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

[Zhang, Yang Z]

> -----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.

best regards
yang