Difference between revisions of "RTC"

Revision as of 16:00, 26 August 2009

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

Hardware

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.

Driver installation

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)

Usage

• From U-Boot there is a command date to read, reset, update the RTC.

 BIOS> help date          for more information
 BIOS> date reset         to be done after battery exchange to remove message '''### Warning: RTC oscillator has stopped'''
 BIOS> date 013122302007  to set the date January 31th 2007 22h30.

• From Linux use the command hwclock to read, write, synchronize the RTC:

 # hwclock --help
 # hwclock -r      to read hardware clock and print result
 # hwclock -s      to set the system time from the hardware RTC clock
 # hwclock -w      to set the hardware RTC clock to the current system time

• 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 013122302007  to sets the system date january 31th 2007 22h30.

• Then, when booting you will see something like this:

 ds1374 0-0068: setting the system clock to 2007-09-09 17:35:51 (1189359351)

Links

• Maxim's DS1374 datasheet