last change: 27.08.2001

since 16.9.2000

A7V Troubleshooting
Why the heck is there a tank ?!?

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Why was CPU HLT disabled from BIOS 1004 on? Should I reenable it ?

What is CPU HLT ?

In A7V BIOS Version 1003 the CPU was considerably cooler when idling (doing nothing) than in all newer versions. This was due to the fact that this version allowed the CPU to be stopped via the HLT function. If it had nothing to do, it would be stopped and consume less power, generating less heat.

You may read more on this behaviour in the article Temperature Issue.

What happens when HLT is active ?

The CPU only draws very little current while it is in HLT mode. The value depends on CPU type, frequency and voltage, but may be somewhere around 10A. As soon as the CPU gets some work again, it leaves HLT mode and begins drawing the normal amount of current, somewhere around 30-40A.

Why was HLT disabled ?

When leaving HLT mode the CPU draws the higher current instantly. The onboard voltage regulator has to keep the CPU's core voltage (Vcore) steady. When the load shifts (meaning the current drawn is variated) it has to re-regulate Vcore to get it back into the limits allowed for the CPU. Now, if there is such a load shift as from 10A to 40A almost instantly, the voltage regulator struggles to keep the voltage, but for a very short time can't do so. This is directly after the load shift. Depending on the CPU and many other factors, the resulting wrong voltage (too low or too high), if only present for a few fractions of a second, can lead to a system crash. This is what you see as a lockup, reboot or simply a blue screen.

Although this link is in german, it supports what is written here:ASUS Germany FAQ

So, if HLT is disabled, the CPU draws more current while idle. The load shift when it gets back to work is significantly smaller, let's say from 30A to 40A. Thus, disabling HLT makes a mainboard a lot more stable, especially when it's equipped with a mediocre voltage regulator. Many AMD mainboards use very mediocre voltage regulators. The A7V for has only a 2 stage regulator as opposed to potentially better 3 stage regulators on other mainboards. I can't comment on the A7V regulator's quality, though. Being 2 stage does not automatically mean it's bad...

Should I reenable HLT ?

This depends on what you want.

Leave HLT disabled for a more stable System.

Enable HLT for a longer CPU Life. Remember, for electronic components 7 to 10 °C more temperature (constantly) mean half life time !

If you want to reenable HLT, use a special BIOS by Braziliantech, use the register hack described in Reenabling Idle mode, or use a (working!) software cooling programm.

What to do ?

I prefer a stable System any day, so I recommend leaving HLT disabled. This means simply use a BIOS newer than 1003, if possible the most recent one (1008 as of today). Don't use the register hack and don't use any software cooling (including the one in ASUS probe)

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