mirror of
https://github.com/torvalds/linux.git
synced 2024-11-08 21:21:47 +00:00
670e9f34ee
Remove many duplicated words under Documentation/ and do other small
cleanups.
Examples:
"and and" --> "and"
"in in" --> "in"
"the the" --> "the"
"the the" --> "to the"
...
Signed-off-by: Paolo Ornati <ornati@fastwebnet.it>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
129 lines
4.3 KiB
Plaintext
129 lines
4.3 KiB
Plaintext
EFI Real Time Clock driver
|
|
-------------------------------
|
|
S. Eranian <eranian@hpl.hp.com>
|
|
March 2000
|
|
|
|
I/ Introduction
|
|
|
|
This document describes the efirtc.c driver has provided for
|
|
the IA-64 platform.
|
|
|
|
The purpose of this driver is to supply an API for kernel and user applications
|
|
to get access to the Time Service offered by EFI version 0.92.
|
|
|
|
EFI provides 4 calls one can make once the OS is booted: GetTime(),
|
|
SetTime(), GetWakeupTime(), SetWakeupTime() which are all supported by this
|
|
driver. We describe those calls as well the design of the driver in the
|
|
following sections.
|
|
|
|
II/ Design Decisions
|
|
|
|
The original ideas was to provide a very simple driver to get access to,
|
|
at first, the time of day service. This is required in order to access, in a
|
|
portable way, the CMOS clock. A program like /sbin/hwclock uses such a clock
|
|
to initialize the system view of the time during boot.
|
|
|
|
Because we wanted to minimize the impact on existing user-level apps using
|
|
the CMOS clock, we decided to expose an API that was very similar to the one
|
|
used today with the legacy RTC driver (driver/char/rtc.c). However, because
|
|
EFI provides a simpler services, not all ioctl() are available. Also
|
|
new ioctl()s have been introduced for things that EFI provides but not the
|
|
legacy.
|
|
|
|
EFI uses a slightly different way of representing the time, noticeably
|
|
the reference date is different. Year is the using the full 4-digit format.
|
|
The Epoch is January 1st 1998. For backward compatibility reasons we don't
|
|
expose this new way of representing time. Instead we use something very
|
|
similar to the struct tm, i.e. struct rtc_time, as used by hwclock.
|
|
One of the reasons for doing it this way is to allow for EFI to still evolve
|
|
without necessarily impacting any of the user applications. The decoupling
|
|
enables flexibility and permits writing wrapper code is ncase things change.
|
|
|
|
The driver exposes two interfaces, one via the device file and a set of
|
|
ioctl()s. The other is read-only via the /proc filesystem.
|
|
|
|
As of today we don't offer a /proc/sys interface.
|
|
|
|
To allow for a uniform interface between the legacy RTC and EFI time service,
|
|
we have created the include/linux/rtc.h header file to contain only the
|
|
"public" API of the two drivers. The specifics of the legacy RTC are still
|
|
in include/linux/mc146818rtc.h.
|
|
|
|
|
|
III/ Time of day service
|
|
|
|
The part of the driver gives access to the time of day service of EFI.
|
|
Two ioctl()s, compatible with the legacy RTC calls:
|
|
|
|
Read the CMOS clock: ioctl(d, RTC_RD_TIME, &rtc);
|
|
|
|
Write the CMOS clock: ioctl(d, RTC_SET_TIME, &rtc);
|
|
|
|
The rtc is a pointer to a data structure defined in rtc.h which is close
|
|
to a struct tm:
|
|
|
|
struct rtc_time {
|
|
int tm_sec;
|
|
int tm_min;
|
|
int tm_hour;
|
|
int tm_mday;
|
|
int tm_mon;
|
|
int tm_year;
|
|
int tm_wday;
|
|
int tm_yday;
|
|
int tm_isdst;
|
|
};
|
|
|
|
The driver takes care of converting back an forth between the EFI time and
|
|
this format.
|
|
|
|
Those two ioctl()s can be exercised with the hwclock command:
|
|
|
|
For reading:
|
|
# /sbin/hwclock --show
|
|
Mon Mar 6 15:32:32 2000 -0.910248 seconds
|
|
|
|
For setting:
|
|
# /sbin/hwclock --systohc
|
|
|
|
Root privileges are required to be able to set the time of day.
|
|
|
|
IV/ Wakeup Alarm service
|
|
|
|
EFI provides an API by which one can program when a machine should wakeup,
|
|
i.e. reboot. This is very different from the alarm provided by the legacy
|
|
RTC which is some kind of interval timer alarm. For this reason we don't use
|
|
the same ioctl()s to get access to the service. Instead we have
|
|
introduced 2 news ioctl()s to the interface of an RTC.
|
|
|
|
We have added 2 new ioctl()s that are specific to the EFI driver:
|
|
|
|
Read the current state of the alarm
|
|
ioctl(d, RTC_WKLAM_RD, &wkt)
|
|
|
|
Set the alarm or change its status
|
|
ioctl(d, RTC_WKALM_SET, &wkt)
|
|
|
|
The wkt structure encapsulates a struct rtc_time + 2 extra fields to get
|
|
status information:
|
|
|
|
struct rtc_wkalrm {
|
|
|
|
unsigned char enabled; /* =1 if alarm is enabled */
|
|
unsigned char pending; /* =1 if alarm is pending */
|
|
|
|
struct rtc_time time;
|
|
}
|
|
|
|
As of today, none of the existing user-level apps supports this feature.
|
|
However writing such a program should be hard by simply using those two
|
|
ioctl().
|
|
|
|
Root privileges are required to be able to set the alarm.
|
|
|
|
V/ References.
|
|
|
|
Checkout the following Web site for more information on EFI:
|
|
|
|
http://developer.intel.com/technology/efi/
|