Fixing the NTP Time Synchronization with Fonz funPlug 0.5 for CH3SNAS, CH3MNAS, DNS-323 and many more

The CH3SNAS has two internal clocks:

• a real-time hardware clock, which is similar to the chip in a wristwatch. It is powered by a battery inside the CH3SNAS and thus never stops.
• a software clock, which runs only when the NAS is turned on.

Unfortunately, the software clock drifts from the hardware clock and after a few hours the drift get noticeable (e.g., 16s/hour = 4444 parts per million) and the NAS will show incorrect times for e.g. file modifications. But thanks to NTP (the Network Time Protocol) the clock can be synchronized to one of the atomic clocks on the Internet. The resulting absolute error will be only a fraction of a second (e.g. 10 ms; because of packet delays across the Internet) and the drift will essentially become zero.

Note that this tutorial requires an installed Fonz fun_plug!

Background Information

The time in the Linux Kernel is a standardized value. One day equals 10000 “ticks”, so one tick = 8.64 s. Most of the CH3SNAS drift about 16s/hour, wich equals a drift of 384 seconds or 44.444 ticks/day. This value has to be subtracted from the 10000 Ticks of the Kernel and has to be set as the new number of ticks per day. In our case this 10000-44.444 = ~ 9956 Ticks. As you can see, this value is only an estimation because the drift is an estimation. As it will take a lot of time to get the exact value for the ticks, you can simply estimate them and synchronize periodically with a timeserver to reduce the clock drift.

As you can see below, there are two choices for the synchronization. Regular synchronization via Cron should be chosen over using the NTP-Daemon as the latter seems to cause the following two lines in dmesg reappearing over and over again until the device gets restarted:

kernel: TWSI: mvTwsiStartBitSet ERROR - Start Clear bit TimeOut .
kernel: TWSI: mvTwsiStopBitSet ERROR - Stop bit TimeOut .

The Procedure

Time-Synchronization via Cron

Simply add the following lines to /ffp/etc/fun_plug.local, e.g. with nano:

# This removes firmware cronjobs that interfere with ntpd.
crontab -l | grep -vw '/usr/sbin/daylight' | grep -vw '/usr/sbin/rtc' | crontab -
#Now start the ntp every hour
echo "1 * * * * /usr/sbin/sntp -r -P no de.pool.ntp.org" >> /var/spool/cron/crontabs/root
# force a cronjob update
echo "root" >> /var/spool/cron/crontabs/cron.update

Reboot the device.

Sidemark: If the NTP-Service has been deactivated before the restart.

NTP-Daemon

As described above, this method seems to cause the TWSI-problems and is here only for historical reasons. Probably due to the concurrent access to this Two-Wire-Serial-Interface by the ntp-daemon and the fancontrol.

Activating the Service

Mark the service ntpd as excutable:

chmod +x /ffp/start/ntpd.sh

Configuration of the Service

Copy the Example-Configuration from /ffp/etc/examples to /ffp/etc/:

cp /ffp/etc/examples/fun_plug.local /ffp/etc/fun_plug.local
cp /ffp/etc/examples/ntp.conf /ffp/etc/ntp.conf

Edit the /ffp/etc/ntp.conf to change the time servers to servers which are geographically close. You can search for them here.
Quick possibility: Change them to general ones:

server 0.pool.ntp.org iburst
server 1.pool.ntp.org iburst
server 2.pool.ntp.org iburst
server 3.pool.ntp.org iburst

With this configuration both clocks get adjusted to the German timezone. If you want to change the timezone, you have to edit the /ffp/etc/fun_plug.local.
The string for Germany is (also change the timeserver, as this one is for Germany):

timezone="CET-1CEST-2,M3.5.0/02:00:00,M10.5.0/03:00:00"
timeserv=de.pool.ntp.org

Change it according to your Timezone. You can find possible ones in the appendix

Start the Service

You can now start the service manually or you can perform a reboot (it will be started during the bootup):

/ffp/start/ntpd.sh start

Finetuning

After a few hours you can find a file called /ffp/etc/npd.drift on you CH3SNAS. If the Value is +500 or -500, you have to adjust the number of ticks in the file /ffp/etc/fun_plug.local. fonz has set this to ”tick=9965”, which may be right for your device. If not, try reducing or incrementing this value to reduce the drift.

Appendix: Example Timezone Strings