From OpenCircuits
Jump to: navigation, search

Tideclock boardassy 01.jpg

Here are the two PCBs comprising the clock. I haven't finished the wooden cabinet they will go into. Stay tuned...



Tideclock is an electromechanical clock that displays local tides in bargraph form. The 'bars' are currently implemented as 12 moving pointers on lead-screws approximately 30cm long, but there are many other neat ways one can display a 'bar'. How about columns of water? or a string that is supported at a dozen places?

Being software-controlled, many parameters that are easily altered, such as:

  • interval between the 'bars' (presently 1 hour, thus showing the upcoming tides for 12 hours)
  • location for which the tides are calculated
  • display scaling, or units

One can even display currents instead of tide heights if preferred.

TideClock uses a Linuxstamp by Paul Thomas (see its page here in OpenCircuits) for the processing.

Tide calculations are performed by xtide [[1]] compiled to run on the Linuxstamp.

Motion control and power supply is performed by a custom PCB. The design details are below.


The Software works. A prototype PCB has been assembled and 90% tested. The major remaining tasks are assembling the lead screws and putting the whole thing in a nice wooden cabinet.


  • 12 individually-controlled 'bars' for displaying the tide height 12 or 24 hours in the future
  • Low power (60 mW between updates; 1.2W when updating the graph)
  • configurable Update interval (how often graph is refreshed)
  • configurable Scale (meters, feet, fathoms, etc)
  • Displays Tide Height or Current Speed


All files for this project are licensed under the GNU GPL V2


The prototypes (4 are in various stages of construction) have cost about $500 each for materials. Labour not included...

Hardware files

Warning!!! Use this design at your own risk.

Download the hardware files here. This .ZIP file contains two subfolders: a Design Files folder with the Altium-format schematic and PCB layout files; and a Manufacturing Files folder with the Gerbers and PDFs of the Schematics and Assembly drawings.

During building of the first 4 TideClocks, I made a few changes and am calling it revision B. The changes are:

  • decreased diameter of holes in pads for mounting Linuxstamp I
  • placed Max input voltage on silkscreen near solar input pads
  • included PCB and Assy part numbers
  • corrected polarity of supercap on silkscreen
  • changed C207 2u2 to 1uF for commonality of parts
  • included 3D model of LinuxStamp I on 3D model of PCB.

The hardware files for revision B are here.


Energy is stored by an ~1100 mA-Hr Li-ion cell, which is sufficient for about 30 hours of use when disconnected from external power sources. It is recharged by either 5V from a USB-charger wall-wart, or a solar panel. Average power consumption is approximately 150 mW, so it shouldn't need too large of a panel.

The internal real-time clock (which is how the software knows what time it is, for the calculations) is powered by a 0.47F supercapacitor that charges from the the Li-ion cell. The TideClock should retain its internal time for at least two weeks after discharge of the main battery.

Console and Debug port

A USB connector provides a serial port for console access to the Linux OS. This is used for updating or changing the software, changing the time, or changing other parameters.

nfs & tftp

Cross Compiler



I left u-boot as-is on the Linuxstamp.


I configured Busybox pretty much as described for the Linuxstamp.

Building the Linux Kernel

Download kernel 2.6.33 from kernel.org. Get patch for AT91 from http://maxim.org.za/at91_26.html. Uncompress and apply patch:

cd linux-
patch -p1 < ../2.6.33-at91.patch 

We'll need to have mkimage in the path to create the uImage file, and we'll need the cross-compiler in the path:

export PATH=${PATH}:~/dev/uboot/tools:
export PATH=~/x-tools/arm-unknown-linux-gnueabi/bin:${PATH}
export CROSS_COMPILE=arm-unknown-linux-gnueabi-

Configure the kernel for compiling with the desired options:

make ARCH=arm ecbat91_defconfig 
make ARCH=arm menuconfig

In the kernel config menu, turn on/off these features as indicated. Some are optional, some you must do for it to work:

