"Speed pin" refers to the GPIO pin on the keyboard controller which controls the keyboard activated turbo switching (ctrl+alt+plus/minus)

It works like a dream with the keyboard (ctrl+alt+plus/minus). I knew part of that section was about the keyboard, but the bottom section called "Turbo Switch Input" made me think the physical switch connected to the motherboard header would work. Now I can play with some more with the configurations and benchmark them. Thank you very much for your help.

sdw wrote on 2025-05-04, 15:55:

It works like a dream with the keyboard (ctrl+alt+plus/minus). I knew part of that section was about the keyboard, but the bottom section called "Turbo Switch Input" made me think the physical switch connected to the motherboard header would work. Now I can play with some more with the configurations and benchmark them. Thank you very much for your help.

Hey! 😀
Did you by any chance got around to testing what does the "ctrl+alt+plus/minus", actually changes on this particular motherboard??
Does it disable anything or lowers any frequency?

I was kinda mulling over the idea of replacing the Turbo Button with a more complex button (with more contacts), and connect it to the FSB jumpers (with the shortest possible wires) in order to switch the BUS & Ram speed between 100 & 66 Mhz.
Only 2 jumpers need to be switched (with the PC turned off, of course.)

Yes it works with DOS. I never benchmarked it after making that bios change. If you are are still using the AMD K6-2+ there are lots of software you can use to change the clock frequency. Phil's computer lab has them on his site and there lots of videos on youtube.

https://www.philscomputerlab.com/k6-2-2-3-resources.html

Have fun,
SDW

Thanks for the link!
Yes, i'm using a K6/2+... But all the utilities presented by Phil, and that I know of; can't alter the FSB speed. Or disable the L3 Cache (which you have to do through the bios)

So unfortunately, unless you're willing to always mess with jumpers; a compromise has to be made when permanently setting the FSB:
100 Mhz -- and reaching the max potential of the system /or/ 66 Mhz -- and being able to obtain even lower speeds for dos games.

That's why I was hoping that the TURBO feature might do something that the software utilities can't.

It turns off L1 cache. I used modbin to enable "ON/OFF cache for speed change" setting under "Speed Pin Option" to get the ctrl+alt+plus/minus work. I tried enabling "Turbo Switch Input" and "Program Chipset for speed change" with the physical turbo switch on and off, but it did not make a difference. I really didnt know what I was doing. You might get the other settings to work.

I used the same setup as the bios version benchmark thread.
Problem with UDMA, need BIOS fix for Taken TX3 (LGS Prime 3C)

I valued the test results by going into the bios at boot up and turning off the "CPU Internal Cache".

Here is a screenshot from modbin of the settings.

Here is a speedsys screenshot of the same setup I used before with the system run full speed.

Here is a speedsys screenshot after pressing ctrl+alt+minus to slow it down (aka turn turbo off)

DOOM MAX - 15.72 FPS
Quake 360x480 - 2.9FPS
3DBench - 35.3

The 3DBench value puts the machine, per Phil's 136 in 1 CPU Benchmark sheet, the same as a 486 at approximately 50mhz.

I pulled out my K6-2+ 550mhz and clocked it at 6x for a speed of 600mhz. I turned the turbo off via keyboard and got almost identical numbers as above. It turned off L1 and L2 CPU cache off.
3DBench - 36.3

I then used K6INIT to turn off turn off L1, L2, Prefetch, and set the clock 2x, since it is software it sees it as 2 and not 6, for 200mhz.

3DBench - 29.3
Equivalent of a 486 at 33mhz

Have fun,
SDW

Screenshot of speedsys at this reduced speed.

I am not sure how slow you are trying to go, but this is pretty slow.

Have fun,
SDW