

What error exactly? screenshot... Which BIOS exactly? The IBM5160, another one of PCXT? On what CPU speed setting.... and what version of prerelease? because I've already sent several... until sorgelig updates Main I won't be able to send all the pending updates we have and it is being a little chaotic at the moment.

[suww37]

Your pcxt-prerelease results in a boot error in IBM pcxt BIOS. Tandy BIOS is normal.

Please be more specific.

What error exactly? screenshot... Which BIOS exactly? The IBM5160, another one of PCXT? On what CPU speed setting.... and what version of prerelease? because I've already sent several... until sorgelig updates Main I won't be able to send all the pending updates we have and it is being a little chaotic at the moment.

[suww37]

Your pcxt-prerelease results in a boot error in IBM pcxt BIOS. Tandy BIOS is normal.

Please be more specific.

What error exactly? screenshot... Which BIOS exactly? The IBM5160, another one of PCXT? On what CPU speed setting.... and what version of prerelease? because I've already sent several... until sorgelig updates Main I won't be able to send all the pending updates we have and it is being a little chaotic at the moment.

I used a speed patched (AT 3Mhz) pcxt-prerelease.

[spark2k06]

Your pcxt-prerelease results in a boot error in IBM pcxt BIOS. Tandy BIOS is normal.

Please be more specific.

What error exactly? screenshot... Which BIOS exactly? The IBM5160, another one of PCXT? On what CPU speed setting.... and what version of prerelease? because I've already sent several... until sorgelig updates Main I won't be able to send all the pending updates we have and it is being a little chaotic at the moment.

I used a speed patched (AT 3Mhz) pcxt-prerelease.

Update the ROMs with the ones from the prerelease branch... a new XTIDE is required to be embedded in these.

https://github.com/MiSTer-devel/PCXT_Mi ... se/SW/ROMs

[suww37]

Please be more specific.

What error exactly? screenshot... Which BIOS exactly? The IBM5160, another one of PCXT? On what CPU speed setting.... and what version of prerelease? because I've already sent several... until sorgelig updates Main I won't be able to send all the pending updates we have and it is being a little chaotic at the moment.

I used a speed patched (AT 3Mhz) pcxt-prerelease.

Update the ROMs with the ones from the prerelease branch... a new XTIDE is required to be embedded in these.

https://github.com/MiSTer-devel/PCXT_Mi ... se/SW/ROMs

Thank you . I solved it