has anyone got a linux kernel driver for mcp79410 rtc  -solved

creates the /dev/rtc0 device, and after a bit of prodding*, hwclock -w set the time on the rtc, and hwclock -s can now be used in /etc/rc.d/rc.local to set the system time from the rtc (and hwclock -r shows the rtc time and date)

*(to explain the prodding. initially after running above, I got ioctl errors when running hwclock. I then did

There's a bit in one of the registers needs setting to start the oscillator running, probably you'll have problems until the oscilaltor is running and the initial date/time is set. Theoretically you only need to do it once - or at least until you loose both main power and battery.

I'd imagine you could do it properly with i2cset having read the datasheet to find the right bit.

i've looked at the datasheet, and according to it, one should set the highest bit (bit7 if you start at bit0) to 1 to start the oscillator. because the ports are not symetrical (you read from control address 0x6f for the rtc registers, but write to 0x6e) you have to do things a little more manually. -update: following tests, it would appear that dispite what the datasheet says, you can only write using the same control address as the read address.

get byte from location 0 and i2c0 location 0x6f.

HEXVAL=`i2cdump -f -r 0-0 -y 0 0x6f b|tail -n1|awk '{printf("%#x\n",$2)}'`  

then or the value with 0x80 to turn on the oscillator bit

NEWHEX=`echo $HEXVAL|awk '{printf("%#x\n", or($1,0x80)) }'`

then write the new value back to the rtc . note: the rtc driver must be unloaded to sucessfully run i2cset on the rtc. even with -f it will not write unless you   rmmod rtc_ds1307

i2cset -f -y 0 0x6f 0 $NEWHEX

you can now reload the driver  modprobe i2c:mcp7941x

and if it hasn't been configured, echo mcp7941x 0x6f > /sys/class/i2c-dev/i2c-0/device/new_device

below is a sample script I wrote which does the turning on/off of the oscillator on the mcp79410 rtc usual disclaimer. it works for me. try it at your own peril. i release it public domain. it probably works on all sorts of distributions, but is only tested on slackware 14.0 with custom 3.6.1 kernel with rtc support compiled in and rtc-ds1307 compiled as a module. (and it requires i2c-tools to be installed, and i2c-dev module to be loaded.)

#!/bin/sh
#this must be run as root.
if [ "`id -u`" != 0 ]; then
  echo "this script must be run with root priviledges to access the hardware"
  exit 1
fi
#and i2c-dev needs to be installed
if [ ! -e /usr/sbin/i2cdetect ]; then
  echo "you must install i2c-tools package to be able to configure"
  echo "devices on the i2c buses."
  if [ -e /etc/slackware-version ]; then
    echo "you can build a package using the slackbuild from www.slackbuilds.org"
    echo "or by using sbopkg, or your method of choice"
  fi
  exit 1
fi
FORCEFLAG=""
if [ -e /dev/rtc0 ]; then
  echo "warning. the kernel has already got the rtc driver loaded"
  echo "you will need to unload it with   rmmod rtc_ds1307"
  echo "then reload it with               modprobe i2c:mcp7941x"
  echo "when you have set the oscillator."
  exit 1
fi
#make sure we have a mcp7941x rtc present on the i2c bus
RTC_READ_PORT="0x6f"
#RTC_WRITE_PORT="0x6e"
#write port doesn't seem to work but you can write to the read port!
I2CBUS=""
if [ -e /dev/i2c-0 ]; then
  #we have an i2c-0 bus so lets see if the rtc is here
  ISRTC_HERE=`i2cdetect -y 0|grep "60:"|cut -c50|awk '($1!="--") {print "YES"}'`
  if [ "$ISRTC_HERE" = "YES" ]; then
    I2CBUS=0
  fi
fi
if [ "$I2CBUS" = "" ]&&[ -e /dev/i2c-1 ]; then
  #clock wasn't on i2c-0 but we have an i2c-1 so lets check it
  ISRTC_HERE=`i2cdetect -y 1|grep "60:"|cut -c50|awk '($1!="--") {print "YES"}'`
  if [ "$ISRTC_HERE" = "YES" ]; then
    I2CBUS=1
  fi
fi
if [ "$I2CBUS" = "" ]; then
  echo "no mcp7941x rtc detected."
  exit 1
fi
echo i2cbus is $I2CBUS
#now get the current seconds (bcd with oscillator control flag in top bit)
#and switch the oscillator bit on by or'ing the output with 0x80
HEXBYTE=`i2cdump $FORCEFLAG -r 0-0 -y $I2CBUS $RTC_READ_PORT b |tail -n1|awk '{print "0x" $2 }'`
echo "hexbyte is $HEXBYTE which is $(($HEXBYTE))"

if [ `echo $(($HEXBYTE))` -lt 128 ]; then
  echo "oscillator is not running"
  NEWHEXBYTE=`echo $(($HEXBYTE))|awk '{oscon=or($1, 128);printf("%#x\n", oscon) }'`
  echo "new hexbyte is $NEWHEXBYTE"
  #now lets write the new value to the writable address for the rtc
  #the writable address is the same as the read one, but with the 0 bit cleared
  i2cset $FORCEFAG -y $I2CBUS $RTC_READ_PORT 0 $NEWHEXBYTE b
  echo "started the oscillator"
else
  echo "oscillator is already running"
  echo "do you want to stop the oscillator y/n:"
  read i
  if [ "$i" = "y" ]||[ "$i" = "Y" ]; then
    #remove top bit from byte
    NEWHEXBYTE=`echo $((HEXBYTE))|awk '{oscoff=and($1,127);printf("%#x\n",oscoff) }'`
    echo "new hexbyte is $NEWHEXBYTE"
    i2cset $FORCEFLAG -y $I2CBUS $RTC_READ_PORT 0 $NEWHEXBYTE b
    echo "stopped the oscillator"
  fi
fi

have fun :-)