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path: root/drivers/rtc/rtc-rx8025.c
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2009-06-18rtc: add stand-alone driver for RX8025 chipWolfgang Grandegger
Add support for the Epson RX-8025SA/NB RTC chips. It includes support for alarms, periodic interrupts (1 Hz) and clock precision adjustment. For clock precision adjustment, the SYSFS file "clock_adjust_ppb" gets created in "/sys/class/rtc/rtcX/device". It permits to set and get the clock adjustment in ppb (parts per billion), e.g.: # echo -183000 > /sys/class/rtc/rtc0/device/clock_adjust_ppb # cat /sys/class/rtc/rtc0/device/clock_adjust_ppb -183000 This allows to compensate temperature dependent clock drifts. According to the RX8025 SA/NB application manual the frequency and temperature characteristics can be approximated using the following equation: df = a * (ut - t)**2 df: Frequency deviation in any temperature a : Coefficient = (-35 +-5) * 10**-9 ut: Ultimate temperature in degree = +25 +-5 degree t : Any temperature in degree Signed-off-by: Wolfgang Grandegger <wg@grandegger.com> Signed-off-by: Sergei Poselenov <sposelenov@emcraft.com> Signed-off-by: Yuri Tikhonov <yur@emcraft.com> Signed-off-by: Dmitry Rakhchev <rda@emcraft.com> Signed-off-by: Matthias Fuchs <matthias.fuchs@esd.eu> Acked-by: Jean Delvare <khali@linux-fr.org> Signed-off-by: Alessandro Zummo <a.zummo@towertech.it> Cc: David Brownell <david-b@pacbell.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>