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sd card space left — Parallax Forums

sd card space left

OwenOwen Posts: 100
edited 2007-07-11 17:25 in Propeller 1
Is there a way to check the amount of space left on an sd card using Tom Rokicki's sd card code? how hard would this be to add? any ideas on how to go about this?

Owen

Comments

  • mirrormirror Posts: 322
    edited 2007-07-11 06:44
    I've added the following function to my stuff.
    PUB GetTotalSectors
  return totclusters << clustershift

    Probably not quite what you're looking for, but it might start by·pointing you in a direction.

    ·
  • rokickirokicki Posts: 1,000
    edited 2007-07-11 06:55
    It's not *terribly* difficult; you just need to scan the FAT table and count the number of "empty" chunks.

    I'm curious what you need it for. I'd be happy to write it and add it in.

    -tom
  • BaggersBaggers Posts: 3,019
    edited 2007-07-11 08:28
    rokicki, on a side note, any chance of a seek routine?
  • OwenOwen Posts: 100
    edited 2007-07-11 14:43
    I'm sending large amounts of data(XYZ coordinates to translate a camera over time) in from a host computer to the sd card on the propeller. I just need the host to know how many coordinates it can store before before the card if full. If your interested in adding a way to determine space left on the card to the sd driver that would be great!

    thanks for the help

    Owen
  • rokickirokicki Posts: 1,000
    edited 2007-07-11 15:56
    Okay. If I write it in Spin, to calculate free space will probably take on the order of a second.
    (I need to read in 131KB of FAT table and then individually examine about 65,000 words for
    specific values.) It's possible it will take significantly longer than a second; I haven't tried it
    yet. If it takes that long, is it still useful for you?

    On seek, sure, anything's possible. (Indeed, there's already a certain amount of seek code
    in place for the "append" mode.) I just need to be motivated. Also, everything I add to
    fsrw makes fsrw larger, and there still isn't an officially blessed way to do conditional
    compilation or dead code elimination. I may add some stuff like this this month.
  • OwenOwen Posts: 100
    edited 2007-07-11 16:33
    Yes I think it would still be very useful. The time it takes to determine space available isn't a big deal to what I'm doing, I really need to check it just once before dumping data into it. Seems that it will be a great addition to the already great sdcard object.
    thanks again

    Owen
  • rokickirokicki Posts: 1,000
    edited 2007-07-11 17:25
    My pleasure; should be very easy to add and test. I'll do it by this weekend most likely (the free space, not the seek).

    On the seek, do you need full seek semantics and r+ and w+ opening, or would just seeking-on-read or seeking-on-write
    do? What do you need seek for anyway (motivate me please)? Because seeks need to follow FAT chains and FAT chains
    don't fit in memory, it's *possible* that seeks can be quite slow (in particular, backward seeks need to scan from the
    front of the file all over again; on a large file and depending on how contiguous the file is this could take quite some time.)

    In a degenerate case (random FAT chains), even recoding things in assembly won't speed it up. The worst case is probably
    a backwards one-byte seek requiring 65,000 block reads (so 65 seconds, roughly) if the FAT chain is completely random.

    In real life the FAT chain will *probably* be contiguous, so things won't typically be this bad, but seeking on large files can
    take a while just because of the number of FAT entries that need to be examined in Spin.
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