# HPET hardware support ?

## Anon5710

Alright, long time ago i posted a message here  :Smile: 

I'm running the ubuntu  live-cd on  a small board ESM-945ETX (this is an embedded board) http://www.avalue.com.tw/products/ESM-945ETX.cfm

So about HPET, i can't figure out if it is supported or not.

```
ubuntu@ubuntu:~$ dmesg | grep hpet

[    0.184674] hpet clockevent registered

[    0.184760] hpet0: at MMIO 0xfed00000, IRQs 2, 8, 0

[    0.184993] hpet0: 3 comparators, 64-bit 14.318180 MHz counter

[    0.188067] Switching to clocksource hpet

[    3.798968] rtc0: alarms up to one day, 114 bytes nvram, hpet irqs

ubuntu@ubuntu:~$ 
```

However running acpidump to dump my ACPI tables and iasl to decompile them, i do not find any reference to hpet.

So i find it strange that this live cd can find it, acording the hpet specs. The base adress should be reported by the bios aml tabels (ACPI DSDT table), but this adress isn't availabel in the decompiled asl file !

So does this embedded board have hpet support or not ?

Any sure fire way i can find out ?[/u]

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## Ant P.

If the kernel doesn't crash instantly when it switches to hpet, then it has one.

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## Anon5710

So, how does Linux finds the HPET device ?

It can't use the acpi tabels, because the device isn4t listed there.

Is it possibel that Linux reports HPET but actualy uses an other clocksource ?

(Windows XP did this.)

Regards,

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## Ant P.

The kernel has code to force-enable a HPET at a hardcoded address in arch/x86/kernel/quirks.c, it matches the address in your dmesg output so that's a possibility.

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## roarinelk

ACPI has a "HPET" table; on systems without it sometimes the kernel knows where 

the HPET is and force-enables it.   The HPET is overrated anyway.

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## Anon5710

Thanks that was helpfull information !

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## _______0

```
cat /sys/devices/system/clocksource/clocksource0/available_clocksource
```

and to check which one is being used:

```
cat /sys/devices/system/clocksource/clocksource0/current_clocksource
```

apparently acpi_pm si better than hpet nowadays. I read this reading about realtime kernel for audio.

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