diff options
Diffstat (limited to '')
| -rw-r--r-- | Documentation/arch/ia64/efirtc.rst | 144 |
1 files changed, 0 insertions, 144 deletions
diff --git a/Documentation/arch/ia64/efirtc.rst b/Documentation/arch/ia64/efirtc.rst deleted file mode 100644 index fd83284083..0000000000 --- a/Documentation/arch/ia64/efirtc.rst +++ /dev/null @@ -1,144 +0,0 @@ -========================== -EFI Real Time Clock driver -========================== - -S. Eranian <eranian@hpl.hp.com> - -March 2000 - -1. 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. - -2. 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. - - -3. 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. - -4. 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_WKALM_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. - -5. References -============= - -Checkout the following Web site for more information on EFI: - -http://developer.intel.com/technology/efi/ |