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Firmware architecture for firmware update

Discussion in 'Embedded' started by alacky3, May 20, 2011.

  1. alacky3

    alacky3 Guest


    I am implementing a program to be updated via GPRS channel. The total siz
    of the firmware reaches about 256 kB which makes it somewhat costl
    upgrades. I considered the idea of dividing the firmware into independen
    parts that can be updated independently and upgrade only the changed parts
    but I don't know how to begin. Does anyone has had a similar problem? Ho
    do you have solved it?

    alacky3, May 20, 2011
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  2. alacky3

    Tim Wescott Guest

    Under windows you'd do this with dll's. Even though I use Linux, I
    can't remember the name of the same concept, but the file suffix is .so.
    At any rate, whether your OS supports it or not you'd need to have
    nice logical modules well separated by function (so that upgrading one
    thing doesn't break all the rest) and a means of dynamically linking the
    separate bits.


    Tim Wescott
    Wescott Design Services

    Do you need to implement control loops in software?
    "Applied Control Theory for Embedded Systems" was written for you.
    See details at http://www.wescottdesign.com/actfes/actfes.html
    Tim Wescott, May 20, 2011
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  3. alacky3

    Marc Jet Guest

    256KB on GPRS is not excessive. It will finish in less than 4 minutes
    worst case (2G single timeslot).

    If you really need faster updates or less bandwidth usage, you could
    inspire with RSYNC. It improves throughput for files of which a
    "similar" version is already present on the other side of the link.
    What definition of "similar" works best for your application, depends
    on the details of your project.

    You can even improve a lot over RSYNC, if you know exactly what's on
    the other side (by firmware version identifier). You could then
    implement a "patch processor" (interpreter with defined command set),
    and produce a patch instruction stream, which you then optimize,
    compress and transmit. On the other side of the link, it is
    decompressed and executed, and patches the existing firmware into the
    new version. Done right, this is the quickest/shortest possible way
    of transmitting the update (because it is a compression algorithm
    optimized to the specific application at hand).

    However, I suspect that standard compression algorithms on the binary
    firmware image and possibly a recommendation of using better wireless
    technology (EDGE or 3G) is quicker to deploy than either of these, and
    the user will not notice much of a difference anyway.
    Marc Jet, May 20, 2011
  4. alacky3

    D Yuniskis Guest

    Presumably, you don't have a "spare" 256KB in the device to
    cache the image(s) -- persistently -- until *all* of them
    can be downloaded?

    If you try to do this piecemeal, you have potentially several
    hazards to avoid -- all having to do with incomplete or partially
    complete images being available.

    First, you have to have AT LEAST enough "cache" (though *this* can be
    volatile) to store the largest "piece" that you will be downloading.
    This safeguards against the case wherein the image can't be downloaded
    intact in a single piece (i.e., you can't risk "updating *while*
    downloading" for fear that the image is corrupted or interrupted
    *during* the download -- you need the previous "working" image
    to be available for your device to continue functioning in the
    event that the image isn't downloaded completely/correctly).

    You also need to have some strict sense of configuration management
    that allows you (your device and/or the device serving up these
    images) to know what the device in question's *current* configuration
    is and which "pieces" can be applied to that configuration to yield
    "operational" (albeit possibly with other "known bugs") configurations.

    For example, if the user is at version A.0, possible upgrade
    paths may be A.0->A.1->A.3->A.7->B.0, or A.0->A.2->A.7->B.0
    depending on which "modules" are updated along the way. Note
    that the path taken will determine which functionality (and
    "bug-onality") the device retains *while* it transitions to the
    final state (recall that the process may take minutes, hours,
    weeks, months or YEARS! Since you are allowing it to be
    "interrupted" -- albeit at known points -- you have to consider
    the possibility of the device *staying* in one of those intermediate
    states indefinitely!)

    This also has to address the fact that the user may *not* have applied
    all of the upgrades that you require. I.e., you need to account for
    how to get that device to a state (*the* state?) that your current
    set of upgrades expects/requires.

    And, throughout it all, you have to make sure that the upgrade
    process itself continues to function flawlessly. (if you brick the
    user's device, he won't be happy!)

    The actual mechanics of creating an updatable framework are
    conceptually pretty simple: finely *define* modules that are
    *small* enough and "independant" enough that they can be replaced

    As I said above, the bigger problem is accurately tracking the device's
    current configuration and *knowing* what behavior you (and the user)
    can expect from the device in *all* of those possible states.
    (i.e., imagine a user who got to A.7 but never took the final step
    to B.0. That user calls you complaining that his device is exhibiting
    some "unusual behavior". You need to be able to recognize that the
    device is at A.7 and needs to progress to B.0 to be in a "supported"
    D Yuniskis, May 20, 2011
  5. alacky3

    Nobody Guest

    The formal term is "dynamic shared object" or "DSO", but most people seem
    to call them "shared libraries" or "dynamic libraries" (or occasionally
    even "DLLs", if they've been using Windows too long).
    Nobody, May 20, 2011
  6. alacky3

    linnix Guest

    It's either Dynamic Linking Loader (dll) or Dynamic Loading Linker
    (dll) for Shared Objects (so). However, there are quite a bit of run-
    time overheads using them. For firmware, it might be easier to just
    separate the library into "ROM" code and calls, traps or soft intr.
    into it.
    linnix, May 20, 2011
  7. alacky3

    Tim Wescott Guest

    Yes, anything that's dynamically linking is going to be slow -- I was
    trying to get some concepts and search terms to the guy as much as make
    specific recommendations.

