Laszlo KREKACS wrote: > I use the distribution on NAND as an SD card reader.
Hmm, I think we have to distinguish between things you can do and things that actually make sense here ;-) Once you've started to fill the niches, it's always unpleasant to change. That's one reason why it's difficult to make architectural changes like switching from a NAND-centric approach to an SD-centric approach once a system has been deployed. But in a new system, features should be open to evaluation, and if one can accomplish the same tasks in a simpler and cheaper way, that only helps to make the product stronger. The problem with NAND is that it's no end of hassle. You need a complex boot loader to use if fully, you need an in-system recovery architecture, it needs special partitioning, you have to deal with unusual error patterns (factory-bad blocks and wear), etc. An SD-centric design does away with all this and brings the whole architecture much closer to what you find in a PC. I.e., the analogy SD == disk holds true for most purposes. So you don't need to learn a whole new set of methods and tools to perform routine tasks but you can just handle them exactly like you'd handle a PC. For your SD reader scenario, there are actually two solutions: - you can just have a small system on the SD card that boots into an initramfs. Once the system has been loaded, you can remove the card and insert another one. - USB microSD readers sell for < USD 3 and make a nice addition to the travel accessories bag for each laptop that doesn't have an SD slot. > and I write the new distro to the uSD card. It is impossible to do it > on the same > SD card, from where the OS is running. You cant simply repartition > the uSD card. Why not ? Just get a big enough card and partition it before using it the first time. The total cost of a card with several GB is likely to be much lower than that of those few hundred MB of NAND. (It's not only the cost of the chip per se but also how this constrains the choice of packages, complicates sourcing, production, and all that.) > Furthermore, I used recently TangoGPS, and it broke the filesystem where the > maps were located. It broked every time when the phone runned out of battery. Hmm, frequent data loss looks like a problem that needs solving anyway, whether there is NAND or not. Does your user space attempt a shutdown when it notices an imminent low battery condition ? > I see only one alternativ: two uSD card slot. That's actually an attractive feature anyway. Basically one acting like a hard disk and the other one like a USB stick. Thinking of it, you can actually do this already if you have a suitable cable, since the USB port can be switched to host mode. > I think I made a fair point, so please save an emergency path. The design of a typical Qi system (whether NAND-free or not) should include a partition with an small user space for the boot menu and just this sort of recovery environment. There's no disagreement that you need this sort of functionality, there are just better ways to do it than to use NAND :-) Ah, and to recover from a truly catastrophic SD failure, there's always the option of carrying a backup card. There are also failure modes where you're much better off with SD than with NAND. E.g., if your device fails completely and needs to be replaced, you can't backup your NAND if your device is broken, while you can usually still remove your SD card and access it with another computer. - Werner _______________________________________________ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community