Ok, here is what an SD card has - it has a RAM buffer that is the size of a block, where a block is the smallest erasable chunk. That is what "Erase Pooling" is vaguely referring to. If you are going to write sectors in the same block, you should do that, send all the sectors in that block then issue the write command.
If you write individual sectors, the card will do an erase/rewrite for each sector on the entire block, and it will be very slow. As to who does this, it depends, but it is harder that it may sound, because now you have to track things based on the "geometry" of the card and know when to do the write. The code is much simpler if you just write each sector as it comes up. Most SBC cards just use an SPI to talk to the card. But that is all the card does for you. > Well it's up to the controller to do that perhaps. Given that most people > seem t use usb adapters for SD cards, the OS simply sees a USB storage > device and runs FAT or some other filesystem on it. Certainly no wear > leveling done in software. Perhaps the usb adapter does it. > > > -It take can take up to something like 40ms to write a single sector, as > an > > entire block must be erased and re-written.For a given card, it is indeed > > specified. Cards have different speeds, but that that is available from > the > > internal config data of the card and the mfg specs - which are published. > > The card indicated via status when it is done (of course only the driver > is > > going to see that) > > > > -As for "low level formatting", huh? Unlike a hard drive, a sector is a > > sector. While writing a stand alone driver, I scrambled the data plenty > of > > times, and reformatting with windows "format" never failed to work. You > > might be assuming it is like CF, which does emulate a hard drive. > > Certainly CF cards do have to do any wear leveling in the card since > they present IDE to the host system. > > > You should get the spec from the SD people for 1.1 and read (parts of) > it. I > > think your issues are with the the OS/Driver and the way you are doing > > things. Used correctly, SD cards will work fine. > > Unless you have many files open, it should complete quickly. > > Well there might be some really bad SD cards out there too. > > -- > Len Sorensen > _______________________________________________ > uClinux-dev mailing list > [email protected] > http://mailman.uclinux.org/mailman/listinfo/uclinux-dev > This message was resent by [email protected] > To unsubscribe see: > http://mailman.uclinux.org/mailman/options/uclinux-dev >
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