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 | | From: | funkymunky | | Subject: | why is a bootloader required? | | Date: | 30 Dec 2004 23:27:22 -0800 |
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 | Hi,
Im new to the arm family and embedded systems in general,till now iv
worked a bit on the 89c51.
Ive been puzzled by the following: why is a bootloader required in
controllers like the at91rm9200 im using right now? how come no
bootloader is required in a controller like the 89c51? Iv read a bit on
the need for a bootloader in a PC..but why would it be required on a
controller?
Also, the atmel manual mentions that a default bootloader is provided
in controllers like the one im using..my project involves porting of
Linux to this controller..why,then, is a seperate bootloader reqd??
thanx in anticipation
Mayank
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| | From: | Joe | | Subject: | Re: why is a bootloader required? | | Date: | Fri, 31 Dec 2004 11:16:45 +0000 |
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| funkymunky wrote:
> Hi,
>
> Im new to the arm family and embedded systems in general,till now iv
> worked a bit on the 89c51.
> Ive been puzzled by the following: why is a bootloader required in
> controllers like the at91rm9200 im using right now? how come no
> bootloader is required in a controller like the 89c51? Iv read a bit on
> the need for a bootloader in a PC..but why would it be required on a
> controller?
> Also, the atmel manual mentions that a default bootloader is provided
> in controllers like the one im using..my project involves porting of
> Linux to this controller..why,then, is a seperate bootloader reqd??
> thanx in anticipation
> Mayank
>
Linux is a portable OS, while boot up sequences are architecture
specific. Therefore boot loader is separated from the Linux Kernel.
In 8051 world, the OS are usually not portable, therefore boot up
code and OS can combine.
Also, in most cases the linux kernel image is compressed. Therefore
you need a small program to decompress it and put it in the RAM
(you don't want to execute it from ROM becasue ROM is ususally slower),
and then start executing the kernel.
Bootloader can also perform a number of hardware initializations,
self tests, verify the boot/OS image, or even allow you to select
one of the OS if there are multiple OS kernel images available.
Separating boot loader and Kernel can also make it easier for
firmware upgrade.
In 8051 uP, the memory is so small that having a boot loader may
reduce the maximum program size you can have.
Joe
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| | From: | paul.gotch at at-arm-dot.com | | Subject: | Re: why is a bootloader required? | | Date: | 31 Dec 2004 11:48:44 GMT |
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| Joe wrote:
> Also, in most cases the linux kernel image is compressed. Therefore
> you need a small program to decompress it and put it in the RAM
> (you don't want to execute it from ROM becasue ROM is ususally slower),
> and then start executing the kernel.
....however on many embedded devices you don't want to stuff that much RAM
in there. The other alternative is Execute In Place (EIP) with places the
readonly sections of the kernel in ROM and the readwrite sections in RAM. I
believe that this is being worked on for Linux.
This gives you faster startup times because you don't have to copy
everything out of ROM into RAM before you do anything. If you have got
enough RAM to have the kernel resident then you can demand copy the kernel
into RAM as you are running.
> Bootloader can also perform a number of hardware initialisations,
In some cases the bootloader has to do processor setup such as enabling
MMUs, enabling processor features which are disabled by default out of
reset and so on.
-p
--
Paul Gotch
CoreSight Tools
Development Systems ARM Limited.
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