Re: [Xen-devel] RE: A question about PIT platform timer

[Keir Fraser <keir@xxxxxxxxxxxxx>]

On 11/12/06 12:10, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

> Yes, there's no interrupt from it. But what's the known frequency?
> CALIBRATE_LATCH or CLOCK_TICK_RATE? platform_timer_scale
> is set to the later, and so ch2 needs to work on same frequency or
> else count value will result incorrect offset. However I didn't see such
> setting on ch2. Does I miss something? :-)

All the PIT channels tick at CLOCK_TICK_RATE. Mode-0 is not auto-relatching,
so when the counter reaches 0000 it carries on FFFF, FFFE, FFFD, ....

So we calculate platform system time as:
 system_timestamp + (pit_timestamp - pit_timenow) * (delta_system/delta_pit)

 -- Keir


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel