so it seems it's not just 3d realms, magic carpet has this too. and i noticed that in blood if i set the mouse sensitivity to 1, it works for a short while then dies again.

can the be because of some integer incompatibility in cyrix processors? maybe when it switches to protected mode *and* the mouse with some specific kind of arithmetic *and* some other condition is met then it dies? having it work then suddenly die looks like a silent buffer overflow or an IRQ conflict. and since we pretty much ruled out the latter one since it works everywhere else, i'm going to try to play with 5x86.exe a bit more.

if anyone has any idea, please reply. i'll post my findings if there are any for posterity.

- lowering ISA bus speeds

How much did you lower it?

Note that when it's a PS/2 mouse, you also have to make sure not to overclock the keyboard controller. There should be an option to set its speed as well in the BIOS.

derSammler wrote:

How much did you lower it?

PCLK/8, the lowest possible value in amiBIOS. since my clock is 100mhz by default, this should be.. 12mhz?

derSammler wrote:

Note that when it's a PS/2 mouse, you also have to make sure not to overclock the keyboard controller. There should be an option to set its speed as well in the BIOS.

nah, it's a microsoft (actually a rebranded mouse systems) serial mouse. keyboard clock has no effect on it..

EDIT: i didn't say it's a serial mouse in the OP even though thought i did

PCLK/8, the lowest possible value in amiBIOS. since my clock is 100mhz by default, this should be.. 12mhz?

That could be your problem, because with PCLK/8, you are running the ISA bus with only 4.1 MHz! You need to set it to PCLK/4, since the FSB of 33 MHz is the reference here, not the speed of the CPU (which is internal only and not relevant for any external clocks). This should work with an FSB of 40 MHz as well. If ISA runs to slow, it may miss data to transfer, if it's too fast (>10 MHz), most i/o chips will stop working correctly. You should always aim for something between 8 and 10 MHz.

derSammler wrote:

PCLK/8, the lowest possible value in amiBIOS. since my clock is 100mhz by default, this should be.. 12mhz?

That could be your problem, because with PCLK/8, you are running the ISA bus with only 4.1 MHz! You need to set it to PCLK/4, since the FSB of 33 MHz is the reference here, not the speed of the CPU (which is internal only and not relevant for any external clocks).

good idea, but i tried with all the dividers.. no luck there. : (

Then you could try using COM2 or a different multi i/o card.

derSammler wrote:

Then you could try using COM2 or a different multi i/o card.

well the only other machine i have from this era is a dead IBM aptiva that has all the I/O integrated on the motherboard, which is in fact where i got the cyrix processor in the first place. not to mention it's PS/2. anyway, i could order another ISA I/O card from ebay, but that's expensive and only a workaround - the mouse works flawlessly with the AMD 486DX4-100.

what is interesting is that i tried COM2 but the mouse doesn't respond there. even if i explicitly specify it with /S2 using ctmouse. maybe the other serial port is dead on the card or the extension cable is torn.. will have to look into that. thanks. : )

so i got another motherboard with PCI slots, an LS-486 rev. c1.. and everything worked fine right up to the point when i inserted the cyrix chip. jumpers were set correctly, and orientation double-checked. however, starting duke nukem again led to a freeze. i thought it's the cyrix acting up again and put the AMD 5x86 133 back. but since then no matter what i do 2d realms games and even emm386.exe loaded as a driver make the machine freeze.

i tried removing all unnecessary ISA cards, moving them to different slots, cleaning the CPU socket and die, using different CPUs, removing all but one FPM RAM stick, running memtest, nothing helps..

what is interesting is that descent sometimes runs sometimes says 'unexpected drop to real mode'. so that leads to me thinking that accessing UMB *and* running in 32-bit protected mode makes the machine hang. but what can be causing this?

Check your BIOS memory settings and enable Hidden Refresh.

appiah4 wrote:

Check your BIOS memory settings and enable Hidden Refresh.

there is no such option. tried enabling 'DRAM slow refresh' but it didn't change anything.

bamdad wrote:

appiah4 wrote:

Check your BIOS memory settings and enable Hidden Refresh.

there is no such option. tried enabling 'DRAM slow refresh' but it didn't change anything.

Not the same thing. Im 99% certain you need that. Unfortunately not all mainboards have the option 😒

funny thing is that this happened after the installation of the cyrix processor. and even a hard cmos reset didn't fix it..

this is so weid. i tried everything, removed every ISA card and the PCI video card, then put the old trusty ET4000 in, did a CMOS reset with the jumper, booted DOS with only command.com.. and still, hangs are there. i'm starting to suspect that there's some fault in that cyrix processor that simply killed some part of my motherboard (e.g. the one responsible for UMBs - sorry i'm not an x86 architecture expert) and that's why this is happening.

if anyone has any ideas, i'm all ears.

Maybe a stick of RAM is flakey?

Have you tried different known good RAM?

cyclone3d wrote:

Maybe a stick of RAM is flakey?

Have you tried different known good RAM?

sure, this was one of my first troubleshooting steps. tried with different combinations, all tested with memtest. : (

Did you try a different mouse and again with no mouse at all?

Also, is your IBM 5x86 chip on an interposer that is dropping the voltage to 3.45 V? If not, did your ISA board have a voltage regulator to drop the voltage from 5 V to ~3.45 V?

It is unfortuntate that the FSB frequency name wasn't standardised among motherboard manufacturers. I think on PCI boards, "PCLK" is PCI-CLOCK, and the ISA clocks are derived from the PCI clock (at least as viewed from the BIOS), rather than the FSB.

Might be worth running MEMTEST+ 4.00 (not the newer ones).

Helps to take photos as well. Are you using single or double banked cache? 512K or 256K? And could you be using EDO RAM when it wants FPM?

hello,

so i got distracted by life stuff.. then a few days ago i got back to this project and tried a different approach. instead of blaming it on hardware, i tried it with a completely fresh install. turns out it was the system files that were the problem - they got so corrupted that launching any application resulted in further random corruptin. so even when i booted from a floppy everything was a mess.

this might have started with the overclocked cyrix processor freezing on boot, or a hundred other reasons. the takeaway is one shouldn't blame stuff on hardware before every software possibility is exhausted.

It is also possible that hardware run out of specification or in conflict is corrupting your software and your problem may slowly return. I've certainly run into this a few times.