  • turn on Kernel Features->"Use the ARM EABI to compile the kernel" (MUST)
  • turn off "Kernel .config support"
  • turn off Bus Support->"PCCard"
  • turn off Kernel Features->"Allow old ABI Binaries to run with this kernel"
  • turn off Networking Support->Wireless->"cfg80211 - wirelss configuration API"
  • turn off Network Device Support->"Wireless LAN"
  • turn off Network Device Support->"PPP support"
  • turn on "I2C Core Debugging messages"
  • turn on Device Drivers -> Real Time Clock->"Intersil ISL1208" (MUST if you want to use the external RTC)
  • turn on Device Drivers -> CONFIG_RTC_HCTOSYS (MUST if you want the kernel to set system time from the RTC)
  • set Device Drivers -> Real Time Clock-> RTC_HCTOSYS_DEVICE='rtc1' (MUST indicate which RTC to pull the time from)
  • turn on RAMDISK support, so we can put kernel+rfs into flash and run the whole thing out of RAM. During booting the kernel+flash image is uncompressed into RAM and the rfs image mounted as /
    • in “Main menu”->“Device Drivers”->“Block devices” make sure “RAM disk support” is selected.
    • for the “Default RAM disk size” enter 14000 (this seems OK, in first tests we seemed to need a bit over 7 MB for the rfs.)
    • in “Main menu”->“General setup.” select “Initial RAM filesystem and RAM disk (initramfs/initrd) support”
      • enter the location of the RFS cpio archive, or RFS path (see below in RFS, read Help section if needed, or check linuxstamp page on OpenCircuits).

Build the kernel; in kernel directory ~/dev/kernel/linux-

make ARCH=arm CROSS_COMPILE=arm-unknown-linux-gnueabi- uImage
  Image arch/arm/boot/uImage is ready

If you entered the location of the RFS cpio archive in the make menuconfig, this uImage will include the RFS, else it will be just the kernel itself and you will need to provide the RFS via NFS or on SD card.

Load the kernel using Linuxstamp's bootloader and minicom's xmodem send option.

Root Filesystem (RFS)

See http://www.opencircuits.com/Linuxstamp and http://processors.wiki.ti.com/index.php/Creating_a_Root_File_System_for_Linux_on_OMAP35x

General steps:

  • Made staging dir
  • Ran busybox's make install to this staging dir
  • Made link in RFS root directory to busybox so kernel launches it
ln -s bin/busybox init	
  • Created the dev, dev/pts, etc, etc/init.d, lib, mnt, opt, proc, root, sys, tmp, var, and var/log directories.
  • Created the device node for the initial console:
sudo mknod dev/console c 5 1 
  • Created file etc/fstab with following contents:
proc            /proc           proc    defaults        0 0
none            /dev/pts        devpts  mode=0622       0 0
  • Created files group, hosts, and passwd in the /etc directory for logging in.
[root@localhost etc]# vi group

[root@localhost etc]# vi passwd

[root@localhost etc]# vi hosts       localhost
  • init reads the etc/inittab file to determine what to do at start up, shutdown, or when a user logs in. Created inittab (see sample in refs)
  • init runs /etc/init.d/rcS to setup the system. Created rcS (see sample in refs) and made executable by all.
  • created etc/mdev.conf
[root@localhost etc]# vi mdev.conf
audio       0:5 0666
console     0:5 0600
control.*   0:0 0660 @/bin/mv /dev/$MDEV /dev/snd/
dsp         0:5 0666
event.*     0:0 0600 @/bin/mv /dev/$MDEV /dev/input/
fb          0:5 0666
nfs         0:5 0770
null        0:0 0777
pcm.*       0:0 0660 @/bin/mv /dev/$MDEV /dev/snd/
rtc         0:0 0666
tty         0:5 0660
tty0*       0:5 0660
tty1*       0:5 0660
tty2*       0:5 0660
tty3*       0:5 0660
tty4*       0:5 0660
tty5*       0:5 0660
tty6*       0:5 0660
ttyS*       0:5 0640
urandom     0:0 0444
zero        0:0 0666
  • Added in libraries
    • Goto the RFS staging area and copy the cross-compiler's libraries into the staging area. Only the *.so libraries are needed. The *.a are used for statically linked programs. Use cp -P to preserve symbolic links, else the RFS gets bloated with actual copies of the libraries. Strip out debug info and unneeded symbols to make the libraries smaller.
cd ~/dev/kernel/rfs
sudo cp -rP ~/x-tools/arm-unknown-linux-gnueabi/arm-unknown-linux-gnueabi/sys-root ./
arm-unknown-linux-gnueabi-strip --strip-unneeded *
  • Finally, after you have set up all the libraries you need, run ldconfig to remake /etc/ld.so.cache on the RFS. The cache tells the loader where to find the libraries. You can do this with: (I skipped this step - didn't seem to be a problem (nothing needed the libraries?)
ldconfig -r /mnt
  • Make root owner of entire RFS
sudo chown -R root:root ~/dev/kernel/rfs

Including RFS in Kernel Image

See http://www.kernel.org/doc/Documentation/filesystems/ramfs-rootfs-initramfs.txt and also Linuxstamp page on OpenCircuits

The linux kernel source will have the needed scripts and utilities.

