PIT Channel 0 Example Code @ Wiki

[Bughunter]

http://www.osdev.org/mediawiki/index.ph ... ample_Code

I recently setup my exception handlers and I have setup the PIT IRQ.

Now, I was wondering how could I accurately calculate how many fractions of an mS and how many mS should I add to the system timer each time the IRQ fires?

I tried looking at the code example, but for some reason I don't really get why 2^32 and 256 is used everywhere (I do understand why the example uses 3579545/3 though). Maybe coffee level dropped too low or I didn't sleep enough, but I'm not getting it at the moment.

Anyone want to look at it and perhaps post their thoughts?

[os64dev]

you dont time with PIT, you do the time the realtime clock. It is designed for it and has a 1ms accuracy. or the local apic for that matter.

[Bughunter]

But in many topics I read here, the PIT IRQ is used to measure time. And by reading the code example, I assume the code example uses it for the system timer too?

Btw, any info on how to access the RTC?

[Brendan]

Hi,

I tried looking at the code example, but for some reason I don't really get why 2^32 and 256 is used everywhere (I do understand why the example uses 3579545/3 though). Maybe coffee level dropped too low or I didn't sleep enough, but I'm not getting it at the moment.

Anyone want to look at it and perhaps post their thoughts?

I took a look - it was unnecessarily complicated and had some bugs. I fixed the bugs and simplified it a little...


Cheers,

Brendan

[Bughunter]

Thanks . I will have a look at it when I have some more time.