Unspecified MPUs checklist
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: STM32MP135F Rev.A NOTICE: Model: STMicroelectronics STM32MP135F-DK Discovery Board NOTICE: Board: MB1635 Var1.0 Rev.A-01 INFO: Reset reason (0x1830): INFO: System exits from STANDBY INFO: PMIC version = 0x21 INFO: Using SDMMC INFO: Instance 1 INFO: Boot used partition fsbl1 NOTICE: BL2: v2.4-stm32mp13-r2.0 NOTICE: BL2: Built : 16:43:51, Nov 17 2020 INFO: BL2: Doing platform setup INFO: RAM: DDR3-1066 bin F 1x4Gb 533MHz v1.53 INFO: BL2: Loading image id 31 INFO: Loading image id=31 at address 0x30006000 INFO: Image id=31 loaded: 0x30006000 - 0x30006246 NOTICE: BL2: Booting BL32 INFO: Entry point address = 0xde209d00 INFO: SPSR = 0x1d3 I/TC: Resumed [ 154.701545] usb usb2: root hub lost power or was reset [ 155.053078] usb 2-1: reset high-speed USB device number 2 using ehci-platform [ 155.055443] stm32-dwmac 5800a000.eth1 eth0: configuring for phy/rmii link mode [ 155.086071] dwmac4: Master AXI performs any burst length [ 155.086119] stm32-dwmac 5800a000.eth1 eth0: No Safety Features support found [ 155.089853] stm32-dwmac 5800e000.eth2 eth1: configuring for phy/rmii link mode [ 155.147488] dwmac4: Master AXI performs any burst length [ 155.147530] stm32-dwmac 5800e000.eth2 eth1: No Safety Features support found [ 155.377627] OOM killer enabled. [ 155.377652] Restarting tasks ... done. [ 155.460869] PM: suspend exit
See [3] for more about rtcwake settings.
5. References[edit source]