[U-Boot] Need answers of basic questions regarding u-boot

[Hebbar, Gururaja]

Hi,

We need to make this sticky or add it into some wiki page.

Nice explanation for beginners.

Regards
Gururaja

On Mon, Aug 08, 2011 at 01:58:32, Jerry Van Baren wrote:
> On 08/07/2011 02:55 PM, Rakesh Modi wrote:
> > Hi,
> > I am new to linux and u-boot. Please answer my following questions.
> > 1) what is u-boot? why it require?
> 
> It initializes and configures the hardware (processor, RAM, peripherals), it loads linux (or other OS) from storage (flash, hard drive, ethernet, other) into RAM and then passes control to linux.
> 
> While it isn't required, it is very convenient to have it.  The other features of u-boot are that u-boot can be used to load new linux images into your storage device.  The general principle is that u-boot is not often replaced on a board, but the linux image is updated and upgraded regularly.
> 
> > 2) why we can not load linux kernel directly without use of u-boot?
> 
> You can, but you need to do the hardware initialization and configuration in the linux start up code.  You will also have to create a method to and mechanism for linux to upgrade itself, preferably in a "failure resistant" way so that you don't "brick" your board inadvertently by having a failure when upgrading linux.
> 
> U-boot has solved these problems already for you.
> 
> > 3) How does any processor sequence starts when power is on?
> 
> That is described in the processor hardware reference manual.  It is different for each processor, but in general the processor starts fetching and executing code from a known location - sometimes from a fixed memory address, sometimes it fetches a pointer from a fixed memory address and starts executing from the address pointed to.
> 
> Best regards,
> gvb
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Regards, 
Gururaja