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List:       uclinux-dev
Subject:    Re: [uClinux-dev] Bootloaders:  u-boot vs. micromonitor
From:       Greg Ungerer <gerg () snapgear ! com>
Date:       2008-06-25 5:00:31
Message-ID: 4861D0EF.7020702 () snapgear ! com
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rwarner wrote:
>>> missed something in the requirements of uCLinux start up.
>>> 1. Initialize and provide access to RAM/ROM and peripherals
>>>     A. change PLL
>>>     B. change chip select registers for RAM/ROM
>>>     C. setup AIC
>>>     D. setup WDT as necessary
>>>     E. ensure other peripherals are in a quiescent state
>>> 2. jump to 'stext'
>>
>> That's good for a first stage bootloader.  You might use it in a
>> rolled out system where you only update to tested firmware, or when
>> you have pins on the board to easily reflash it.
>>
>> Often it's useful to have a second stage with options to trap on a
>> diagnostic serial port, present a prompt, boot an alternative kernel,
>> read a file from the network and write it to flash, etc.  Sometimes
>> the second stage can be a small Linux kernel :-)
>>
> Jamie,
> 
> Yes, a more advanced bootloader like U-Boot and others provide these 
> enhancements.  You are correct in that remote or local reflash of target 
>  code can be a requirement.  As well as multi-backup boot images in case 
> a new download failed.  I forgot to add i did add a simple memtest to 
> SRAM.  Can quickly grow into it's own monster with unique requirements.  :)
> 
> thnx for the enhanced requirement list.

Or you can go without a boot loader altogether and boot directly
into uClinux. The setup code that you otherwise put in your boot
loader (DRAM setup for example) can be done in the uClinux start up
code. One example I know of in the uClinux-dist is for the M5249EVB.
(See its startup code at 
linux-2.4.x/arch/m68knommu/platform/5249/MOTOROLA/crt0_rom.S)

Doesn't necessarily make sense for every setup, but if you don't
have a lot of RAM it is an option.

Regards
Greg



------------------------------------------------------------------------
Greg Ungerer  --  Chief Software Dude       EMAIL:     gerg@snapgear.com
Secure Computing Corporation                PHONE:       +61 7 3435 2888
825 Stanley St,                             FAX:         +61 7 3891 3630
Woolloongabba, QLD, 4102, Australia         WEB: http://www.SnapGear.com
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