On Thu, Jun 14, 2012 at 11:34 AM, Christophe Aeschlimann <c.aeschlimann@xxxxxxxxxxxx> wrote: > Hi, > > Le 13.06.2012 23:31, Ran Shalit a écrit : > >> Hello, >> >> I hope you can help main understand issue of file system for embedded linux. >> I read free-electrons "Embedded Linux system development training" and >> some of the files recommended there such as cramfs, are aceesing the >> flash during execution of apllications. As far as I understand >> accessing the flash after initilization is not good in embedded >> system. > > > Define not good... some applications requires write accesses to the > flash. (how would you program music in your MP3 player ? Where do you > store crash dumps so they are persistent across reboot ? Where do you > store your user configurable options, etc.) > > There are different kinds of flash memory but each have a limited number > of program/erase cycle so you have to use them sparingly. (e.g. make > sure the write accesses are distributed across the chip that's called > "wear levelling", detect when bits have toggled and correct the error > using some extra redundancy stored in the out-of-band area of each block > (e.g. ECC). If the error cannot be repaired mark the block as unusable. > > When you access the bare memory chips then these issues are solved in > the different layers of MTD [1] and the specific flash file system [2] : > JFFS2, UBIFS, etc. > > If you don't access the bare memory chips e.g. you use eMMC or an SSD > these problems are left to a dedicated controller/firmware. > > [1] http://www.linux-mtd.infradead.org/index.html > [2] http://elinux.org/File_Systems > > Best regards, > > -- > Christophe Aeschlimann > Hi Christophe, Thanks for the reply. I have no need to write to flash during the main application execution: I will program the configuration and executable before start of execution, and after initialization there is no need to write again to flash. What I still do not understand is why cramfs, ubifs are recommended for embedded if they access the flash. Is accessing the flash not a problem in embedded linux ? What does it mean using mlockall with cramfs ? Regards, Ran -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
