Difference between revisions of "RTC"

Revision as of 18:12, 6 December 2008

On this page, you will find usefull informations to use an external DS1374 Real Time Clock. This feature apply to the armadeus software release 2.0 and above.

Hardware

No permanent RTC is present on the APF9328 but 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).

Configuration

First be sure to use an armadeus 2.0 or higher. The RTC/DS1374 support is already configured in U-BOOT and linux kernel 2.6.18.1 and higher. Therefore you have nothing to configure to use the RTC. Nevertheless these are the parameters to check to have the RTC supported:

$ make linux26-menuconfig

• check the i2c module drivers "I2C support", "I2C DEVICE", "I2C HARDWARE/bus on imx"
• check the RTC module driver "RTC class", "set time from RTC" "RTC interface dev"
• if you integrates these module statically in the kernel then the system date will be set at power-up.

$ make

and reload your kernel and/or rootfs

Installation

• Installation is automatic with the default configuration but if you choose to compile rtc and i2c drivers as module then you have to load them:

$ modprobe i2c-imx
$ modprobe rtc-ds1374
$ modprobe rtc-dev

• you will get something like this :

$ dmesg | grep rtc
<6>ds1374 0-0068: rtc intf: sysfs
<6>ds1374 0-0068: rtc intf: proc
<6>ds1374 0-0068: rtc intf: dev (254:0)
<6>ds1374 0-0068: rtc core: registered ds1374 as rtc0

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 commande 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-ic ds1374 datasheet http://datasheets.maxim-ic.com/en/ds/DS1374-DS1374U.pdf