    Certainly if size and speed were a concern, I'd want to do this with
    something more statically linked (although I can't see how to avoid jump
    tables or the equivalent). I can think of several ways to do this right
    off the bat, but in the end you're going to have to sacrifice some
    combination of speed, versatility, or design time.


    Tim Wescott
    Wescott Design Services

    Do you need to implement control loops in software?
    "Applied Control Theory for Embedded Systems" was written for you.
    See details at http://www.wescottdesign.com/actfes/actfes.html
    Tim Wescott, May 20, 2011
  8. alacky3

    John Speth Guest

    Under windows you'd do this with dll's. Even though I use Linux, I
    I think (not sure) the shared library approach is slow only the first time
    the library is demand loaded. After that, use of the library is the same as
    if it was statically linked. Isn't that the extent of the slowness of shard

    I'm not sure of the memory resource usage at load time. I'll bet it's
    temporary (extra memory released after loading happens).

    John Speth, May 20, 2011
  9. The 256kB is not much; looks like a monolitic application to me.
    Breaking it into the chunks would be difficult and inconvenient.

    The good way to deal with this problem is DIFF. I.e. a compressed format
    which uses the current application as a dictionary for the compression.
    Only the references to the current dictionary and the changes have to be

    Vladimir Vassilevsky
    DSP and Mixed Signal Design Consultant
    Vladimir Vassilevsky, May 20, 2011
  10. alacky3

    Nobody Guest

    The global offset table (GOT) and procedure linkage table (PLT) have to be
    generated each time a program is executed. The use of position-independent
    code means that relocations don't have to be performed within the actual
    code. The PLT can either be generated at startup or be generated lazily,
    i.e. each entry is generated the first time that the function is called.
    The GOT is always generated at startup.

    Linking against static libraries results in the use of fixed addresses.
    This reduces startup time, as no GOT/PLT entries are required, and
    increases execution speed slightly (a typical estimate is 4%) as a level
    of indirection is removed. The main performance downside is that, if
    multiple processes are running different programs which use the same
    library, each program will have its own copy of the library, which
    increases the demand for memory.
    Nobody, May 20, 2011
  11. alacky3

    larwe Guest

    I wish this was true. In real world conditions I can tell you from
    bitter personal experience that it is more like two hours
    "worst" [observed] case with an average more like 30-45 minutes.
    That's for a gzipped image that was originally 256K pre-compression,
    too. Tested in many many sites.
    larwe, May 21, 2011
  12. larwe skrev 2011-05-21 04:33:
    Normally, you pay per bit and not per minute,
    so is the time important?
    In Sweden, to download 256 kB would cost about $0.50.

    Ulf Samuelsson
    Ulf Samuelsson, May 21, 2011
  13. The thread starter was talking about a firmware image of 256 kByte
    total. I doubt he's using a full off-the-book System V shared object
    implementation. There's plenty of room for optimisation.

    For example, the GOT and PLT can be generated at the time of the
    firmware update. The shared object can be stored in fully-relocated
    form. It doesn't have to use position-independant code if we can patch
    the binary code. Essentially, this is what MS Windows does. It's called
    This is what happens when you load a Linux kernel module. Up to kernel
    2.4.x, a module is a standard .o file, which is statically linked
    against the running kernel (in 2.6 it's slightly different but the basic
    process, as far as I know, is the same).

    Stefan Reuther, May 21, 2011
  14. alacky3

    larwe Guest

    Sure, it is per-byte payment here in the USA also (except for lucky
    people like me who kept some old iPhone account SIMs active to be
    grandfathered into unlimited data ;) but the problem is downtime, and

    Downtime can be removed if you have enough space to store a redundant
    image, but the sequencing/scheduling issue is very important. Our
    equipment for instance may need for legal reasons to have a technician
    must be on site when the upgrade is rebooted to test the system and
    certify it operation. The ideal scenario would be for tech to arrive,
    push "upgrade", wait for the code to arrive (a few minutes is ok),
    then test the system and leave. Since the time is so unpredictable and
    always LONG, this workflow doesn't work.

    Also bear in mind we are deploying to hundreds of thousands, if not
    millions of units.
    larwe, May 21, 2011
  15. alacky3

    David Brown Guest

    Can you separate code and data? Maybe the 256K contains tables, images,
    fonts, or something that is relatively fixed, and can be separated.
    It's a lot easier to add a little indirection to the access of such
    tables than to have more general dynamically linked libraries.

    Can you patch the firmware, so that the user downloads a delta from one
    version to the next?
    David Brown, May 21, 2011
  16. A straightforward solution is to have two sections for each library.
    One section contains addresses of subroutines in the other section.
    The main program and the libraries are linked to the section with
    the addresses.
    The linking can be difficult, but I blame those linkers,
    because this is conceptually simple.

    Each pair of sections must be put in a fixed place.
    A pair of sections can be exchanged without affecting linking.
    The overhead is very small, an extra indirection.

    In assembler it is a snap, especially with macro's.
    In c it looks bad.
    An instrumented c-compiler could handle it transparently.

    The details are much dependant on the tools you have available.
    Groetjes Albert
    Albert van der Horst, Jun 1, 2011
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