VirtualBox HPET Problems
Posted: Wed May 04, 2016 11:30 am
Hello!
Recently, i've been trying to get the HPET to work properly as a source for event timing in my kernel. As much as I love the PIT, I'd like something with a little more precision (and the ability to provide a stable time source).
It took me a couple of tries to figure it out, but my HPET code seems to work reliably in VMWare. The problem is that it fails silently while running in VirtualBox. I was wondering if anybody else has tried to do this on vbox and succeeded.
What i'm trying to do is set up a one-shot interrupt from the HPET to trigger a timer callback. VirtualBox is reporting an HPET via ACPI, and the information i'm getting seems to be sane. I've made sure my I/O APIC mapping is set up properly, and i'm using level triggered interrupts. ( This is so that i can detect an overrun of the HPET timer beyond my intended interrupt time, supposing the delta between the time that was current during delta calculation and the time that i set the HPET counter enabled was smaller than the actual time that passed ).
I have the comparator already set up as 32-bit, level triggered, interrupts disabled.
Every time I set the HPET counter comparator to trigger, i do these steps (which took some trial and error to figure out, as the HPET specification is somewhat ambiguous:
source file
If the naming here isn't obvious, what i'm doing here is enabling the comparator write, writing the comparator (32 bits, because this is an x86 kernel), clearing the interrupt level, and then enabling interrupts from the counter.
Like I said before, this works perfectly fine in VMWare, which i usually trust to be more accurate and more quick-to-fail on problems, but seems to just not work in virtualbox. I'm really stuck here, and at the moment, I don't have hardware I feel comfortable testing on, so any help here would be greatly appreciated.
Recently, i've been trying to get the HPET to work properly as a source for event timing in my kernel. As much as I love the PIT, I'd like something with a little more precision (and the ability to provide a stable time source).
It took me a couple of tries to figure it out, but my HPET code seems to work reliably in VMWare. The problem is that it fails silently while running in VirtualBox. I was wondering if anybody else has tried to do this on vbox and succeeded.
What i'm trying to do is set up a one-shot interrupt from the HPET to trigger a timer callback. VirtualBox is reporting an HPET via ACPI, and the information i'm getting seems to be sane. I've made sure my I/O APIC mapping is set up properly, and i'm using level triggered interrupts. ( This is so that i can detect an overrun of the HPET timer beyond my intended interrupt time, supposing the delta between the time that was current during delta calculation and the time that i set the HPET counter enabled was smaller than the actual time that passed ).
I have the comparator already set up as 32-bit, level triggered, interrupts disabled.
Every time I set the HPET counter comparator to trigger, i do these steps (which took some trial and error to figure out, as the HPET specification is somewhat ambiguous:
source file
Code: Select all
::HW::ACPI::HPET :: SetCounterComparratorWritable ( & CounterInfo, true );
::HW::ACPI::HPET :: WriteCounterComparrator32 ( & CounterInfo, NextInternalTimeout );
::HW::ACPI::HPET :: ClearCounterInterruptLevel ( & CounterInfo );
::HW::ACPI::HPET :: SetCounterEnabled ( & CounterInfo, true );
Like I said before, this works perfectly fine in VMWare, which i usually trust to be more accurate and more quick-to-fail on problems, but seems to just not work in virtualbox. I'm really stuck here, and at the moment, I don't have hardware I feel comfortable testing on, so any help here would be greatly appreciated.
