Re: [Qemu-devel] [PATCH 3/3] stop the periodic RTC update timer

[Marcelo Tosatti]

On Thu, Jan 12, 2012 at 12:00:06AM +0000, Zhang, Yang Z wrote:
> > -----Original Message-----
> > From: Marcelo Tosatti [mailto:address@hidden
> > 
> > Regarding the UIP bit, a guest could read it in a loop and wait for the 
> > value to
> > change. But you can emulate it in cmos_ioport_read by reading the host time,
> > that is, return 1 during 244us, 0 for remaining of the second, and have 
> > that in sync
> > with update-cycle-ended interrupt if its enabled.
> Yes. Guest may use the loop to read RTC, but the point is the guest is 
> waiting for the UIP changed to 0. If this bit always equal to 0 , guest will 
> never go into the loop. For real RTC, this may wrong, because the RTC cannot 
> give you the valid value during the update cycle. But the virtual RTC 
> doesn't' need this logic, whenever you read it, it will always return the 
> right value to you.

Can't it wait a change from 0 to 1?