On Thu, Jan 12, 2012 at 07:59:06AM -0200, Marcelo Tosatti wrote: > On Thu, Jan 12, 2012 at 12:00:06AM +0000, Zhang, Yang Z wrote: > > > -----Original Message----- > > > From: Marcelo Tosatti [mailto:mtosa...@redhat.com] > > > > > > 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?
The point is the guest can use the hardware as it pleases, not only as is suggested in the hardware documentation.
