Difference between revisions of "RTC"

Revision as of 20:27, 23 April 2012

On this page, you will find useful informations to use the Real Time Clock of your boards (if chip is mounted).

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

APF51 module 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)

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

Links

• Maxim's DS1374 datasheet