[ECOS] basic question

Mandeep Sandhu mandeepsandhu.chd@gmail.com
Fri Jul 31 04:24:00 GMT 2009


On Thu, Jul 30, 2009 at 7:45 PM, Edgar Grimberg<edgar.grimberg@zylin.com> wrote:
> On Thu, Jul 30, 2009 at 1:46 PM, Mandeep
> Sandhu<mandeepsandhu.chd@gmail.com> wrote:
>> Hi All,
>>
>> A very basic question:
>>
>> What do people mean when they say running xyz app _without_ an operating
>> system?
>>
>> Does it mean that basic ecos kernel support is not there, i.e no
>> scheduler, HAL etc etc?
>>
>> What is an apps entry point then? Will it still call cyg_usre_start()
>> and the likes?
>
> The CPUs have defined a reset address (called reset vector and placed
> inside the exceptions vector), that is the entry point for the program
> counter when the power is ON, or when the CPU comes out of a hardware
> reset. The very first line of code is the embedded application "real"
> entry point. You will find eCos jumping from that place to _start. For
> example, for PowerPC:
>
> in packages/hal/powerpc/arch/current/src/vectors.S
>
> you can find thie code:
>
> # Reset vector macro
>        .macro  reset_vector name
>        .p2align 8
>        .globl  __exception_\name
> __exception_\name:
> #ifdef CYGSEM_HAL_POWERPC_RESET_USES_JUMP
>        bl      _start
> #else
>        lwi     r3,_start
>        mtlr    r3
>        blr
> #endif
>
> From that point on, eCos (or any other OS) will initialize the memory,
> peripherals and so on. By running without an OS, people often mean
> that you should write your own start-up routines and take care of
> (implement) the needed functions you will usually find in the OS. Of
> course, that means no cyg_user_start or anything like it.
> Unless you are really running out of memory (flash/ram to hold the
> application or ram to use it in the application) or out of CPU cycles
> (you want to optimize the "common" OS to death for you fancy
> application), I would not recommend investing the time to rewrite all
> that stuff.

Thanks for this detailed explanation Edgar. I too don't want to reinvent the
wheel unless it's absolutely necessary.

My app will mostly do network centric stuff, so that took me to the lwip mailing
list! :) Thats where I saw a lot people using lwip "w/o OS"....and hence my
question.

Regards,
-mandeep

>
> Regards,
> Edgar
>
>
>
>
>> Thanks,
>> -mandeep
>>
>> --
>> Before posting, please read the FAQ: http://ecos.sourceware.org/fom/ecos
>> and search the list archive: http://ecos.sourceware.org/ml/ecos-discuss
>>
>>
>

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