RTC
On this page, you will find useful informations to use the Real Time Clock of your boards (if chip is mounted).
Contents
Hardware
APF9328/APF27
No permanent RTC is present on the APF9328/APF27 modules, but you can have one (as an option) on the development boards or add it yourself if you are an electrician (it is not so complex to add a DS1374 (with integrated quartz) on the I2C bus). Do not forget to provide the two power-supply (VCC and Vbackup)). Currently only Maxim's DS1374 has been used but any I2C RTC, supported by Linux, should work the same way.
APF51/APF28
APF51 and APF28 modules have an onboard PMIC with an integrated RTC.
Driver installation
APF9328/APF27
DS1374 is by default included in standard Armadeus Linux kernel. To check if your board (Linux) has correctly detected the RTC:
# dmesg | grep ds1374 ds1374-legacy 0-0068: chip found, driver version 1.0 ds1374-legacy 0-0068: rtc core: registered ds1374-legacy as rtc0 ds1374-legacy 0-0068: setting system clock to 1970-01-01 00:00:07 UTC (7)
APF51
Driver is by default installed and launched. To check if your board (Linux) has correctly detected the RTC:
# dmesg | grep rtc wm831x-rtc wm831x-rtc: rtc core: registered wm831x as rtc0 wm831x-rtc wm831x-rtc: setting system clock to 2011-05-03 13:27:26 UTC (1304429246)
APF28
On APF28 the RTC is integrated under the i.MX28 processor. See the reference manual chapter 22 "Real-Time Clock Alarm Watchdog Persistent Bits".
There isn't button-lithium backup battery under APF28dev board, if we unplug the power, clock is not saved and then we could ask : what the interest of RTC if not backuped ?
The interest is when we power the whole board with a battery and we poweroff the apf28 with the command :
$ poweroff
The processor will be powered of ... except the RTC. Then we could power on the board pushing power switch and keep the clock up to date.
 |
Warning: To enable poweroff on APF28dev the board must be powered by battery (J10 pin 4) and the USB-powering must be disconnected. To disconnect it, just unsolder the self L7 (behind the usb J3 connector) |
 |
Note: Currently, the clock doesn't work in poweroff it must be fixed. The date and hour are keeped but not incremented |
Clock
To read the hardware value of clock use hwclock command on file /dev/rtc0:
Keep clock
To power off the board type :
# poweroff The system is going down NOW! Sent SIGTERM to all processes Sent SIGKILL to all processes P Communications disconnect (Back at localhost) ---------------------------------------------------- (/home/fabien/) C-Kermit>
And to wake-up the board push the button 'ON'. The date and hour will be keeped when you type 'date' or 'hwclock'.
Usage
| |
Note: We recommand to store time in UTC format in the RTC; that will ease the timezone/summer time handling. |
- From Linux use the command hwclock to read, write, synchronize the RTC (here we pre-suppose that RTC is storing time in UTC format).
# hwclock --help # hwclock -r -u to read hardware clock and print result (localtime) # hwclock -s -u to set the system time from the hardware clock # hwclock -w -u to set the hardware clock to the current system time (UTC)
| |
Warning: Security "features" prevent to change RTC time more than 8 times per hour on the APF51 !! |
- and date to read and update system date and time while running:
# date --help for more information # date -R to read hardware clock and print result # date 013122302011 to sets the system date to january 31th 2011 22h30 (localtime) # date 2011.01.31-22:30:00 also do the job
- Then, when booting you will see something like this:
ds1374 0-0068: setting the system clock to 2011-xxxx or wm831x-rtc wm831x-rtc: setting system clock to 2011-xxxx
- TimeZone/Summer time handling can be configured in /etc/TZ:
# cat /etc/TZ CET-1DST,M3.5.0/2:00,M10.5.0/3:00
- you can update RTC from a NTP (Network Time Protocol) server if your board is connected to internet or a NTP server
# ntpd -nqp 217.147.208.1 ntpd: setting clock to Mon Apr 23 22:36:39 DST 2012 (offset 1335216961.855897s) # hwclock -wu # to set the hardware clock to the current system time (UTC)
