Embedded Linux?

Embedded Linux?

[Daniel Rodrick]

Hi list,

I'm a newbie, true to its every sense, and hence this question.

I have come across the term "Embedded Linux" a lot of times. Is
embedded linux a different branch of kernel all together? Or is it
that the vanila stock kernel (downloaded from kernel.org) becomes
"Embedded Linux" when compiled for an embedded processor like ARM /
PPC etc?

Thanks,

Dan

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Embedded Linux?

[Daniel Rodrick]

Hi list,

I'm a newbie, true to its every sense, and hence this question.

I have come across the term "Embedded Linux" a lot of times. Is
embedded linux a different branch of kernel all together? Or is it
that the vanila stock kernel (downloaded from kernel.org) becomes
"Embedded Linux" when compiled for an embedded processor like ARM /
PPC etc?


Thanks,

Dan
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Re: Embedded Linux?

[Ray Olszewski]

Daniel Rodrick wrote:
> Hi list,
> 
> I'm a newbie, true to its every sense, and hence this question.
> 
> I have come across the term "Embedded Linux" a lot of times. Is
> embedded linux a different branch of kernel all together? Or is it
> that the vanila stock kernel (downloaded from kernel.org) becomes
> "Embedded Linux" when compiled for an embedded processor like ARM /
> PPC etc?
> 
> 
> Thanks,

Not quite either of these things. Embedded Linux is an imprecise term, 
but it generally refers to specialized distributions that are adapted to 
embedded processors and to other limitations of embedded systems (such 
as use of flash memory instead of a hard disk).

And it covers more than the kernel. A typical Embedded Linux system 
includes the kernel, a suitable cross-compiler (a version of gcc that 
runs on i86 hardware, say, but produces output for an ARM5), a few 
associated things (an assembler, glibc) that are collectively called the 
"toolchain", and some stripped-down apps (like busybox). The kernel may 
have non-standard patches needed to get it to work with the target 
hardware ... but there is a strong push to get those patches integrated 
into the main kernel, and it usually works pretty well (at least for 
ARM, the one embedded processor I spend some time working with).

Commercial Embedded Linux distributions (from Lynuxworks, Monte Vista, 
and maybe others ... I'm way out of date here) typically include non-OS 
tools that the vendors claim facilitate cross development.

All this is really an oversimplification, though ... but probably enough 
to get you started.

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Re: Embedded Linux?

[Daniel Rodrick]

> Not quite either of these things. Embedded Linux is an imprecise term,
> but it generally refers to specialized distributions that are adapted to
> embedded processors and to other limitations of embedded systems (such
> as use of flash memory instead of a hard disk).
>
> And it covers more than the kernel. A typical Embedded Linux system
> includes the kernel, a suitable cross-compiler (a version of gcc that
> runs on i86 hardware, say, but produces output for an ARM5), a few
> associated things (an assembler, glibc) that are collectively called the
> "toolchain", and some stripped-down apps (like busybox). The kernel may
> have non-standard patches needed to get it to work with the target
> hardware ... but there is a strong push to get those patches integrated
> into the main kernel, and it usually works pretty well (at least for
> ARM, the one embedded processor I spend some time working with).
>

Thanks. So what I get is that there is no term such as "Embedded Linux
Kernel". There are embedded distributions however, that contain kernel
(compiled for an embedded architecture) with specific patches (by the
ditribution vendor) for the specific embedded platform (ARM / PPC
etc).

But CAN I run standard stock kernel compilerd for an embedded chip
(say ARM) on an ARM processor? Or do I NECESSARILY need the patches by
the distribution?

Thanks,

Dan
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Re: Embedded Linux?

[Bernd Petrovitsch]

On Thu, 2006-06-22 at 12:07 +0530, Daniel Rodrick wrote:
[...]
> I'm a newbie, true to its every sense, and hence this question.
> 
> I have come across the term "Embedded Linux" a lot of times. Is
> embedded linux a different branch of kernel all together? Or is it

Not really.

> that the vanila stock kernel (downloaded from kernel.org) becomes
> "Embedded Linux" when compiled for an embedded processor like ARM /
> PPC etc?

Yes. But nowadays there also "embedded" boards with Intel-compatible
CPUs (e.g. Celerons, VIA-C[23], etc. on PC104 boards, SoC, etc).
And not all PPCs can be considered "embedded" - think of IBM high-end
PPC machines.

	Bernd
-- 
Firmix Software GmbH                   http://www.firmix.at/
mobil: +43 664 4416156                 fax: +43 1 7890849-55
          Embedded Linux Development and Services


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Re: Embedded Linux?

[Arjan van de Ven]

On Thu, 2006-06-22 at 12:07 +0530, Daniel Rodrick wrote:
> Hi list,
> 
> I'm a newbie, true to its every sense, and hence this question.
> 
> I have come across the term "Embedded Linux" a lot of times. Is
> embedded linux a different branch of kernel all together? Or is it
> that the vanila stock kernel (downloaded from kernel.org) becomes
> "Embedded Linux" when compiled for an embedded processor like ARM /
> PPC etc?

it's usually the same kernel (but with a stripped down .config); the
main difference tends to be in the userspace that is used... busybox and
ulibc and other 'smaller than normal linux' components tend to be used..