.../linux- /path_to_fs_root/ > cpio_list 

Make and invoke gen_init_cpio (in .../linux-

make gen_init_cpio 
../linux- cpio_list > initramfs.cpio 

Gzip the CPIO archive

gzip initramfs.cpio 

Copy initramfs.cpio.gz to usr/initramfs_data.cpio.gz, and run the normal kernel make. You will notice that uImage is much larger (size = kernel + fs).

Use Darrell's Bootloader on the Linuxstamp to upload the new kernel+rfs to dataflash. The Linuxstamp should now boot without an SD card and without an NFS server. The u-Boot kernel arguments can still include an nfs server rfs - they will be ignored.

I2C and RTC

The TideClock includes a Real Time Clock (RTC) (Intersil ISL1208) to keep time when the rest of the device is off. The kernel reads the RTC during booting to update the system time, which allows the tidal predictions to be correct for the current time. The RTC is powered by a supercap for several weeks of timekeeping when no other power is available.

Since the Linuxstamp CPU includes its own CPU. it would have been possible to rewire that board to provide a separate backup supply to its crystal but I thought it easier to leave the Linuxstamp unmodified and just provide a separate RTC. It turned out that using the Linuxstamp RTC was no more difficult that the way I chose, so for cost savings one could dispense with the separate RTC.

The ISL1208 communicates via I2C so I had to get that feature operating. As a start, read http://openhardware.wordpress.com/2008/10/13/i2c-fun-with-the-at91rm9200/

I tried

patch -i addRTC.patch -o board-ecbat91.c

but it failed to patch (not right version?) so I made the modifications by hand. A patch file for my mods will be posted shortly...

I also patched the at91rm9200_devices.c file to move the SCK pin from PA26 to PA24, and to slow down the I2C clock from ~167kHz to ~67kHz. A patch file for my mods will be posted shortly...

Remember to also edit the kernel's .config (using make ARCH=arm menuconfig as described in the Kernel section above) to enable the RTC portions of the kernel. Note that rtc0 points to the Linuxstamp's CPU (AT91RM9100) internal RTC, while rtc1 points to the ISL1208.

When testing I2C functionality, you can cross-compile the I2C tools from http://www.lm-sensors.org/wiki/I2CTools and they will run on the Linuxstamp. With the ISL1208 attached to pins 24 (I2C_SCK) and 25 (I2C_SDA), it appears on I2C bus 0 at address 0x6f (0b1101111x) and you can read back the minutes by:

./i2cget 0 0x6f 0x01

When an ISL1208 is powered up for the first time or following total power loss (i.e. no backup battery), its time registers will not begin updating until at least one of time registers has been written to. To write to the registers the write-enable bit 4 of register 0x07 needs to be set to 1 first. e.g. To set the time to 23 minutes after the hour, do:

./i2cset 0 0x6f 0x07 0x10
./i2cset 0 0x6f 0x01 23

The I2C tools won't access the clock when a kernel that has control of rtc1 is running. Use the busybox hwclock ... function instead. On the command line, set the system time/date and then write the system time to the ISL1208 by:

date -s "2011-12-29 11:40"
busybox hwclock -w -f /dev/rtc1

Reading the RTC is similar:

busybox hwclock -f /dev/rtc1                                                
   rtc-isl1208 0-006f: read time OK                                                
   Thu Dec 29 11:25:34 2011  0.000000 seconds

TODO: the ISL1208 can be tuned (calibrated) to minimize inaccuracies.

See also the kernel's ./Documentation/rtc.txt, which includes a test program for messing with the RTC. The sysfs interface under /sys/class/rtc/rtcN provides read-only access to various rtc attributes. Google for more info.

Note that the CPU's internal RTC (rtc0) is *not* updated automatically from either the ISL1208 or the system clock. If you plan on using it and want it synced with the rtc1/system time, the toss the following into /etc/init.d/rcS.

busybox hwclock -w -f /dev/rtc0

Power-saving Suspend

I was able to get the CPU to suspend to RAM and cut its current consumption to about 12mA. Before suspending, the internal RTC (rtc0) was set to wake the CPU after a set elapsed time (e.g. 15 minutes). This is used to update the TideClock graph at intervals and sleep in between to cut power consumption.

Details to follow shortly.

GPIO / Hardware Pin I/O


I won't repeat the ones listed on the OpenCircuits pages for the Linuxstamp and Linuxstamp II 9260.

USB Info


You could try the <Discussion> button at the top of this page, or contact me at the address below:


For questions or comments please contact Bjarne (bjarneh /at/ shaw /dot/ ca)

other Related Projects

Personal tools