Hello, Nikolaus, В Пнд, 30/01/2012 в 21:13 +0100, Dr. H. Nikolaus Schaller пишет: > > 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...
First of all, really nice to see that open phone reached release state. As i were always wondering about SD reading issues in GTA02, which rises voltage in driver with reduced clock at beginning, and is not working at 25MHz at all. I wonder can it be related to that capacitor? Are GTA04 users going to experience same speed issues with SD like in GTA02? Gennady _______________________________________________ Openmoko community mailing list [email protected] http://lists.openmoko.org/mailman/listinfo/community
