[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [RFC v2] ARM VM System Specification



Il 10/06/2014 20:08, Peter Maydell ha scritto:
On 10 June 2014 18:04, Christopher Covington <cov@xxxxxxxxxxxxxx> wrote:
On 06/10/2014 10:42 AM, Peter Maydell wrote:
I just noticed that this doesn't mandate that the platform
provides an RTC. As I understand it, the UEFI spec mandates
that there's an RTC (could somebody more familiar with UEFI
than me confirm/deny that?) so we should probably put one here.

Pardon my ignorance, but what exactly disqualifies Generic Timer
implementations from being used as Real Time Clocks?

So my naive view was that an RTC actually had to have
support for dealing with real (wall) clock time, ie
knowing it's 2014 and not 1970. The generic timers are
just timers. Or am I wrong and UEFI doesn't really
require that?

The real-time clock provides four UEFI runtime services (GetTime, SetTime, GetWakeupTime, SetWakeupTime). The spec says that you can return EFI_DEVICE_ERROR from GetTime/SetTime if "the time could not be retrieved/set due to a hardware error", but I don't think this is enough to make these two optional. By comparison, GetWakeupTime/SetWakeupTime can also return EFI_UNSUPPORTED.

So I agree that the RTC is required in UEFI.

Paolo

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel


 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.