5x86 Upgrade Project

[Agent Orange]

Need another opinion (or so):

Today I installed a Am5x86-P75 (AMD-5x-133 ADW) in my Gigabyte 486VF mobo. After much jumper switching, I finally got it to crank out 132 MHz, and it seems to run fine. What I'm not sure of is the AT Bus Clock Settings. The CPU is jumpered to the"DX4" setting; i.e. 33 Mhz CPU clock/100 MHz CPU Frequency (the only configuation that will give me 132 MHz).

The mobo's available AT Bus Clock settings are as follows:

* 1/3 CLKIN for 25 MHz System
* 1/4 CLKIN for 33 MHz System
* 1/5 CLKIN for 40 MHz System
* 1/6 CLKIN for 50 MHz System

I'm currently using "1/6 CLKIN". The only reference on this particular cpu is the from the following URL:

http://web.inter.nl.net/hcc/J.Steunebrink/amd5x86.htm

What say you?

 

[Raven]

That's an odd reference. I'd wager that CLKIN means "Clock Input" and since it's giving you fractions I'd say that this board must be using a divider on a clock crystal to achieve various speeds. With that said, I'd imagine your CPU *should* have been running at 200Mhz with that bus setting, i.e., 50Mhz*4. The Am5x86 has a static multiplier of 4x (unless overridden by something - they're intended for 33Mhz bus speeds to achieve 133Mhz with that 4x) if I recall, so perhaps you are running it at ~2.5x50Mhz with some board setting? It's well possible, given good cooling and voltage, and a good board. A popular overclock was to get Am5x86 chips up to 160Mhz by using a 40Mhz bus. What are you using to measure CPU speed? I use CHKCPU, and it is quite accurate in reading the speed raw - it doesn't rely on preconceived information about how fast the chip *should* be, etc.

This is all conjecture, so forgive me if I'm incorrect.

Edit: Ironically the linked reference page is also the author of CHKCPU.. xD

 

[Agent Orange]

That's an odd reference. I'd wager that CLKIN means "Clock Input" and since it's giving you fractions I'd say that this board must be using a divider on a clock crystal to achieve various speeds. With that said, I'd imagine your CPU *should* have been running at 200Mhz with that bus setting, i.e., 50Mhz*4. The Am5x86 has a static multiplier of 4x (unless overridden by something - they're intended for 33Mhz bus speeds to achieve 133Mhz with that 4x) if I recall, so perhaps you are running it at ~2.5x50Mhz with some board setting? It's well possible, given good cooling and voltage, and a good board. A popular overclock was to get Am5x86 chips up to 160Mhz by using a 40Mhz bus. What are you using to measure CPU speed? I use CHKCPU, and it is quite accurate in reading the speed raw - it doesn't rely on preconceived information about how fast the chip *should* be, etc.

This is all conjecture, so forgive me if I'm incorrect.

Edit: Ironically the linked reference page is also the author of CHKCPU.. xD

I haven't use any software yet to determine the cpu speed. This BIOS gives you the cpu speed and amount of memory on POST. I doubt that I'll see 200 MHz with this board but I'd take it if I could get it. I'll run some software tests tonught and see what happens. Also CLKIN is the timer for the the bus.

 

[Anonymous Coward]

Use 1/4 CLKIN. Your bus speed is 33MHz. If you divide by 4, you get approximately 8MHz, which is the ISA standard. If you divide by 6, you are actually underclocking your cards.

 

[Agent Orange]

Use 1/4 CLKIN. Your bus speed is 33MHz. If you divide by 4, you get approximately 8MHz, which is the ISA standard. If you divide by 6, you are actually underclocking your cards.

I'll try that too. What's confusing is the 5x86 is actually quadrupling the base 33 MHz (4 x 33 = 132). I'm seeing 133.4 MHz with CHKCPU v1.6. So, I'll set the AT bus to CLKIN 1/4 and see what happens. Thanks for the tip!

Edit: Works great!