Dieter Spaar wrote: > Anyone remembers GSM related differences between GTA01 and GTA02 ?
I remember that the multiplexer required some attention, but I don't recall if that actually required differences between the GSM firmware versions for GTA01 and GTA02. One of the voices in my head says that they ought to be the same. Perhaps Tony or Harald can remember ? > You mentioned already that FLUID has to be used differently on GTA01, is > this something related to FLUID itself or the way how the UART connection > is handled in GTA01 ? The difference is how we reset the GSM modem. The story goes like this: In the beginning (pre-production GTA01), we had a transistor to pull the modem's TESTRSTZ line low. That transistor connected to a GPIO of the CPU. So the process of establishing communication with FLUID was to fire it up, and then to reset the modem through this line. As part of its reset process, the modem would look for FLUID, find it, ... and they lived happily ever after. Then we noticed that, when powering the system down (PMU going into STANDBY state), the CPU would "jerk" its GPIOs in the last moment. This sometimes (I don't remember if it happened all the time or only some of the time) caused the GSM modem to get reset, after which it would happily stay powered up. Since we couldn't find a quick fix for the CPU's last struggle, we removed the transistor and devised a new mechanism: when sending the [EMAIL PROTECTED] command to the modem, it would power down. That had already been implemented for other reasons. Activating the modem's PWON line, which is controlled by a transistor driven by another of the CPU's many GPIOs, would wake the modem up again. This "button" signal is operated by writing to the sysfs file /sys/.../*gsm*/power_on PWON acts basically like the power button you would find on many phones. So it does a full power-on reset of the modem. This of course means that the modem also goes through the phase that lets FLUID establish communication with it. So once again, order was restored. And this is the situation in all production GTA01 devices. In GTA02, we had learned from our past mistakes and left the troublesome transistor on TESTRSTZ off right from the beginning. So the [EMAIL PROTECTED] sequence was the standard reset mechanism. However, another change had happened since GTA01, and that's the addition of an electronic switch to cut power to the GSM subsystem. The GSM subsystem receives its power directly from the battery and does not go trough the PMU. Therefore, you could never be quite sure that it was really off, and not secretly drawing power or informing the Ministry of Love and Happiness of your whereabouts. Unfortunately, this switch ended up being controlled by the very same power_on file that also triggered the PWON signal. I don't remember the details, but this arrangement threw off the reset process such that FLUID would not establish communication with the modem. Since we didn't want to change this interface for what was a bit of a fringe use, we had to find a way to operate PWON without affecting the power switch. That's why there is the mysterious tweaking of GPIO line B7 in the GTA02 flashing procedure. Alas, the minions of evil had planned ahead and equipped the GSM modem with the ability to detect the presence of such a switch between itself and the battery. This manifested itself by the GSM modem not working properly if that switch was there. So we eventually removed that switch in some GTA02 models, and they may now in fact be virtually identical to GTA01 when it comes to resetting the modem. However, the slightly more arcane procedure involving meddling with GPIOs works also in GTA02 after the change. Thus we have the following situation: on all GTA01, the modem can be reset to communicate with FLUID by first shutting it down with [EMAIL PROTECTED], and then writing to power_on (I don't recall the correct value to write offhand). On all GTA02, the same is accomplished by shutting it down with [EMAIL PROTECTED] and then pulling PWON low (by setting GPB7 high). - Scheherazade ;-) _______________________________________________ devel mailing list [email protected] https://lists.openmoko.org/mailman/listinfo/devel