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Re: Embedded Linux?

[Jesper Juhl]

On 22/06/06, Daniel Rodrick <daniel.rodrick@gmail.com> wrote:
> Hi list,
>
> I'm a newbie, true to its every sense, and hence this question.
>
> I have come across the term "Embedded Linux" a lot of times. Is
> embedded linux a different branch of kernel all together? Or is it

Some embedded uses of Linux use the vanilla kernel, some use highly
modified kernels custom, some use vendor kernels. What makes a Linux
kernel embedded is simply that it is used as such.

> that the vanila stock kernel (downloaded from kernel.org) becomes
> "Embedded Linux" when compiled for an embedded processor like ARM /
> PPC etc?

Embedded boards can be found with almost any CPU available under the
sun. You can get embedded boards with arm/ppc/pentium/opteron/c3/sparc
and many more. The type of CPU does not determine if something is
embedded or not. Also, many CPU's that are often used for embedded
projects are also used elsewhere.

Simply put; if you use Linux (in whatever form with whatever hardware)
in an embedded application/project, then it becomes "Embedded Linux" -
simple as that.


-- 
Jesper Juhl <jesper.juhl@gmail.com>
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Re: Embedded Linux?

[Jesper Juhl]

On 22/06/06, Daniel Rodrick <daniel.rodrick@gmail.com> wrote:
> Hi list,
>
> I'm a newbie, true to its every sense, and hence this question.
>
> I have come across the term "Embedded Linux" a lot of times. Is
> embedded linux a different branch of kernel all together? Or is it

Some embedded uses of Linux use the vanilla kernel, some use highly
modified kernels custom, some use vendor kernels. What makes a Linux
kernel embedded is simply that it is used as such.

> that the vanila stock kernel (downloaded from kernel.org) becomes
> "Embedded Linux" when compiled for an embedded processor like ARM /
> PPC etc?

Embedded boards can be found with almost any CPU available under the
sun. You can get embedded boards with arm/ppc/pentium/opteron/c3/sparc
and many more. The type of CPU does not determine if something is
embedded or not. Also, many CPU's that are often used for embedded
projects are also used elsewhere.

Simply put; if you use Linux (in whatever form with whatever hardware)
in an embedded application/project, then it becomes "Embedded Linux" -
simple as that.


--
Jesper Juhl <jesper.juhl@gmail.com>
Don't top-post  http://www.catb.org/~esr/jargon/html/T/top-post.html
Plain text mails only, please      http://www.expita.com/nomime.html
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Re: Embedded Linux?

[Ray Olszewski]

Daniel Rodrick wrote:
>> Not quite either of these things. Embedded Linux is an imprecise term,
>> but it generally refers to specialized distributions that are adapted to
>> embedded processors and to other limitations of embedded systems (such
>> as use of flash memory instead of a hard disk).
>>
>> And it covers more than the kernel. A typical Embedded Linux system
>> includes the kernel, a suitable cross-compiler (a version of gcc that
>> runs on i86 hardware, say, but produces output for an ARM5), a few
>> associated things (an assembler, glibc) that are collectively called the
>> "toolchain", and some stripped-down apps (like busybox). The kernel may
>> have non-standard patches needed to get it to work with the target
>> hardware ... but there is a strong push to get those patches integrated
>> into the main kernel, and it usually works pretty well (at least for
>> ARM, the one embedded processor I spend some time working with).
>>
> 
> Thanks. So what I get is that there is no term such as "Embedded Linux
> Kernel". There are embedded distributions however, that contain kernel
> (compiled for an embedded architecture) with specific patches (by the
> ditribution vendor) for the specific embedded platform (ARM / PPC
> etc).
> 
> But CAN I run standard stock kernel compilerd for an embedded chip
> (say ARM) on an ARM processor? Or do I NECESSARILY need the patches by
> the distribution?

Id depends. To state the obvious, one doesn't run Linux on a CPU; one 
runs it on a computer, which has more in it than a CPU. Some kernel 
patches involve, for example, the video framebuffer, or support for 
flash memory and associated filesystems (e.g., jffs2), or ... you get 
the idea. (It's been a couple of years since I did any ARM work, and my 
memory of the details is getting a bit rusty.)

Often, embedded CPUs are part of SoCs (Systems on Chip) that integrate 
some of the support stuff into a single chip with the CPU, and that can 
impose additional requirements on the kernel or core apps.

In practice, when I worked with ARM systems, we always expected the 
board vendor to provide the core ... a working kernel, at least a 
command-line video interface, the basic app set needed for the system to 
work (mostly busybox, plus a few other things), support for jffs2, and a 
native- or cross-compile toolchain. It is possible to do this yourself 
for a new board (obviously, since the vendors do it), but when we looked 
at that option, it looked like a lot of work.

For ARM, at least, all this stuff was well developed. There was a 
standard set of kernel patches that provided most, maybe all (I forget), 
of the ARM-specific functionality.

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