What I would like to do is to change with, say a 486DX/4-133, between, say, 1x, 2x, 3x and 4x.
So the processor works with 33MHz (respective bus frequency), 66, 100 and 133, respective.
Is this possible?
if it is possible, does it work the same way on all 486 or only on particular types/brands?
I highly doubt it. They most likely have different dies for each version of the 486.
"And remember, this fix is only temporary, unless it works." -Red Green
For the Intel DX4, you can switch between 2x, 2.5x and 3x by using the CLKMUL pin (assuming the motherboard has jumpers that support it or you manually connect the pins):
Similarly, the AMD 5x86 can do 3x or 4x. Not sure about Cyrix chips though.
For earlier chips (DX2) the internal multiplier is fixed at 2x.
For 486 DX4 and AMD 5x86 chips it looks like you may be able to change between 2x/3x and 3x/4x respectively. See here for some info:
http://web.inter.nl.net/hcc/J.Steunebrink/amd5x86.htm
For a Cyrix 5x86, you can use setmul to change between 1x and the multiplier set via the motherboard jumpers.
If you have a 4x capable Cyrix 5x86, you can switch between 1x, 2x, and 4x as is documented here: (not sure where the original post is.
ftp://retronn.de/driver/CPU/VOGONS%20%E2%80%A … ious%20CPUs.htm
I think it's more or less just an on/off switch for DX4 and all clones.
I must be some kind of standard: the anonymous gangbanger of the 21st century.
Thank you all for these helpful replies!
I will have to let all that information settle to decide which approach I try first.
The idea is to implement some kind of "gear" for adjusting the speed of a retro game rig for games from PC 4.77 to end-486.
So it looks possible to implement a 4-speed-gear on a steampunk rig 😀
Btw, if I do a 5-speed-gear, it will do it only if possible without overclocking, as everybody knows that switching from gear 4 to R (= Race) usually doesn't turn out well 😉
Will report back when I did some experiments 😀
