> Hi,
>
> Good afternoon. i have several issues that i am in
> doubt.
>
> 1. what is embedded system? what is the difference
> between a normal electronic system with a uC, with an
> embedded system?

    Here's a definition of embedded system:

    http://www.mitre.org/research/y2k/faq/embedded.html#1

> 2. i am used to programming pic16F84 and 68hc11. the
> procedure is like this. key in the assembly in an
> editor, them assemble them to hex file, then download
> them to the uC. that's it. the uC can be brought
> everywhere and still function the same.
>
> My question is, why people are telling me that i need
> a RTOS ( Real Time Operating System ) to develop an
> embedded system? They are telling me that drivers need
> to be written, so on and so forth. Why?
> What role does the RTOS play?

    What you have been programming all along
    is what's call the "foreground/background"
    or "superloop" system.

    That is, an application in an infinite loop
    calling different modules/functions to perform
    a desired operation in the "background"

    Occasionally it is "interrupt"ed to perform
    some critical task in the "foreground".
    These are your interrupt subroutines.

    This system works fine for most application.

    Biggest drawback is that modules/functions
    in the "superloop" does not get it's
    share of CPU time at a constant rate, or
    to put in RTOS-speak, it is in a
    non-deterministic manner.
    The rate that your function gets executed
    depends on the time taken by other
    modules/function calls in the loop.

    This becomes a problem when your "background"
    system or "superloop" gets increasingly
    complicated with more and more modules.
    When system that previously works fine,
    but no longer works when new code is
    added to the "superloop".

    How then can you ensure that a function
    IS executed, say every 10 millisecond.
    Task/function response time will be
    "non-deterministic" in your current
    system, because you have to go thru
    the all modules in the "superloop"
    before it gets to your function.

    Best example is a system where you
    enter a key, but sometimes, nothing
    happens until a certain time later.
    Sometime fast, sometime slow.

    This is one side-effect of
    non-deterministic system.

    You probably can use a timer interrupt
    to perform this task.

    But what if you have more and more functions
    that need to be executed every, say 5ms, 50ms,
    1s, 1 hour, 1 day etc.

    This is where a RTOS comes in.
    With an RTOS, every task/module/function
    is given a share of CPU time at a
    predetermined rate and prioritized
    according to a predetermined task
    priority.

    This ensures that the highest priority
    task gets executed as quick as possible
    by the CPU and thus improves and
    optimises overall system responsiveness.

    This means that a task that is just
    waiting for an event (such as keypress)
    can give up CPU time to other more
    important task, instead of hogging
    CPU time in a polling loop.

> i don't get it, cause i am still looking things at the
> binary level.

    You will, once you start working on
    bigger and more complex systems, when
    even assembly coding will no longer
    do.

    You'll most probably need to move on
    to higher-level language such as C.

> 3. Another issue is the driver issue. When someone
> told me that driver need to be written for certain
> embedded component, i start to go blank. how should i
> start?
> Another senior engineer told me that i have actually
> been writing drivers without knowing it. really?

    A driver is just a piece of code that
    you write to make certain piece of
    harware function.

    Say you have an external EEPROM, the
    code you write to interface with that
    EEPROM is the driver.

>
> Can anyone please enlighten me?
>
> thanks a lot
>

    Hope the explanation helps.

    If you want to learn about RTOS, a good
    book is "MicroC/OS-II, The Real-Time Kernel"
    by Jean Labrosse. www.micrium.com

    Highly recommended and I'm in no way
    connected to Jean Labrosse or Micrium ;-)

Regards,
Peter Tiang

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