Keeping Alive In The Power Off State - Freescale Semiconductor i.MX 6Solo Reference Manual

Driver Features
Besides the initialization function, the SRTC driver provides IOCTL functions to set up
the RTC timers and alarm functions. The following RTC IOCTLs are implemented by the
SRTC driver:
• RTC_RD_TIME
• RTC_SET_TIME
• RTC_AIE_ON
• RTC_AIE_OFF
• RTC_ALM_READ
• RTC_ALM_SET
The driver information can be access by the proc file system. For example:
root@freescale /unit_tests$ cat /proc/driver/rtc
rtc_time : 12:48:29
rtc_date : 2009-08-07
alrm_time : 14:41:16
alrm_date : 1970-01-13
alarm_IRQ : no
alrm_pending : no
24hr : yes

24.2.2 Keeping Alive in the Power Off State

To preserve the time when the device is in the power-off state, the SRTC clock source
should be set to CKIL and the voltage input, NVCC_SRTC_POW, should remain active.
Usually these signals are connected to the PMIC and software can configure the PMIC
registers to enable the SRTC clock source and power supply.
Generally, when the main battery is removed and the device is in power-off state, a coin-
cell battery is used as a backup power supply. To avoid SRTC time loss, the voltage of
the coin-cell battery should be sufficient to power the SRTC. If the coin-cell battery is
chargeable, it is recommended to automatically enable the coin-cell charger so that the
SRTC is properly powered.
24.3 Driver Features
• Implementing all the functions required by Linux to provide the real-time clock and
alarm interrupt.
• Reserveing time in power-ff state.
• Alarm wakes up the system from low-power modes.
i.MX 6Solo/6DualLite Linux Reference Manual, Rev. L3.0.35_4.1.0, 09/2013
174 Freescale Semiconductor, Inc.