Re: Self booting systems with out bootloader?!!!

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Date: Tue, 25 Jan 2005 01:27:02 GMT

"s.subbarayan" wrote:

> Dear all,
>

> 1)I am not getting the relation between fragmentation and storing the
> data in low address area of RAM.How does loading data section in low
> address area prevent fragmentation?
>

if you load it in the middle of memory, you immediately start with two
'fragments' of memory devoted to the memory pool, so you can't allocate
all of memory in one chunk. So you gotta load at the top or bottom.

>
> 2)My query is what do you mean generally when you say "self booting"
> systems?
>

they are just talking about not having a bootloader, I think. Had to have
some way of informing their customers that now vxworks could do what most
other embedded systems have always done, and this is the sales
terminology.

>
> 3)Does that mean there is no RAM present and the code executes fully
> from ROM?

>

nope. They won't have been able to create a kernel that can run without
variables stored in RAM. But from the quotes you gave it does indicate
that you can run the kernel from ROM so you won't need enough RAM to load
the whole kernel into.

>
> 4)If thats the case,then the second sentence as stated above confuses
> me,because it says the data section will be present in
> RAM_LOW_ADDRESS.Can some one clarify me this?
>

you need variables in RAM for any real product... and the kernel will
reserve space for its own variables as well.

>
> AFAIK,when we say selfbooting,this applies for production systems in
> some embedded products(not for every embedded device) where the code
> will be executing completely from ROM and boot code will not get
> copied to RAM and code will be executed from ROM.Is this understanding
> correct?

Based on the quotes you gave, I think that is a fair assessment of the
situation.

>
>
> I have worked with avionics protocols and consumer electronics related
> embedded systems.But I am curious enough to know what sort of embedded
> applications can be created with ROM only version with out
> bootloader?IMHO its going to be taking more time to boot from ROM as
> compared to RAM.Given the fact that,most embedded systems are for
> mission critical stuff,what will be advantage in moving to ROM only
> systems?I think consumer electronics apps are less critical as
> compared to medical and avionics systems,but still in the consumer
> electronics devices (typically DVD player,STB),I have worked with had
> a boot loader and was not executing from ROM.
>

Well for example we do life-safety systems that aren't usually high-speed,
and for a lot of it we don't use VxWorks but code close to the metal, e.g.
by putting our own start addresses in the processor's initialization
vector and bringing the board up ourself. We run these systems entirely
out of ROM chips (actually FLASH chips) rather than placing other types
of storage into the system. It has been said there are far more embedded
computers than there are desktop computers... and in the early days *ALL*
of them were done this way, even today I don't think it is uncommon
although more and more we start with a basic operating system except when
production quantity means cost scaling can't do with run-time licenses.

But also more and more even in these systems, a separate 'boot' app is
added that has basic functionality such as the ability to download a new
image into the flash chips or maybe self test code.

David

• Previous message: Nicholas O. Lindan: "Re: bluetooth->RS232"
• In reply to: s.subbarayan: "Self booting systems with out bootloader?!!!"
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