rtc(7) INTERACTIVE UNIX System rtc(7)
NAME
rtc - real time clock interface
DESCRIPTION
The rtc driver supports the real time clock chip, allowing
it to be set with the correct local time, and allowing the
time to be read from the chip.
Ioctl Calls
RTCRTIME
This call is used to read the local time from the real
time clock chip. The argument to the ioctl is the
address of a buffer of RTCNREG unsigned characters
(RTCNREG is defined is <sys/rtc.h>). The ioctl will
fill in the buffer with the contents of the chip regis-
ters. Currently, RTCNREG is 14, and the meanings of
the byte registers are as follows:
______________________________
| Register| Contents |
|_________|___________________|
| 0 | Seconds |
| 1 | Second alarm |
| 2 | Minutes |
| 3 | Minute alarm |
| 4 | Hours |
| 5 | Hour alarm |
| 6 | Day of week |
| 7 | Date of month |
| 8 | Month |
| 9 | Year |
| A | Status register A|
| B | Status register B|
| C | Status register C|
| D | Status register D|
|_________|___________________|
For further information on the functions of these
registers, see the IBM Personal Computer AT Technical
Reference.
RTCSTIME
This call is used to set the time into the real time
clock chip. The argument to the ioctl is the address
of a buffer of RTCNREGP unsigned characters (RTCNREGP
is defined is <sys/rtc.h>.) These bytes should be the
desired chip register contents. Currently, RTCNREGP is
10, representing registers 0-9 as shown above. Note
that only user root (the superuser) may open the real-
time clock device for writing, and that the RTCSTIME
ioctl will fail for any user other than root.
Rev. 1.3 Page 1
rtc(7) INTERACTIVE UNIX System rtc(7)
FILES
/dev/rtc
ADDED VALUE
This entry, supplied by INTERACTIVE Systems Corporation,
contains enhancements to UNIX System V.
Rev. 1.3 Page 2