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1 Purpose[edit source]
This article describes how to use the RTC.
2 How to set a hardware clock using the hwclock tool[edit source]
The correct system time must first be set with the date command. Type the date command to see the date and time format of the string:
date Fri Mar 9 12:18:51 UTC 2018
date --set="Fri Mar 9 19:18:51 UTC 2018" Fri Mar 9 19:18:51 UTC 2018
Set the hardware clock to this date:
hwclock Fri Mar 9 12:21:03 2018 0.000000 seconds hwclock --systohc --utc hwclock Fri Mar 9 19:19:52 2018 0.000000 seconds
See [1] for more about date settings. See [2] for more about hwclock settings.
3 How to set an alarm[edit source]
# disable the alarm
echo 0 > /sys/class/rtc/rtc0/wakealarm
# calculate alarm with 1 minute later
wakeuptime=`date -d "1 minute" +%s`
# set the alarm
echo $wakeuptime > /sys/class/rtc/rtc0/wakealarm
root@stm32mp1:~# [ 829.279019] rtc rtc0: Alarm occurred
You can also set an alarm 'n' seconds later:
echo +10 > /sys/class/rtc/rtc0/wakealarm
4 How to set an alarm and go into a system sleep state with the rtcwake tool[edit source]
# calculate an alarm 1 minute later
wakeuptime=`date -d "1 minute" +%s`
# set wakeup on /dev/rtc0 rtcwake -lt$wakeuptime -m mem rtcwake: wakeup from "mem" using /dev/rtc0 at Sun Mar 11 10:48:06 2018 [ 154.022303] PM: suspend entry (deep) [ 154.024421] PM: Syncing filesystems ... done. [ 154.037258] Freezing user space processes ... (elapsed 0.001 seconds) done. [ 154.044397] OOM killer disabled. [ 154.047555] Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done. [ 154.055039] Suspending console(s) (use no_console_suspend to debug)
One minute later...
NOTICE: CPU: STM32MP157CAA Rev.B NOTICE: Model: STMicroelectronics STM32MP157C eval daughter on eval mother NOTICE: Board: MB1263 Var1 Rev.C-01 INFO: Reset reason (0x810): INFO: System exits from STANDBY INFO: Using SDMMC INFO: Instance 1 INFO: Boot used partition fsbl1 INFO: Product_below_2v5=1: HSLVEN update is INFO: destructive, no update as VDD>2.7V NOTICE: BL2: v2.0(debug):v2.0-stm32mp-19-01-29 NOTICE: BL2: Built : 15:58:42, Jan 29 2019 INFO: BL2: Doing platform setup INFO: PMIC version = 0x10 INFO: RAM: DDR3-1066/888 bin G 2x4Gb 533MHz v1.41 INFO: BL2 runs SP_MIN setup INFO: BL2: Loading image id 4 INFO: Loading image id=4 at address 0x2ffe5000 INFO: Image id=4 loaded: 0x2ffe5000 - 0x30000000 INFO: BL2: Skip loading image id 5 INFO: read version 0 current version 0 NOTICE: BL2: Booting BL32 INFO: Entry point address = 0x2ffe5000 INFO: SPSR = 0x1d3 INFO: PMIC version = 0x10 NOTICE: SP_MIN: v2.0(debug):v2.0-stm32mp-19-01-29 NOTICE: SP_MIN: Built : 15:58:42, Jan 29 2019 INFO: ARM GICv2 driver initialized INFO: stm32mp HSI (18): Secure only INFO: stm32mp HSE (20): Secure only INFO: stm32mp PLL2 (27): Secure only INFO: stm32mp PLL2_R (30): Secure only INFO: SP_MIN: Initializing runtime services INFO: SP_MIN: Preparing exit to normal world [ 154.074319] dwc2 49000000.usb-otg: suspending usb gadget configfs-gadget [ 154.196804] Disabling non-boot CPUs ... [ 154.250046] CPU1 killed. [ 154.251704] Enabling non-boot CPUs ... [ 154.252697] CPU1 is up [ 154.254885] rtc rtc0: Alarm occurred [ 154.273940] dwmac4: Master AXI performs any burst length [ 154.273972] stm32-dwmac 5800a000.ethernet eth0: No Safety Features support found [ 154.276938] usb usb2: root hub lost power or was reset [ 154.284703] dwc2 49000000.usb-otg: resuming usb gadget configfs-gadget [ 154.491151] dwc2 49000000.usb-otg: new device is high-speed [ 154.619589] dwc2 49000000.usb-otg: new device is high-speed [ 154.669343] usb 2-1: reset high-speed USB device number 2 using ehci-platform [ 154.697272] dwc2 49000000.usb-otg: new address 2 [ 154.722774] configfs-gadget gadget: high-speed config #1: c [ 155.066198] OOM killer enabled. [ 155.069339] Restarting tasks ... done. [ 155.075470] PM: suspend exit
See [3] for more about rtcwake settings.
5 References[edit source]