[lm-sensors] RTC + DS1337
be.terawatt at laposte.net
Thu Jun 29 09:06:54 CEST 2006
I faced a problem with DS1337 RTC. I use a pxa255 cpu with 2.6.16
kernel. I tried to make a DS1339 chip (real time clock) working with
In my config, I selected I2C, DS1337/DS1339 driver, and ehanced RTC
support to have it working with /dev/rtc as expected by hwclock. That is
to say the following options:
The ioctl() to dev/rtc did not work. While investaigating on that issue,
I found 2 problems :
- the option "Enhanced Real Time Clock Support" (config RTC) does not
provide generic access to a RTC chip via /dev/rtc as I belevied. The
access to the chip in driver/char/rtc.c are made with CMOS_READ() and
CMOS_WRITE(), defined in Linux/include/asm-arm/mc146818rtc.h. It is a
combination of outb_p() and inb_p() : no chance to access my I2C chip
So I added ioct() support in /drivers/i2c/chips/ds1337.c.
- the driver (/drivers/i2c/chips/ds1337.c) has two problems (I'm not
sure it is bugs, but at least on my system it does not work).
First, ds1337_detect() reads some values in the chip registers that are
assumed to be wrong, but in my chip they do exist (I swear I have a
DS1339). I commented out these checks.
Then, the part that enables the RTC after first power up in
ds1337_init_client() fails to write a status bit in the chip, so we fall
into the same reset code (that writes zeros in the RTC regs) after each
I corrected this and that's OK for me.
I can post code if it is usefull for someone.
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