rtc0, rtc1 assignment in Linux

German Baranov

Intellectual 660 points

Other Parts Discussed in Thread: DM385

Hello!

There are two real time clocks in my DM385 system - omap internal and i2c chip pcf8563.

Linux, when starts, assigns device rtc0 to omap clock and rtc1 to i2c chip.

Where and how is this desided? Can I switch those numbers and make i2c clock to be rtc0?

There are settings in Linux configuration (hctosys) which define from where (rtc0 or rtc1) system loads

time after reset, but can I change devices completely and make i2c chip to be /dev/rtc0 ?

Thanks

German

over 8 years ago

0 Pavel Botev over 8 years ago

TI__Guru**** 170625 points

Hi German,

If you remove the internal RTC driver, then your i2c chip should map on /dev/rtc0. See the below pointers for more info:

processors.wiki.ti.com/.../AM335x_PSP_User's_Guide
linux-kernel/Documentation/rtc.txt
linux-kernel/arch/arm/mach-omap2/devices.c

Regards,
Pavel

0 Pavel Botev over 8 years ago in reply to Pavel Botev

TI__Guru**** 170625 points

German,

It seems to me that internal RTC is mapped/registered to /dev/rtc0 at the below location:

linux-kernel/arch/arm/mach-omap2/devices.c

return platform_device_register(&ti81xx_rtc_device);

I suspect you register the I2C RTC after the internal RTC, so I2C RTC goes to /dev/rtc1. Check if you map/register the I2C RTC (with platform_device_register()) first, it should go to /dev/rtc0

Regards,
Pavel

0 German Baranov over 8 years ago in reply to Pavel Botev

Intellectual 660 points

Hello!
First of all, thank you very much for your answers and sorry for the pause in conversation - I'm trying to digest information about RTC.
Definitely there is a queue somewhere, and omap_rtc goes first in it.
At the moment, this process seems to me more complicated than just platform_driver_register position in devices.c
i2c rtc is an i2c bus device and is instantiated by i2c driver (finally this event happens in MACHINE_START macro
in /arch/arm/mach-omap2/board_xxx.c) and judging by console messages happens first.
Then system rtc driver (/drivers/rtc) registers rtc devices ( function rtc_device_register in file class.c)
In this function number is assigned to rtc device, but choice of first and second device is not clear to me yet.
Regards
German

0 Pavel Botev over 8 years ago in reply to German Baranov

TI__Guru**** 170625 points

German,

Take a look also in the root filesystem etc/udev/rules.d/local.rules

See also the below pointers:

e2e.ti.com/.../440891
unix.stackexchange.com/.../how-can-the-link-target-of-dev-rtc-be-changed
developer.ridgerun.com/.../How_to_use_RTC_Real_Time_Clock_hardware

Regards,
Pavel

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rtc0, rtc1 assignment in Linux