How would you overclock a Cyrix 5x86-120 to 133 Mhz that has a 3x multiplier? I can see using 50 Mhz FSB and a Host-PCI clock division of 2:3 for 150 Mhz.
there is very simple way. You have to discover hidden 66MHz fsb setting and set multiplier to 2x. Rg100 found Biostar hidden settings. You can read about this in second post here:
UMC chipset PCI 486 mobo. AMD P90 CPU options?
I'm sure that M919 also supports unofficial FSB settings.
I noticed that your Speedsys result for your overclocked Cyrix 5x86 to 150 Mhz showed worse performance than my stock Cyrix 5x86 […]
I noticed that your Speedsys result for your overclocked Cyrix 5x86 to 150 Mhz showed worse performance than my stock Cyrix 5x86-120 Mhz chip. What cache timings were you using? What about memory wait cycles? I use 2-1-2 on Biostar and 2-1-1-1 on M919, RAM wait states of 0. This configuration is long-term stable in WinNT 4.0 with all available 6x86 nextgen enhancements on (minus BTB). I am also using FPM 60ns (two sticks of 64 MB each).
For speedsys 5x86-120, I got:
L1: 173 MB/s, L2: 68 MB/s, RAM: 48 MB/s
For speedsys 5x86-150, you reported:
L1: 145 MB/s, L2: 63 MB/s, RAM: 44 MB/s
As I remember I used to use 1:1/2 divider, slowest cache timings and dram waitstates set to 1. I haven't remembered other settings (also I didn't use cx enhancements in this test).
Currently my 486 is disassembled because of damaged HDD drive (appeared bad sectors). I'm going to buy CF card for testing purpose - I don't want to annihilate another vintage hard drive.
In the other post, you mentioned that you needed to up your CPU voltage to 5.0 V. As opposed to 3.45 V? How did you come to this determination? Did you try 4 V? Did you try booting into Windows and if so how was stability?
I always start OC experiments by setting bios settings to slowest and voltage to highest. I have efficient copper cooling system, so I don't worry about CPU temperature.
When system behaves stable I start to tune up bios settings (always change only one option at one try). Then I check again how system behaves - if everything is ok, I try to reduce voltage and retest system. I repeat this until system works stable.
I made cx@150MHz test with voltage set to 5V. It didn't want to boot up with lower voltage.
As for stability this system couldn't boot to Windows because HDD was too damaged. Only speedsys, cpuchk and 3dbench were readable from HDD. Those two benchmarks worked correctly (but I know they are not good stress tests) I will retest this system in the future.
I briefly attempted this at 5V and 50 Mhz FSB but didn't get past memory check on my M919 w/128MB EDO RAM. It went to about 109,000 KB and froze.
How do you cool your CPU? You should use solid cooler and reasonable amount of thermal grease when voltage is set to 5V.
I think system froze because your CPU became too hot.
Also for overclocking experiments I recommend to use only one memory module (I used to use one 60ns FPM module).