[Gta04-owner] GTA04A4 starts shipping tomorrow

PaulK paulk at paulk.fr
Sat Feb 4 18:26:42 CET 2012



"Dr. H. Nikolaus Schaller" <hns at goldelico.com> a écrit :

>Dear all,
>you may have wondered a lot why it was so quiet about the GTA04A4
>boards in the last weeks. And nobody did report about unboxing
>experiences, because nobody did receive a new GTA04.
>
>The reasons where manifold. It started with soldering issues where they
>had to make a new stencil. This improved soldering quality a little but it
>was still not perfect. So we got much less good boards out of the soldering
>machine than planned and chips had to be replaced...
>
>Then, we did test the boards completely. It turned out that they still had
>some minor issues. The most maddening bug was that there was an error
>in the GND flooding of the backup battery. Therefore it was shorted on the
>PCB and could not work.
>
>After fixing this and testing more, we found out that the new circuit that
>is intended to allow the CPU to control the power of the UMTS modem
>through a GPIO did not work as intended. Rather than shutting completely
>down it did put the module into reset state. This would have been ok, if
>reset would be the same as power down. But the module draws 16 mA
>in this state. Even more than a not powered down modem in the GTA04A3
>boards which draws 3-10 mA and can wake up the CPU...
>
>So we finally found a way to solder a NPN transistor with built-in bias
>resistor to the position of some test pads and other resistors to make
>it work. This made us again bring the boards to the factory and
>have them do some hand-rework. And wait some days...
>
>Then, last week, we got the first boards that did pass all automatic
>tests and could power down completely (to some 300 uA for RTC).
>
>Happily we did install them into the first GTA02 cases to build the
>"OpenPhoenux" (GTA04 Complete) units. They worked fine, until we
>wanted to operate the GPS. It did not work well with internal antenna,
>but really excellently with an external antenna (up to 11 of 12 satellites
>used for navigation).
>
>We found out that the U.FL antenna socket was mounted in the
>wrong orientation (180 degrees rotated). This shorts the power
>supply of the internal Antenna (which has an amplifier built in).
>
>So, boards did go to rework again. Now, GPS with internal antenna
>was a little better, but still very weak.
>
>After 3 days of intensive research (incl. this weekend) we did find the root
>cause: it is the same as it was for the GTA02A5 board [1]. The SD card
>clock. It is 25 MHz and 25 * 63 = 1575 MHz, i.e. the GPS frequency.
>
>This means that the GTA04 creates some noise which is neglectable
>in more than 5cm distance with an external antenna, but not for the
>active GPS antenna built into the case. And some boards and
>antennas are a little better and others are a little worse so that it
>results in a basically working, but very unreilable receiver.
>
>The main problem was to find a measurement setup that gave
>reproducible results so that we could not only compare devices, swap
>antennas and try different shielding scenarios, but also check the
>effectiveness of measures against the problem.
>
>Like with the GTA02 there is a hardware and a software fix. The SW fix
>was to re-enable a feature in the 2.6.32 kernel that we had disabled due
>to problems with the SDIO driver. It appears that it is not at all necessary
>to change anything in the 3.2 kernel. So please forget immediately that
>there is a SW fix :) Because it fixes our unawareness and not a problem...
>
>The real hardware fix is adding a small capacitor like for the GTA02A5.
>
>You may wonder why we did not find it earlier. One aspect is testing time.
>The more testing you do the more issues you find. But we simply did
>not have enough GTA04A3 boards to do these tests...
>
>This time it was better and we could set up, test and compare e.g.
>5 GTA04A4 boards in parallel. And swap antennas between units etc.
>This simply was not possible before.
>
>So after having applied this last hand-rework, we have the first boards
>and devices that are in our opinion good enough to really be shipped
>and make you happy! More boards will become available next week.
>
>And we have some boards to show during FOSDEM next weekend.
>So please come and have a look!
>
>Finally, it is still time to subscribe to the Group Tour (which will get
>another board redesign where all these things are done right from
>the beginning - but otherwise they are equivalent).
>
>Nikolaus
>
>[1]: http://wiki.openmoko.org/wiki/GPS_Problems
>
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